/*      $NetBSD: uatp.c,v 1.31 2022/03/28 12:45:04 riastradh Exp $      */

/*-
 * Copyright (c) 2011-2014 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Taylor R. Campbell.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * uatp(4) - USB Apple Trackpad
 *
 * The uatp driver talks the protocol of the USB trackpads found in
 * Apple laptops since 2005, including PowerBooks, iBooks, MacBooks,
 * and MacBook Pros.  Some of these also present generic USB HID mice
 * on another USB report id, which the ums(4) driver can handle, but
 * Apple's protocol gives more detailed sensor data that lets us detect
 * multiple fingers to emulate multi-button mice and scroll wheels.
 */

/*
 * Protocol
 *
 * The device has a set of horizontal sensors, each being a column at a
 * particular position on the x axis that tells you whether there is
 * pressure anywhere on that column, and vertical sensors, each being a
 * row at a particular position on the y axis that tells you whether
 * there is pressure anywhere on that row.
 *
 * Whenever the device senses anything, it emits a readout of all of
 * the sensors, in some model-dependent order.  (For the order, see
 * read_sample_1 and read_sample_2.)  Each sensor datum is an unsigned
 * eight-bit quantity representing some measure of pressure.  (Of
 * course, it really measures capacitance, not pressure, but we'll call
 * it `pressure' here.)
 */

/*
 * Interpretation
 *
 * To interpret the finger's position on the trackpad, the driver
 * computes a weighted average over all possible positions, weighted by
 * the pressure at that position.  The weighted average is computed in
 * the dimensions of the screen, rather than the trackpad, in order to
 * admit a finer resolution of positions than the trackpad grid.
 *
 * To update the finger's position smoothly on the trackpad, the driver
 * computes a weighted average of the old raw position, the old
 * smoothed position, and the new smoothed position.  The weights are
 * given by the old_raw_weight, old_smoothed_weight, and new_raw_weight
 * sysctl knobs.
 *
 * Finally, to move the cursor, the driver takes the difference between
 * the old and new positions and accelerates it according to some
 * heuristic knobs that need to be reworked.
 *
 * Finally, there are some bells & whistles to detect tapping and to
 * emulate a three-button mouse by leaving two or three fingers on the
 * trackpad while pressing the button.
 */

/*
 * Future work
 *
 * With the raw sensor data available, we could implement fancier bells
 * & whistles too, such as pinch-to-zoom.  However, wsmouse supports
 * only four-dimensional mice with buttons, and we already use two
 * dimensions for mousing and two dimensions for scrolling, so there's
 * no straightforward way to report zooming and other gestures to the
 * operating system.  Probably a better way to do this would be just to
 * attach uhid(4) instead of uatp(4) and to read the raw sensors data
 * yourself -- but that requires hairy mode switching for recent models
 * (see geyser34_enable_raw_mode).
 *
 * XXX Rework the acceleration knobs.
 * XXX Implement edge scrolling.
 * XXX Fix sysctl setup; preserve knobs across suspend/resume.
 *     (uatp0 detaches and reattaches across suspend/resume, so as
 *     written, the sysctl tree is torn down and rebuilt, losing any
 *     state the user may have set.)
 * XXX Refactor motion state so I can understand it again.
 *     Should make a struct uatp_motion for all that state.
 * XXX Add hooks for ignoring trackpad input while typing.
 */

/*
 * Classifying devices
 *
 * I have only one MacBook to test this driver, but the driver should
 * be applicable to almost every Apple laptop made since the beginning
 * of 2005, so the driver reports lots of debugging output to help to
 * classify devices.  Boot with `boot -v' (verbose) and check the
 * output of `dmesg | grep uatp' to answer the following questions:
 *
 * - What devices (vendor, product, class, subclass, proto, USB HID
 *   report dump) fail to attach when you think they should work?
 *     (vendor not apple, class not hid, proto not mouse)
 *
 * - What devices have an unknown product id?
 *     `unknown vendor/product id'
 *
 * - What devices have the wrong screen-to-trackpad ratios?
 *     `... x sensors, scaled by ... for ... points on screen'
 *     `... y sensors, scaled by ... for ... points on screen'
 *   You can tweak hw.uatp0.x_ratio and hw.uatp0.y_ratio to adjust
 *   this, up to a maximum of 384 for each value.
 *
 * - What devices have the wrong input size?
 *     `expected input size ... but got ... for Apple trackpad'
 *
 * - What devices give wrong-sized packets?
 *     `discarding ...-byte input'
 *
 * - What devices split packets in chunks?
 *     `partial packet: ... bytes'
 *
 * - What devices develop large sensor readouts?
 *     `large sensor readout: ...'
 *
 * - What devices have the wrong number of sensors?  Are there parts of
 *   your trackpad that the system doesn't seem to notice?  You can
 *   tweak hw.uatp0.x_sensors and hw.uatp0.y_sensors, up to a maximum
 *   of 32 for each value.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: uatp.c,v 1.31 2022/03/28 12:45:04 riastradh Exp $");

#ifdef _KERNEL_OPT
#include "opt_usb.h"
#endif

#include <sys/types.h>
#include <sys/param.h>
#include <sys/atomic.h>
#include <sys/device.h>
#include <sys/errno.h>
#include <sys/ioctl.h>
#include <sys/kernel.h>
#include <sys/module.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/time.h>

/* Order is important here...sigh...  */
#include <dev/usb/usb.h>
#include <dev/usb/usbdi.h>
#include <dev/usb/usbdi_util.h>
#include <dev/usb/usbdevs.h>
#include <dev/usb/uhidev.h>
#include <dev/usb/usbhid.h>
#include <dev/hid/hid.h>

#include <dev/wscons/wsconsio.h>
#include <dev/wscons/wsmousevar.h>

#define CHECK(condition, fail) do {                                     \
        if (! (condition)) {                                            \
                aprint_error_dev(uatp_dev(sc), "%s: check failed: %s\n",\
                        __func__, #condition);                          \
                fail;                                                   \
        }                                                               \
} while (0)

#define UATP_DEBUG_ATTACH       __BIT(0)
#define UATP_DEBUG_MISC         __BIT(1)
#define UATP_DEBUG_WSMOUSE      __BIT(2)
#define UATP_DEBUG_IOCTL        __BIT(3)
#define UATP_DEBUG_RESET        __BIT(4)
#define UATP_DEBUG_INTR         __BIT(5)
#define UATP_DEBUG_PARSE        __BIT(6)
#define UATP_DEBUG_TAP          __BIT(7)
#define UATP_DEBUG_EMUL_BUTTON  __BIT(8)
#define UATP_DEBUG_ACCUMULATE   __BIT(9)
#define UATP_DEBUG_STATUS       __BIT(10)
#define UATP_DEBUG_SPURINTR     __BIT(11)
#define UATP_DEBUG_MOVE         __BIT(12)
#define UATP_DEBUG_ACCEL        __BIT(13)
#define UATP_DEBUG_TRACK_DIST   __BIT(14)
#define UATP_DEBUG_PALM         __BIT(15)

/*
 * Unconditionally enable the debug output so you don't have to
 * recompile the kernel to diagnose it.  This is not a high-throughput
 * NIC driver or anything that will be hurt by a few conditionals.
 */
#define UATP_DEBUG      1

#if UATP_DEBUG
#  define DPRINTF(sc, flags, format) do {                               \
        if ((flags) & (sc)->sc_debug_flags) {                           \
                printf("%s: %s: ", device_xname(uatp_dev(sc)), __func__); \
                printf format;                                          \
        }                                                               \
} while (0)
#else
#  define DPRINTF(sc, flags, format) do {} while (0)
#endif

/* Maximum number of bytes in an incoming packet of sensor data.  */
#define UATP_MAX_INPUT_SIZE     81

/* Maximum number of sensors in each dimension.  */
#define UATP_MAX_X_SENSORS      32
#define UATP_MAX_Y_SENSORS      32
#define UATP_MAX_SENSORS        32
#define UATP_SENSORS            (UATP_MAX_X_SENSORS + UATP_MAX_Y_SENSORS)

/* Maximum accumulated sensor value.  */
#define UATP_MAX_ACC            0xff

/* Maximum screen dimension to sensor dimension ratios.  */
#define UATP_MAX_X_RATIO        0x180
#define UATP_MAX_Y_RATIO        0x180
#define UATP_MAX_RATIO          0x180

/* Maximum weight for positions in motion calculation.  */
#define UATP_MAX_WEIGHT         0x7f

/* Maximum possible trackpad position in a single dimension.  */
#define UATP_MAX_POSITION       (UATP_MAX_SENSORS * UATP_MAX_RATIO)

/* Bounds on acceleration.  */
#define UATP_MAX_MOTION_MULTIPLIER      16

/* Status bits transmitted in the last byte of an input packet.  */
#define UATP_STATUS_BUTTON      __BIT(0)        /* Button pressed */
#define UATP_STATUS_BASE        __BIT(2)        /* Base sensor data */
#define UATP_STATUS_POST_RESET  __BIT(4)        /* Post-reset */

/* Forward declarations */

struct uatp_softc;              /* Device driver state.  */
struct uatp_descriptor;         /* Descriptor for a particular model.  */
struct uatp_parameters;         /* Parameters common to a set of models.  */
struct uatp_knobs;              /* User-settable configuration knobs.  */
enum uatp_tap_state {
        TAP_STATE_INITIAL,
        TAP_STATE_TAPPING,
        TAP_STATE_TAPPED,
        TAP_STATE_DOUBLE_TAPPING,
        TAP_STATE_DRAGGING_DOWN,
        TAP_STATE_DRAGGING_UP,
        TAP_STATE_TAPPING_IN_DRAG,
};

static const struct uatp_descriptor *find_uatp_descriptor
    (const struct uhidev_attach_arg *);
static device_t uatp_dev(const struct uatp_softc *);
static uint8_t *uatp_x_sample(struct uatp_softc *);
static uint8_t *uatp_y_sample(struct uatp_softc *);
static int *uatp_x_acc(struct uatp_softc *);
static int *uatp_y_acc(struct uatp_softc *);
static void uatp_clear_position(struct uatp_softc *);
static unsigned int uatp_x_sensors(const struct uatp_softc *);
static unsigned int uatp_y_sensors(const struct uatp_softc *);
static unsigned int uatp_x_ratio(const struct uatp_softc *);
static unsigned int uatp_y_ratio(const struct uatp_softc *);
static unsigned int uatp_old_raw_weight(const struct uatp_softc *);
static unsigned int uatp_old_smoothed_weight(const struct uatp_softc *);
static unsigned int uatp_new_raw_weight(const struct uatp_softc *);
static int scale_motion(const struct uatp_softc *, int, int *,
    const unsigned int *, const unsigned int *);
static int uatp_scale_motion(const struct uatp_softc *, int, int *);
static int uatp_scale_fast_motion(const struct uatp_softc *, int, int *);
static int uatp_match(device_t, cfdata_t, void *);
static void uatp_attach(device_t, device_t, void *);
static void uatp_setup_sysctl(struct uatp_softc *);
static bool uatp_setup_sysctl_knob(struct uatp_softc *, int *, const char *,
    const char *);
static void uatp_childdet(device_t, device_t);
static int uatp_detach(device_t, int);
static int uatp_activate(device_t, enum devact);
static int uatp_enable(void *);
static void uatp_disable(void *);
static int uatp_ioctl(void *, unsigned long, void *, int, struct lwp *);
static void geyser34_enable_raw_mode(struct uatp_softc *);
static void geyser34_initialize(struct uatp_softc *);
static void geyser34_finalize(struct uatp_softc *);
static void geyser34_deferred_reset(struct uatp_softc *);
static void geyser34_reset_task(void *);
static void uatp_intr(void *, void *, unsigned int);
static bool base_sample_softc_flag(const struct uatp_softc *, const uint8_t *);
static bool base_sample_input_flag(const struct uatp_softc *, const uint8_t *);
static void read_sample_1(uint8_t *, uint8_t *, const uint8_t *);
static void read_sample_2(uint8_t *, uint8_t *, const uint8_t *);
static void accumulate_sample_1(struct uatp_softc *);
static void accumulate_sample_2(struct uatp_softc *);
static void uatp_input(struct uatp_softc *, uint32_t, int, int, int, int);
static uint32_t uatp_tapped_buttons(struct uatp_softc *);
static bool interpret_input(struct uatp_softc *, int *, int *, int *, int *,
    uint32_t *);
static unsigned int interpret_dimension(struct uatp_softc *, const int *,
    unsigned int, unsigned int, unsigned int *, unsigned int *);
static void tap_initialize(struct uatp_softc *);
static void tap_finalize(struct uatp_softc *);
static void tap_enable(struct uatp_softc *);
static void tap_disable(struct uatp_softc *);
static void tap_transition(struct uatp_softc *, enum uatp_tap_state,
    const struct timeval *, unsigned int, unsigned int);
static void tap_transition_initial(struct uatp_softc *);
static void tap_transition_tapping(struct uatp_softc *, const struct timeval *,
    unsigned int);
static void tap_transition_double_tapping(struct uatp_softc *,
    const struct timeval *, unsigned int);
static void tap_transition_dragging_down(struct uatp_softc *);
static void tap_transition_tapping_in_drag(struct uatp_softc *,
    const struct timeval *, unsigned int);
static void tap_transition_tapped(struct uatp_softc *, const struct timeval *);
static void tap_transition_dragging_up(struct uatp_softc *);
static void tap_reset(struct uatp_softc *);
static void tap_reset_wait(struct uatp_softc *);
static void tap_touched(struct uatp_softc *, unsigned int);
static bool tap_released(struct uatp_softc *);
static void schedule_untap(struct uatp_softc *);
static void untap_callout(void *);
static uint32_t emulated_buttons(struct uatp_softc *, unsigned int);
static void update_position(struct uatp_softc *, unsigned int,
    unsigned int, unsigned int, int *, int *, int *, int *);
static void move_mouse(struct uatp_softc *, unsigned int, unsigned int,
    int *, int *);
static void scroll_wheel(struct uatp_softc *, unsigned int, unsigned int,
    int *, int *);
static void move(struct uatp_softc *, const char *, unsigned int, unsigned int,
    int *, int *, int *, int *, unsigned int *, unsigned int *, int *, int *);
static int smooth(struct uatp_softc *, unsigned int, unsigned int,
    unsigned int);
static bool motion_below_threshold(struct uatp_softc *, unsigned int,
    int, int);
static int accelerate(struct uatp_softc *, unsigned int, unsigned int,
    unsigned int, unsigned int, bool, int *);

struct uatp_knobs {
        /*
         * Button emulation.  What do we do when two or three fingers
         * are on the trackpad when the user presses the button?
         */
        unsigned int two_finger_buttons;
        unsigned int three_finger_buttons;

#if 0
        /*
         * Edge scrolling.
         *
         * XXX Implement this.  What units should these be in?
         */
        unsigned int top_edge;
        unsigned int bottom_edge;
        unsigned int left_edge;
        unsigned int right_edge;
#endif

        /*
         * Multifinger tracking.  What do we do with multiple fingers?
         * 0. Ignore them.
         * 1. Try to interpret them as ordinary mousing.
         * 2. Act like a two-dimensional scroll wheel.
         */
        unsigned int multifinger_track;

        /*
         * Sensor parameters.
         */
        unsigned int x_sensors;
        unsigned int x_ratio;
        unsigned int y_sensors;
        unsigned int y_ratio;
        unsigned int sensor_threshold;
        unsigned int sensor_normalizer;
        unsigned int palm_width;
        unsigned int old_raw_weight;
        unsigned int old_smoothed_weight;
        unsigned int new_raw_weight;

        /*
         * Motion parameters.
         *
         * XXX There should be a more principled model of acceleration.
         */
        unsigned int motion_remainder;
        unsigned int motion_threshold;
        unsigned int motion_multiplier;
        unsigned int motion_divisor;
        unsigned int fast_motion_threshold;
        unsigned int fast_motion_multiplier;
        unsigned int fast_motion_divisor;
        unsigned int fast_per_direction;
        unsigned int motion_delay;

        /*
         * Tapping.
         */
        unsigned int tap_limit_msec;
        unsigned int double_tap_limit_msec;
        unsigned int one_finger_tap_buttons;
        unsigned int two_finger_tap_buttons;
        unsigned int three_finger_tap_buttons;
        unsigned int tap_track_distance_limit;
};

static const struct uatp_knobs default_knobs = {
        /*
         * Button emulation.  Fingers on the trackpad don't change it
         * by default -- it's still the left button.
         *
         * XXX The left button should have a name.
         */
         .two_finger_buttons    = 1,
         .three_finger_buttons  = 1,

#if 0
        /*
         * Edge scrolling.  Off by default.
         */
        .top_edge               = 0,
        .bottom_edge            = 0,
        .left_edge              = 0,
        .right_edge             = 0,
#endif

        /*
         * Multifinger tracking.  Ignore by default.
         */
         .multifinger_track     = 0,

        /*
         * Sensor parameters.
         */
        .x_sensors              = 0,    /* default for model */
        .x_ratio                = 0,    /* default for model */
        .y_sensors              = 0,    /* default for model */
        .y_ratio                = 0,    /* default for model */
        .sensor_threshold       = 5,
        .sensor_normalizer      = 5,
        .palm_width             = 0,    /* palm detection disabled */
        .old_raw_weight         = 0,
        .old_smoothed_weight    = 5,
        .new_raw_weight         = 1,

        /*
         * Motion parameters.
         */
        .motion_remainder       = 1,
        .motion_threshold       = 0,
        .motion_multiplier      = 1,
        .motion_divisor         = 1,
        .fast_motion_threshold  = 10,
        .fast_motion_multiplier = 3,
        .fast_motion_divisor    = 2,
        .fast_per_direction     = 0,
        .motion_delay           = 4,

        /*
         * Tapping.  Disabled by default, with a reasonable time set
         * nevertheless so that you can just set the buttons to enable
         * it.
         */
        .tap_limit_msec                 = 100,
        .double_tap_limit_msec          = 200,
        .one_finger_tap_buttons         = 0,
        .two_finger_tap_buttons         = 0,
        .three_finger_tap_buttons       = 0,
        .tap_track_distance_limit       = 200,
};

struct uatp_softc {
        device_t sc_dev;
        struct uhidev *sc_hdev;         /* uhidev(9) parent.  */
        struct usbd_device *sc_udev;    /* USB device.  */
        struct usbd_interface *sc_iface0; /* Geyser 3/4 reset interface.  */
        device_t sc_wsmousedev;         /* Attached wsmouse device.  */
        const struct uatp_parameters *sc_parameters;
        struct uatp_knobs sc_knobs;
        struct sysctllog *sc_log;       /* Log for sysctl knobs.  */
        const struct sysctlnode *sc_node;       /* Our sysctl node.  */
        unsigned int sc_input_size;     /* Input packet size.  */
        uint8_t sc_input[UATP_MAX_INPUT_SIZE];  /* Buffer for a packet.   */
        unsigned int sc_input_index;    /* Current index into sc_input.  */
        int sc_acc[UATP_SENSORS];       /* Accumulated sensor state.  */
        uint8_t sc_base[UATP_SENSORS];  /* Base sample.  */
        uint8_t sc_sample[UATP_SENSORS];/* Current sample.  */
        unsigned int sc_motion_timer;   /* XXX describe; motion_delay  */
        int sc_x_raw;                   /* Raw horiz. mouse position.  */
        int sc_y_raw;                   /* Raw vert. mouse position.  */
        int sc_z_raw;                   /* Raw horiz. scroll position.  */
        int sc_w_raw;                   /* Raw vert. scroll position.  */
        int sc_x_smoothed;              /* Smoothed horiz. mouse position.  */
        int sc_y_smoothed;              /* Smoothed vert. mouse position.  */
        int sc_z_smoothed;              /* Smoothed horiz. scroll position.  */
        int sc_w_smoothed;              /* Smoothed vert. scroll position.  */
        int sc_x_remainder;             /* Remainders from acceleration.  */
        int sc_y_remainder;
        int sc_z_remainder;
        int sc_w_remainder;
        unsigned int sc_track_distance; /* Distance^2 finger has tracked,
                                         * squared to avoid sqrt in kernel.  */
        uint32_t sc_status;             /* Status flags:  */
#define UATP_ENABLED    __BIT(0)        /* . Is the wsmouse enabled?  */
#define UATP_DYING      __BIT(1)        /* . Have we been deactivated?  */
#define UATP_VALID      __BIT(2)        /* . Do we have valid sensor data?  */
        struct usb_task sc_reset_task;  /* Task for resetting device.  */

        callout_t sc_untap_callout;     /* Releases button after tap.  */
        kmutex_t sc_tap_mutex;          /* Protects the following fields.  */
        enum uatp_tap_state sc_tap_state;       /* Current tap state.  */
        unsigned int sc_tapping_fingers;        /* No. fingers tapping.  */
        unsigned int sc_tapped_fingers; /* No. fingers of last tap.  */
        struct timeval sc_tap_timer;    /* Timer for tap state transitions.  */
        uint32_t sc_buttons;            /* Physical buttons pressed.  */
        uint32_t sc_all_buttons;        /* Buttons pressed or tapped.  */

#if UATP_DEBUG
        uint32_t sc_debug_flags;        /* Debugging output enabled.  */
#endif
};

struct uatp_descriptor {
        uint16_t vendor;
        uint16_t product;
        const char *description;
        const struct uatp_parameters *parameters;
};

struct uatp_parameters {
        unsigned int x_ratio;           /* Screen width / trackpad width.  */
        unsigned int x_sensors;         /* Number of horizontal sensors.  */
        unsigned int x_sensors_17;      /* XXX Same, on a 17" laptop.  */
        unsigned int y_ratio;           /* Screen height / trackpad height.  */
        unsigned int y_sensors;         /* Number of vertical sensors.  */
        unsigned int input_size;        /* Size in bytes of input packets.  */

        /* Device-specific initialization routine.  May be null.  */
        void (*initialize)(struct uatp_softc *);

        /* Device-specific finalization routine.  May be null.  */
        void (*finalize)(struct uatp_softc *);

        /* Tests whether this is a base sample.  Second argument is
         * input_size bytes long.  */
        bool (*base_sample)(const struct uatp_softc *, const uint8_t *);

        /* Reads a sensor sample from an input packet.  First argument
         * is UATP_MAX_X_SENSORS bytes long; second, UATP_MAX_Y_SENSORS
         * bytes; third, input_size bytes.  */
        void (*read_sample)(uint8_t *, uint8_t *, const uint8_t *);

        /* Accumulates sensor state in sc->sc_acc.  */
        void (*accumulate)(struct uatp_softc *);

        /* Called on spurious interrupts to reset.  May be null.  */
        void (*reset)(struct uatp_softc *);
};

/* Known device parameters */

static const struct uatp_parameters fountain_parameters = {
        .x_ratio        = 64,   .x_sensors = 16,        .x_sensors_17 = 26,
        .y_ratio        = 43,   .y_sensors = 16,
        .input_size     = 81,
        .initialize     = NULL,
        .finalize       = NULL,
        .base_sample    = base_sample_softc_flag,
        .read_sample    = read_sample_1,
        .accumulate     = accumulate_sample_1,
        .reset          = NULL,
};

static const struct uatp_parameters geyser_1_parameters = {
        .x_ratio        = 64,   .x_sensors = 16,        .x_sensors_17 = 26,
        .y_ratio        = 43,   .y_sensors = 16,
        .input_size     = 81,
        .initialize     = NULL,
        .finalize       = NULL,
        .base_sample    = base_sample_softc_flag,
        .read_sample    = read_sample_1,
        .accumulate     = accumulate_sample_1,
        .reset          = NULL,
};

static const struct uatp_parameters geyser_2_parameters = {
        .x_ratio        = 64,   .x_sensors = 15,        .x_sensors_17 = 20,
        .y_ratio        = 43,   .y_sensors = 9,
        .input_size     = 64,
        .initialize     = NULL,
        .finalize       = NULL,
        .base_sample    = base_sample_softc_flag,
        .read_sample    = read_sample_2,
        .accumulate     = accumulate_sample_1,
        .reset          = NULL,
};

/*
 * The Geyser 3 and Geyser 4 share parameters.  They also present
 * generic USB HID mice on a different report id, so we have smaller
 * packets by one byte (uhidev handles multiplexing report ids) and
 * extra initialization work to switch the mode from generic USB HID
 * mouse to Apple trackpad.
 */

static const struct uatp_parameters geyser_3_4_parameters = {
        .x_ratio        = 64,   .x_sensors = 20, /* XXX */ .x_sensors_17 = 0,
        .y_ratio        = 64,   .y_sensors = 9,
        .input_size     = 63,   /* 64, minus one for the report id.  */
        .initialize     = geyser34_initialize,
        .finalize       = geyser34_finalize,
        .base_sample    = base_sample_input_flag,
        .read_sample    = read_sample_2,
        .accumulate     = accumulate_sample_2,
        .reset          = geyser34_deferred_reset,
};

/* Known device models */

#define APPLE_TRACKPAD(PRODUCT, DESCRIPTION, PARAMETERS)                \
        {                                                               \
                .vendor = USB_VENDOR_APPLE,                             \
                .product = (PRODUCT),                                   \
                .description = "Apple " DESCRIPTION " trackpad",        \
                .parameters = (& (PARAMETERS)),                         \
        }

#define POWERBOOK_TRACKPAD(PRODUCT, PARAMETERS)                         \
        APPLE_TRACKPAD(PRODUCT, "PowerBook/iBook", PARAMETERS)
#define MACBOOK_TRACKPAD(PRODUCT, PARAMETERS)                           \
        APPLE_TRACKPAD(PRODUCT, "MacBook/MacBook Pro", PARAMETERS)

static const struct uatp_descriptor uatp_descriptors[] =
{
        POWERBOOK_TRACKPAD(0x020e, fountain_parameters),
        POWERBOOK_TRACKPAD(0x020f, fountain_parameters),
        POWERBOOK_TRACKPAD(0x030a, fountain_parameters),

        POWERBOOK_TRACKPAD(0x030b, geyser_1_parameters),

        POWERBOOK_TRACKPAD(0x0214, geyser_2_parameters),
        POWERBOOK_TRACKPAD(0x0215, geyser_2_parameters),
        POWERBOOK_TRACKPAD(0x0216, geyser_2_parameters),

        MACBOOK_TRACKPAD(0x0217, geyser_3_4_parameters), /* 3 */
        MACBOOK_TRACKPAD(0x0218, geyser_3_4_parameters), /* 3 */
        MACBOOK_TRACKPAD(0x0219, geyser_3_4_parameters), /* 3 */

        MACBOOK_TRACKPAD(0x021a, geyser_3_4_parameters), /* 4 */
        MACBOOK_TRACKPAD(0x021b, geyser_3_4_parameters), /* 4 */
        MACBOOK_TRACKPAD(0x021c, geyser_3_4_parameters), /* 4 */

        MACBOOK_TRACKPAD(0x0229, geyser_3_4_parameters), /* 4 */
        MACBOOK_TRACKPAD(0x022a, geyser_3_4_parameters), /* 4 */
        MACBOOK_TRACKPAD(0x022b, geyser_3_4_parameters), /* 4 */
};

#undef MACBOOK_TRACKPAD
#undef POWERBOOK_TRACKPAD
#undef APPLE_TRACKPAD

/* Miscellaneous utilities */

static const struct uatp_descriptor *
find_uatp_descriptor(const struct uhidev_attach_arg *uha)
{
        unsigned int i;

        for (i = 0; i < __arraycount(uatp_descriptors); i++)
                if ((uha->uiaa->uiaa_vendor == uatp_descriptors[i].vendor) &&
                    (uha->uiaa->uiaa_product == uatp_descriptors[i].product))
                        return &uatp_descriptors[i];

        return NULL;
}

static device_t
uatp_dev(const struct uatp_softc *sc)
{
        return sc->sc_dev;
}

static uint8_t *
uatp_x_sample(struct uatp_softc *sc)
{
        return &sc->sc_sample[0];
}

static uint8_t *
uatp_y_sample(struct uatp_softc *sc)
{
        return &sc->sc_sample[UATP_MAX_X_SENSORS];
}

static int *
uatp_x_acc(struct uatp_softc *sc)
{
        return &sc->sc_acc[0];
}

static int *
uatp_y_acc(struct uatp_softc *sc)
{
        return &sc->sc_acc[UATP_MAX_X_SENSORS];
}

static void
uatp_clear_position(struct uatp_softc *sc)
{
        memset(sc->sc_acc, 0, sizeof(sc->sc_acc));
        sc->sc_motion_timer = 0;
        sc->sc_x_raw = sc->sc_x_smoothed = -1;
        sc->sc_y_raw = sc->sc_y_smoothed = -1;
        sc->sc_z_raw = sc->sc_z_smoothed = -1;
        sc->sc_w_raw = sc->sc_w_smoothed = -1;
        sc->sc_x_remainder = 0;
        sc->sc_y_remainder = 0;
        sc->sc_z_remainder = 0;
        sc->sc_w_remainder = 0;
        sc->sc_track_distance = 0;
}

static unsigned int
uatp_x_sensors(const struct uatp_softc *sc)
{
        if ((0 < sc->sc_knobs.x_sensors) &&
            (sc->sc_knobs.x_sensors <= UATP_MAX_X_SENSORS))
                return sc->sc_knobs.x_sensors;
        else
                return sc->sc_parameters->x_sensors;
}

static unsigned int
uatp_y_sensors(const struct uatp_softc *sc)
{
        if ((0 < sc->sc_knobs.y_sensors) &&
            (sc->sc_knobs.y_sensors <= UATP_MAX_Y_SENSORS))
                return sc->sc_knobs.y_sensors;
        else
                return sc->sc_parameters->y_sensors;
}

static unsigned int
uatp_x_ratio(const struct uatp_softc *sc)
{
        /* XXX Reject bogus values in sysctl.  */
        if ((0 < sc->sc_knobs.x_ratio) &&
            (sc->sc_knobs.x_ratio <= UATP_MAX_X_RATIO))
                return sc->sc_knobs.x_ratio;
        else
                return sc->sc_parameters->x_ratio;
}

static unsigned int
uatp_y_ratio(const struct uatp_softc *sc)
{
        /* XXX Reject bogus values in sysctl.  */
        if ((0 < sc->sc_knobs.y_ratio) &&
            (sc->sc_knobs.y_ratio <= UATP_MAX_Y_RATIO))
                return sc->sc_knobs.y_ratio;
        else
                return sc->sc_parameters->y_ratio;
}

static unsigned int
uatp_old_raw_weight(const struct uatp_softc *sc)
{
        /* XXX Reject bogus values in sysctl.  */
        if (sc->sc_knobs.old_raw_weight <= UATP_MAX_WEIGHT)
                return sc->sc_knobs.old_raw_weight;
        else
                return 0;
}

static unsigned int
uatp_old_smoothed_weight(const struct uatp_softc *sc)
{
        /* XXX Reject bogus values in sysctl.  */
        if (sc->sc_knobs.old_smoothed_weight <= UATP_MAX_WEIGHT)
                return sc->sc_knobs.old_smoothed_weight;
        else
                return 0;
}

static unsigned int
uatp_new_raw_weight(const struct uatp_softc *sc)
{
        /* XXX Reject bogus values in sysctl.  */
        if ((0 < sc->sc_knobs.new_raw_weight) &&
            (sc->sc_knobs.new_raw_weight <= UATP_MAX_WEIGHT))
                return sc->sc_knobs.new_raw_weight;
        else
                return 1;
}

static int
scale_motion(const struct uatp_softc *sc, int delta, int *remainder,
    const unsigned int *multiplier, const unsigned int *divisor)
{
        int product;

        /* XXX Limit the divisor?  */
        if (((*multiplier) == 0) ||
            ((*multiplier) > UATP_MAX_MOTION_MULTIPLIER) ||
            ((*divisor) == 0))
                DPRINTF(sc, UATP_DEBUG_ACCEL,
                    ("bad knobs; %d (+ %d) --> %d, rem 0\n",
                        delta, *remainder, (delta + (*remainder))));
        else
                DPRINTF(sc, UATP_DEBUG_ACCEL,
                    ("scale %d (+ %d) by %u/%u --> %d, rem %d\n",
                        delta, *remainder,
                        (*multiplier), (*divisor),
                        (((delta + (*remainder)) * ((int) (*multiplier)))
                            / ((int) (*divisor))),
                        (((delta + (*remainder)) * ((int) (*multiplier)))
                            % ((int) (*divisor)))));

        if (sc->sc_knobs.motion_remainder)
                delta += *remainder;
        *remainder = 0;

        if (((*multiplier) == 0) ||
            ((*multiplier) > UATP_MAX_MOTION_MULTIPLIER) ||
            ((*divisor) == 0))
                return delta;

        product = (delta * ((int) (*multiplier)));
        *remainder = (product % ((int) (*divisor)));
        return product / ((int) (*divisor));
}

static int
uatp_scale_motion(const struct uatp_softc *sc, int delta, int *remainder)
{
        return scale_motion(sc, delta, remainder,
            &sc->sc_knobs.motion_multiplier,
            &sc->sc_knobs.motion_divisor);
}

static int
uatp_scale_fast_motion(const struct uatp_softc *sc, int delta, int *remainder)
{
        return scale_motion(sc, delta, remainder,
            &sc->sc_knobs.fast_motion_multiplier,
            &sc->sc_knobs.fast_motion_divisor);
}

/* Driver goop */

CFATTACH_DECL2_NEW(uatp, sizeof(struct uatp_softc), uatp_match, uatp_attach,
    uatp_detach, uatp_activate, NULL, uatp_childdet);

static const struct wsmouse_accessops uatp_accessops = {
        .enable = uatp_enable,
        .disable = uatp_disable,
        .ioctl = uatp_ioctl,
};

static int
uatp_match(device_t parent, cfdata_t match, void *aux)
{
        const struct uhidev_attach_arg *uha = aux;
        void *report_descriptor;
        int report_size, input_size;
        const struct uatp_descriptor *uatp_descriptor;

        aprint_debug("%s: vendor 0x%04x, product 0x%04x\n", __func__,
            (unsigned int)uha->uiaa->uiaa_vendor,
            (unsigned int)uha->uiaa->uiaa_product);
        aprint_debug("%s: class 0x%04x, subclass 0x%04x, proto 0x%04x\n",
            __func__,
            (unsigned int)uha->uiaa->uiaa_class,
            (unsigned int)uha->uiaa->uiaa_subclass,
            (unsigned int)uha->uiaa->uiaa_proto);

        uhidev_get_report_desc(uha->parent, &report_descriptor, &report_size);
        input_size = hid_report_size(report_descriptor, report_size,
            hid_input, uha->reportid);
        aprint_debug("%s: reportid %d, input size %d\n", __func__,
            (int)uha->reportid, input_size);

        /*
         * Keyboards, trackpads, and eject buttons share common vendor
         * and product ids, but not protocols: only the trackpad
         * reports a mouse protocol.
         */
        if (uha->uiaa->uiaa_proto != UIPROTO_MOUSE)
                return UMATCH_NONE;

        /* Check for a known vendor/product id.  */
        uatp_descriptor = find_uatp_descriptor(uha);
        if (uatp_descriptor == NULL) {
                aprint_debug("%s: unknown vendor/product id\n", __func__);
                return UMATCH_NONE;
        }

        /* Check for the expected input size.  */
        if ((input_size < 0) ||
            ((unsigned int)input_size !=
                uatp_descriptor->parameters->input_size)) {
                aprint_debug("%s: expected input size %u\n", __func__,
                    uatp_descriptor->parameters->input_size);
                return UMATCH_NONE;
        }

        return UMATCH_VENDOR_PRODUCT_CONF_IFACE;
}

static void
uatp_attach(device_t parent, device_t self, void *aux)
{
        struct uatp_softc *sc = device_private(self);
        const struct uhidev_attach_arg *uha = aux;
        const struct uatp_descriptor *uatp_descriptor;
        void *report_descriptor;
        int report_size, input_size;
        struct wsmousedev_attach_args a;

        sc->sc_dev = self;
        sc->sc_hdev = uha->parent;
        sc->sc_udev = uha->uiaa->uiaa_device;

        /* Identify ourselves to dmesg.  */
        uatp_descriptor = find_uatp_descriptor(uha);
        KASSERT(uatp_descriptor != NULL);
        aprint_normal(": %s\n", uatp_descriptor->description);
        aprint_naive(": %s\n", uatp_descriptor->description);
        aprint_verbose_dev(self,
            "vendor 0x%04x, product 0x%04x, report id %d\n",
            (unsigned int)uha->uiaa->uiaa_vendor,
            (unsigned int)uha->uiaa->uiaa_product,
            uha->reportid);

        uhidev_get_report_desc(uha->parent, &report_descriptor, &report_size);
        input_size = hid_report_size(report_descriptor, report_size, hid_input,
            uha->reportid);
        KASSERT(0 < input_size);
        sc->sc_input_size = input_size;

        /* Initialize model-specific parameters.  */
        sc->sc_parameters = uatp_descriptor->parameters;
        KASSERT((int)sc->sc_parameters->input_size == input_size);
        KASSERT(sc->sc_parameters->x_sensors <= UATP_MAX_X_SENSORS);
        KASSERT(sc->sc_parameters->x_ratio <= UATP_MAX_X_RATIO);
        KASSERT(sc->sc_parameters->y_sensors <= UATP_MAX_Y_SENSORS);
        KASSERT(sc->sc_parameters->y_ratio <= UATP_MAX_Y_RATIO);
        aprint_verbose_dev(self,
            "%u x sensors, scaled by %u for %u points on screen\n",
            sc->sc_parameters->x_sensors, sc->sc_parameters->x_ratio,
            sc->sc_parameters->x_sensors * sc->sc_parameters->x_ratio);
        aprint_verbose_dev(self,
            "%u y sensors, scaled by %u for %u points on screen\n",
            sc->sc_parameters->y_sensors, sc->sc_parameters->y_ratio,
            sc->sc_parameters->y_sensors * sc->sc_parameters->y_ratio);
        if (sc->sc_parameters->initialize)
                sc->sc_parameters->initialize(sc);

        /* Register with pmf.  Nothing special for suspend/resume.  */
        if (!pmf_device_register(self, NULL, NULL))
                aprint_error_dev(self, "couldn't establish power handler\n");

        /* Initialize knobs and create sysctl subtree to tweak them.  */
        sc->sc_knobs = default_knobs;
        uatp_setup_sysctl(sc);

        /* Initialize tapping.  */
        tap_initialize(sc);

        /* Attach wsmouse.  */
        a.accessops = &uatp_accessops;
        a.accesscookie = sc;
        sc->sc_wsmousedev = config_found(self, &a, wsmousedevprint, CFARGS_NONE);
}

/* Sysctl setup */

static void
uatp_setup_sysctl(struct uatp_softc *sc)
{
        int error;

        error = sysctl_createv(&sc->sc_log, 0, NULL, &sc->sc_node, 0,
            CTLTYPE_NODE, device_xname(uatp_dev(sc)),
            SYSCTL_DESCR("uatp configuration knobs"),
            NULL, 0, NULL, 0,
            CTL_HW, CTL_CREATE, CTL_EOL);
        if (error != 0) {
                aprint_error_dev(uatp_dev(sc),
                    "unable to set up sysctl tree hw.%s: %d\n",
                    device_xname(uatp_dev(sc)), error);
                goto err;
        }

#if UATP_DEBUG
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_debug_flags, "debug",
                "uatp(4) debug flags"))
                goto err;
#endif

        /*
         * Button emulation.
         */
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.two_finger_buttons,
                "two_finger_buttons",
                "buttons to emulate with two fingers on trackpad"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.three_finger_buttons,
                "three_finger_buttons",
                "buttons to emulate with three fingers on trackpad"))
                goto err;

#if 0
        /*
         * Edge scrolling.
         */
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.top_edge, "top_edge",
                "width of top edge for edge scrolling"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.bottom_edge,
                "bottom_edge", "width of bottom edge for edge scrolling"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.left_edge, "left_edge",
                "width of left edge for edge scrolling"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.right_edge, "right_edge",
                "width of right edge for edge scrolling"))
                goto err;
#endif

        /*
         * Multifinger tracking.
         */
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.multifinger_track,
                "multifinger_track",
                "0 to ignore multiple fingers, 1 to reset, 2 to scroll"))
                goto err;

        /*
         * Sensor parameters.
         */
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.x_sensors, "x_sensors",
                "number of x sensors"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.x_ratio, "x_ratio",
                "screen width to trackpad width ratio"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.y_sensors, "y_sensors",
                "number of y sensors"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.y_ratio, "y_ratio",
                "screen height to trackpad height ratio"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.sensor_threshold,
                "sensor_threshold", "sensor threshold"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.sensor_normalizer,
                "sensor_normalizer", "sensor normalizer"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.palm_width,
                "palm_width", "lower bound on width/height of palm"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.old_raw_weight,
                "old_raw_weight", "weight of old raw position"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.old_smoothed_weight,
                "old_smoothed_weight", "weight of old smoothed position"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.new_raw_weight,
                "new_raw_weight", "weight of new raw position"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.motion_remainder,
                "motion_remainder", "remember motion division remainder"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.motion_threshold,
                "motion_threshold", "threshold before finger moves cursor"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.motion_multiplier,
                "motion_multiplier", "numerator of motion scale"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.motion_divisor,
                "motion_divisor", "divisor of motion scale"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.fast_motion_threshold,
                "fast_motion_threshold", "threshold before fast motion"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.fast_motion_multiplier,
                "fast_motion_multiplier", "numerator of fast motion scale"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.fast_motion_divisor,
                "fast_motion_divisor", "divisor of fast motion scale"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.fast_per_direction,
                "fast_per_direction", "don't frobnitz the veeblefitzer!"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.motion_delay,
                "motion_delay", "number of packets before motion kicks in"))
                goto err;

        /*
         * Tapping.
         */
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.tap_limit_msec,
                "tap_limit_msec", "milliseconds before a touch is not a tap"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.double_tap_limit_msec,
                "double_tap_limit_msec",
                "milliseconds before a second tap keeps the button down"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.one_finger_tap_buttons,
                "one_finger_tap_buttons", "buttons for one-finger taps"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.two_finger_tap_buttons,
                "two_finger_tap_buttons", "buttons for two-finger taps"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.three_finger_tap_buttons,
                "three_finger_tap_buttons", "buttons for three-finger taps"))
                goto err;
        if (!uatp_setup_sysctl_knob(sc, &sc->sc_knobs.tap_track_distance_limit,
                "tap_track_distance_limit",
                "maximum distance^2 of tracking during tap"))
                goto err;

        return;

err:
        sysctl_teardown(&sc->sc_log);
        sc->sc_node = NULL;
}

static bool
uatp_setup_sysctl_knob(struct uatp_softc *sc, int *ptr, const char *name,
    const char *description)
{
        int error;

        error = sysctl_createv(&sc->sc_log, 0, NULL, NULL, CTLFLAG_READWRITE,
            CTLTYPE_INT, name, SYSCTL_DESCR(description),
            NULL, 0, ptr, 0,
            CTL_HW, sc->sc_node->sysctl_num, CTL_CREATE, CTL_EOL);
        if (error != 0) {
                aprint_error_dev(uatp_dev(sc),
                    "unable to setup sysctl node hw.%s.%s: %d\n",
                    device_xname(uatp_dev(sc)), name, error);
                return false;
        }

        return true;
}

/* More driver goop */

static void
uatp_childdet(device_t self, device_t child)
{
        struct uatp_softc *sc = device_private(self);

        DPRINTF(sc, UATP_DEBUG_MISC, ("detaching child %s\n",
            device_xname(child)));

        /* Our only child is the wsmouse device.  */
        if (child == sc->sc_wsmousedev)
                sc->sc_wsmousedev = NULL;
}

static int
uatp_detach(device_t self, int flags)
{
        struct uatp_softc *sc = device_private(self);
        int error;

        DPRINTF(sc, UATP_DEBUG_MISC, ("detaching with flags %d\n", flags));

        error = config_detach_children(self, flags);
        if (error)
                return error;

        KASSERT((sc->sc_status & UATP_ENABLED) == 0);

        if (sc->sc_parameters->finalize)
                sc->sc_parameters->finalize(sc);

        pmf_device_deregister(self);

        sysctl_teardown(&sc->sc_log);
        sc->sc_node = NULL;

        tap_finalize(sc);

        return 0;
}

static int
uatp_activate(device_t self, enum devact act)
{
        struct uatp_softc *sc = device_private(self);

        DPRINTF(sc, UATP_DEBUG_MISC, ("act %d\n", (int)act));

        if (act != DVACT_DEACTIVATE)
                return EOPNOTSUPP;

        sc->sc_status |= UATP_DYING;

        return 0;
}

/* wsmouse routines */

static int
uatp_enable(void *v)
{
        struct uatp_softc *sc = v;

        DPRINTF(sc, UATP_DEBUG_WSMOUSE, ("enabling wsmouse\n"));

        /* Refuse to enable if we've been deactivated.  */
        if (sc->sc_status & UATP_DYING) {
                DPRINTF(sc, UATP_DEBUG_WSMOUSE, ("busy dying\n"));
                return EIO;
        }

        /* Refuse to enable if we already are enabled.  */
        if (sc->sc_status & UATP_ENABLED) {
                DPRINTF(sc, UATP_DEBUG_WSMOUSE, ("already enabled\n"));
                return EBUSY;
        }

        sc->sc_status |= UATP_ENABLED;
        sc->sc_status &=~ UATP_VALID;
        sc->sc_input_index = 0;
        tap_enable(sc);
        uatp_clear_position(sc);

        DPRINTF(sc, UATP_DEBUG_MISC, ("uhidev_open(%p)\n", sc->sc_hdev));
        return uhidev_open(sc->sc_hdev, &uatp_intr, sc);
}

static void
uatp_disable(void *v)
{
        struct uatp_softc *sc = v;

        DPRINTF(sc, UATP_DEBUG_WSMOUSE, ("disabling wsmouse\n"));

        if (!(sc->sc_status & UATP_ENABLED)) {
                DPRINTF(sc, UATP_DEBUG_WSMOUSE, ("not enabled\n"));
                return;
        }

        tap_disable(sc);
        sc->sc_status &=~ UATP_ENABLED;

        DPRINTF(sc, UATP_DEBUG_MISC, ("uhidev_close(%p)\n", sc->sc_hdev));
        uhidev_close(sc->sc_hdev);
}

static int
uatp_ioctl(void *v, unsigned long cmd, void *data, int flag, struct lwp *p)
{

        DPRINTF((struct uatp_softc*)v, UATP_DEBUG_IOCTL,
            ("cmd %lx, data %p, flag %x, lwp %p\n", cmd, data, flag, p));

        /* XXX Implement any relevant wsmouse(4) ioctls.  */
        return EPASSTHROUGH;
}

/*
 * The Geyser 3 and 4 models talk the generic USB HID mouse protocol by
 * default.  This mode switch makes them give raw sensor data instead
 * so that we can implement tapping, two-finger scrolling, &c.
 */

#define GEYSER34_RAW_MODE               0x04
#define GEYSER34_MODE_REPORT_ID         0
#define GEYSER34_MODE_INTERFACE         0
#define GEYSER34_MODE_PACKET_SIZE       8

static void
geyser34_enable_raw_mode(struct uatp_softc *sc)
{
        uint8_t report[GEYSER34_MODE_PACKET_SIZE];
        usbd_status status;

        DPRINTF(sc, UATP_DEBUG_RESET, ("get feature report\n"));
        status = usbd_get_report(sc->sc_iface0, UHID_FEATURE_REPORT,
            GEYSER34_MODE_REPORT_ID, report, sizeof(report));
        if (status != USBD_NORMAL_COMPLETION) {
                aprint_error_dev(uatp_dev(sc),
                    "error reading feature report: %s\n", usbd_errstr(status));
                return;
        }

#if UATP_DEBUG
        if (sc->sc_debug_flags & UATP_DEBUG_RESET) {
                unsigned int i;
                DPRINTF(sc, UATP_DEBUG_RESET, ("old feature report:"));
                for (i = 0; i < GEYSER34_MODE_PACKET_SIZE; i++)
                        printf(" %02x", (unsigned int)report[i]);
                printf("\n");
                /* Doing this twice is harmless here and lets this be
                 * one ifdef.  */
                report[0] = GEYSER34_RAW_MODE;
                DPRINTF(sc, UATP_DEBUG_RESET, ("new feature report:"));
                for (i = 0; i < GEYSER34_MODE_PACKET_SIZE; i++)
                        printf(" %02x", (unsigned int)report[i]);
                printf("\n");
        }
#endif

        report[0] = GEYSER34_RAW_MODE;

        DPRINTF(sc, UATP_DEBUG_RESET, ("set feature report\n"));
        status = usbd_set_report(sc->sc_iface0, UHID_FEATURE_REPORT,
            GEYSER34_MODE_REPORT_ID, report, sizeof(report));
        if (status != USBD_NORMAL_COMPLETION) {
                aprint_error_dev(uatp_dev(sc),
                    "error writing feature report: %s\n", usbd_errstr(status));
                return;
        }
}

/*
 * The Geyser 3 and 4 need to be reset periodically after we detect a
 * continual flow of spurious interrupts.  We use a USB task for this.
 */

static void
geyser34_initialize(struct uatp_softc *sc)
{
        usbd_status err __diagused;

        DPRINTF(sc, UATP_DEBUG_MISC, ("initializing\n"));
        err = usbd_device2interface_handle(sc->sc_udev, 0, &sc->sc_iface0);
        KASSERT(err == 0);      /* always an interface 0 if attached */
        geyser34_enable_raw_mode(sc);
        usb_init_task(&sc->sc_reset_task, &geyser34_reset_task, sc, 0);
}

static void
geyser34_finalize(struct uatp_softc *sc)
{

        DPRINTF(sc, UATP_DEBUG_MISC, ("finalizing\n"));
        usb_rem_task_wait(sc->sc_udev, &sc->sc_reset_task, USB_TASKQ_DRIVER,
            NULL);
}

static void
geyser34_deferred_reset(struct uatp_softc *sc)
{

        DPRINTF(sc, UATP_DEBUG_RESET, ("deferring reset\n"));
        usb_add_task(sc->sc_udev, &sc->sc_reset_task, USB_TASKQ_DRIVER);
}

static void
geyser34_reset_task(void *arg)
{
        struct uatp_softc *sc = arg;

        DPRINTF(sc, UATP_DEBUG_RESET, ("resetting\n"));

        /* Reset by putting it into raw mode.  Not sure why.  */
        geyser34_enable_raw_mode(sc);
}

/* Interrupt handler */

static void
uatp_intr(void *cookie, void *ibuf, unsigned int len)
{
        struct uatp_softc *sc = cookie;
        uint8_t *input;
        int dx, dy, dz, dw;
        uint32_t buttons;

        DPRINTF(sc, UATP_DEBUG_INTR, ("softc %p, ibuf %p, len %u\n",
            sc, ibuf, len));

        /*
         * Some devices break packets up into chunks, so we accumulate
         * input up to the expected packet length, or if it would
         * overflow, discard the whole packet and start over.
         */
        if (sc->sc_input_size < len) {
                aprint_error_dev(uatp_dev(sc),
                    "discarding %u-byte input packet\n", len);
                sc->sc_input_index = 0;
                return;
        } else if (sc->sc_input_size < (sc->sc_input_index + len)) {
                aprint_error_dev(uatp_dev(sc), "discarding %u-byte input\n",
                    (sc->sc_input_index + len));
                sc->sc_input_index = 0;
                return;
        } else if (sc->sc_input_size == 81 && len == 17 &&
            sc->sc_input_index != 64) {
                /*
                 * Quirk of Fountain and Geyser 1 devices: a 17-byte
                 * packet seems to mean the last one, but sometimes we
                 * get desynchronized, so drop this one and start over
                 * if we see a 17-byte packet that's not at the end.
                 */
                aprint_error_dev(uatp_dev(sc),
                    "discarding 17-byte nonterminal input at %u\n",
                    sc->sc_input_index);
                sc->sc_input_index = 0;
                return;
        }

#if UATP_DEBUG
        if (sc->sc_debug_flags & UATP_DEBUG_INTR) {
                unsigned int i;
                uint8_t *bytes = ibuf;
                DPRINTF(sc, UATP_DEBUG_INTR, ("raw"));
                for (i = 0; i < len; i++)
                        printf(" %02x", (unsigned int)bytes[i]);
                printf("\n");
        }
#endif

        memcpy(&sc->sc_input[sc->sc_input_index], ibuf, len);
        sc->sc_input_index += len;
        if (sc->sc_input_index != sc->sc_input_size) {
                /* Wait until packet is complete.  */
                DPRINTF(sc, UATP_DEBUG_INTR, ("partial packet: %u bytes\n",
                    len));
                return;
        }

        /* Clear the buffer and process the now complete packet.  */
        sc->sc_input_index = 0;
        input = sc->sc_input;

        /* The last byte's first bit is set iff the button is pressed.
         * XXX Left button should have a name.  */
        buttons = ((input[sc->sc_input_size - 1] & UATP_STATUS_BUTTON)
            ? 1 : 0);

        /* Read the sample.  */
        memset(uatp_x_sample(sc), 0, UATP_MAX_X_SENSORS);
        memset(uatp_y_sample(sc), 0, UATP_MAX_Y_SENSORS);
        sc->sc_parameters->read_sample(uatp_x_sample(sc), uatp_y_sample(sc),
            input);

#if UATP_DEBUG
        if (sc->sc_debug_flags & UATP_DEBUG_INTR) {
                unsigned int i;
                DPRINTF(sc, UATP_DEBUG_INTR, ("x sensors"));
                for (i = 0; i < uatp_x_sensors(sc); i++)
                        printf(" %02x", (unsigned int)uatp_x_sample(sc)[i]);
                printf("\n");
                DPRINTF(sc, UATP_DEBUG_INTR, ("y sensors"));
                for (i = 0; i < uatp_y_sensors(sc); i++)
                        printf(" %02x", (unsigned int)uatp_y_sample(sc)[i]);
                printf("\n");
        } else if ((sc->sc_debug_flags & UATP_DEBUG_STATUS) &&
                (input[sc->sc_input_size - 1] &~
                    (UATP_STATUS_BUTTON | UATP_STATUS_BASE |
                        UATP_STATUS_POST_RESET)))
                DPRINTF(sc, UATP_DEBUG_STATUS, ("status byte: %02x\n",
                    input[sc->sc_input_size - 1]));
#endif

        /*
         * If this is a base sample, initialize the state to interpret
         * subsequent samples relative to it, and stop here.
         */
        if (sc->sc_parameters->base_sample(sc, input)) {
                DPRINTF(sc, UATP_DEBUG_PARSE,
                    ("base sample, buttons %"PRIx32"\n", buttons));
                /* XXX Should the valid bit ever be reset?  */
                sc->sc_status |= UATP_VALID;
                uatp_clear_position(sc);
                memcpy(sc->sc_base, sc->sc_sample, sizeof(sc->sc_base));
                /* XXX Perform 17" size detection like Linux?  */
                return;
        }

        /* If not, accumulate the change in the sensors.  */
        sc->sc_parameters->accumulate(sc);

#if UATP_DEBUG
        if (sc->sc_debug_flags & UATP_DEBUG_ACCUMULATE) {
                unsigned int i;
                DPRINTF(sc, UATP_DEBUG_ACCUMULATE, ("accumulated x state:"));
                for (i = 0; i < uatp_x_sensors(sc); i++)
                        printf(" %02x", (unsigned int)uatp_x_acc(sc)[i]);
                printf("\n");
                DPRINTF(sc, UATP_DEBUG_ACCUMULATE, ("accumulated y state:"));
                for (i = 0; i < uatp_y_sensors(sc); i++)
                        printf(" %02x", (unsigned int)uatp_y_acc(sc)[i]);
                printf("\n");
        }
#endif

        /* Compute the change in coordinates and buttons.  */
        dx = dy = dz = dw = 0;
        if ((!interpret_input(sc, &dx, &dy, &dz, &dw, &buttons)) &&
            /* If there's no input because we're releasing a button,
             * then it's not spurious.  XXX Mutex?  */
            (sc->sc_buttons == 0)) {
                DPRINTF(sc, UATP_DEBUG_SPURINTR, ("spurious interrupt\n"));
                if (sc->sc_parameters->reset)
                        sc->sc_parameters->reset(sc);
                return;
        }

        /* Report to wsmouse.  */
        DPRINTF(sc, UATP_DEBUG_INTR,
            ("buttons %"PRIx32", dx %d, dy %d, dz %d, dw %d\n",
                buttons, dx, dy, dz, dw));
        mutex_enter(&sc->sc_tap_mutex);
        uatp_input(sc, buttons, dx, dy, dz, dw);
        mutex_exit(&sc->sc_tap_mutex);
}

/*
 * Different ways to discern the base sample initializing the state.
 * `base_sample_softc_flag' uses a state flag stored in the softc;
 * `base_sample_input_flag' checks a flag at the end of the input
 * packet.
 */

static bool
base_sample_softc_flag(const struct uatp_softc *sc, const uint8_t *input)
{
        return !(sc->sc_status & UATP_VALID);
}

static bool
base_sample_input_flag(const struct uatp_softc *sc, const uint8_t *input)
{
        /* XXX Should we also check the valid flag?  */
        return !!(input[sc->sc_input_size - 1] & UATP_STATUS_BASE);
}

/*
 * Pick apart the horizontal sensors from the vertical sensors.
 * Different models interleave them in different orders.
 */

static void
read_sample_1(uint8_t *x, uint8_t *y, const uint8_t *input)
{
        unsigned int i;

        for (i = 0; i < 8; i++) {
                x[i] = input[5 * i + 2];
                x[i + 8] = input[5 * i + 4];
                x[i + 16] = input[5 * i + 42];
                if (i < 2)
                        x[i + 24] = input[5 * i + 44];

                y[i] = input[5 * i + 1];
                y[i + 8] = input[5 * i + 3];
        }
}

static void
read_sample_2(uint8_t *x, uint8_t *y, const uint8_t *input)
{
        unsigned int i, j;

        for (i = 0, j = 19; i < 20; i += 2, j += 3) {
                x[i] = input[j];
                x[i + 1] = input[j + 1];
        }

        for (i = 0, j = 1; i < 9; i += 2, j += 3) {
                y[i] = input[j];
                y[i + 1] = input[j + 1];
        }
}

static void
accumulate_sample_1(struct uatp_softc *sc)
{
        unsigned int i;

        for (i = 0; i < UATP_SENSORS; i++) {
                sc->sc_acc[i] += (int8_t)(sc->sc_sample[i] - sc->sc_base[i]);
                if (sc->sc_acc[i] < 0) {
                        sc->sc_acc[i] = 0;
                } else if (UATP_MAX_ACC < sc->sc_acc[i]) {
                        DPRINTF(sc, UATP_DEBUG_ACCUMULATE,
                            ("overflow %d\n", sc->sc_acc[i]));
                        sc->sc_acc[i] = UATP_MAX_ACC;
                }
        }

        memcpy(sc->sc_base, sc->sc_sample, sizeof(sc->sc_base));
}

static void
accumulate_sample_2(struct uatp_softc *sc)
{
        unsigned int i;

        for (i = 0; i < UATP_SENSORS; i++) {
                sc->sc_acc[i] = (int8_t)(sc->sc_sample[i] - sc->sc_base[i]);
                if (sc->sc_acc[i] < -0x80) {
                        DPRINTF(sc, UATP_DEBUG_ACCUMULATE,
                            ("underflow %u - %u = %d\n",
                                (unsigned int)sc->sc_sample[i],
                                (unsigned int)sc->sc_base[i],
                                sc->sc_acc[i]));
                        sc->sc_acc[i] += 0x100;
                }
                if (0x7f < sc->sc_acc[i]) {
                        DPRINTF(sc, UATP_DEBUG_ACCUMULATE,
                            ("overflow %u - %u = %d\n",
                                (unsigned int)sc->sc_sample[i],
                                (unsigned int)sc->sc_base[i],
                                sc->sc_acc[i]));
                        sc->sc_acc[i] -= 0x100;
                }
                if (sc->sc_acc[i] < 0)
                        sc->sc_acc[i] = 0;
        }
}

/*
 * Report input to wsmouse, if there is anything interesting to report.
 * We must take into consideration the current tap-and-drag button
 * state.
 */

static void
uatp_input(struct uatp_softc *sc, uint32_t buttons,
    int dx, int dy, int dz, int dw)
{
        uint32_t all_buttons;

        KASSERT(mutex_owned(&sc->sc_tap_mutex));
        all_buttons = buttons | uatp_tapped_buttons(sc);

        if ((sc->sc_wsmousedev != NULL) &&
            ((dx != 0) || (dy != 0) || (dz != 0) || (dw != 0) ||
                (all_buttons != sc->sc_all_buttons))) {
                int s = spltty();
                DPRINTF(sc, UATP_DEBUG_WSMOUSE, ("wsmouse input:"
                    " buttons %"PRIx32", dx %d, dy %d, dz %d, dw %d\n",
                    all_buttons, dx, -dy, dz, -dw));
                wsmouse_input(sc->sc_wsmousedev, all_buttons, dx, -dy, dz, -dw,
                    WSMOUSE_INPUT_DELTA);
                splx(s);
        }
        sc->sc_buttons = buttons;
        sc->sc_all_buttons = all_buttons;
}

/*
 * Interpret the current tap state to decide whether the tap buttons
 * are currently pressed.
 */

static uint32_t
uatp_tapped_buttons(struct uatp_softc *sc)
{
        KASSERT(mutex_owned(&sc->sc_tap_mutex));
        switch (sc->sc_tap_state) {
        case TAP_STATE_INITIAL:
        case TAP_STATE_TAPPING:
                return 0;

        case TAP_STATE_TAPPED:
        case TAP_STATE_DOUBLE_TAPPING:
        case TAP_STATE_DRAGGING_DOWN:
        case TAP_STATE_DRAGGING_UP:
        case TAP_STATE_TAPPING_IN_DRAG:
                CHECK((0 < sc->sc_tapped_fingers), return 0);
                switch (sc->sc_tapped_fingers) {
                case 1: return sc->sc_knobs.one_finger_tap_buttons;
                case 2: return sc->sc_knobs.two_finger_tap_buttons;
                case 3:
                default: return sc->sc_knobs.three_finger_tap_buttons;
                }

        default:
                aprint_error_dev(uatp_dev(sc), "%s: invalid tap state: %d\n",
                    __func__, sc->sc_tap_state);
                return 0;
        }
}

/*
 * Interpret the current input state to find a difference in all the
 * relevant coordinates and buttons to pass on to wsmouse, and update
 * any internal driver state necessary to interpret subsequent input
 * relative to this one.
 */

static bool
interpret_input(struct uatp_softc *sc, int *dx, int *dy, int *dz, int *dw,
    uint32_t *buttons)
{
        unsigned int x_pressure, x_raw, x_fingers;
        unsigned int y_pressure, y_raw, y_fingers;
        unsigned int fingers;

        x_pressure = interpret_dimension(sc, uatp_x_acc(sc),
            uatp_x_sensors(sc), uatp_x_ratio(sc), &x_raw, &x_fingers);
        y_pressure = interpret_dimension(sc, uatp_y_acc(sc),
            uatp_y_sensors(sc), uatp_y_ratio(sc), &y_raw, &y_fingers);

        DPRINTF(sc, UATP_DEBUG_PARSE,
            ("x %u @ %u, %uf; y %u @ %u, %uf; buttons %"PRIx32"\n",
                x_pressure, x_raw, x_fingers,
                y_pressure, y_raw, y_fingers,
                *buttons));

        if ((x_pressure == 0) && (y_pressure == 0)) {
                bool ok;
                /* No fingers: clear position and maybe report a tap.  */
                DPRINTF(sc, UATP_DEBUG_INTR,
                    ("no position detected; clearing position\n"));
                if (*buttons == 0) {
                        ok = tap_released(sc);
                } else {
                        tap_reset(sc);
                        /* Button pressed: interrupt is not spurious.  */
                        ok = true;
                }
                /*
                 * Don't clear the position until after tap_released,
                 * which needs to know the track distance.
                 */
                uatp_clear_position(sc);
                return ok;
        } else if ((x_pressure == 0) || (y_pressure == 0)) {
                /* XXX What to do here?  */
                DPRINTF(sc, UATP_DEBUG_INTR,
                    ("pressure in only one dimension; ignoring\n"));
                return true;
        } else if ((x_pressure == 1) && (y_pressure == 1)) {
                fingers = uimax(x_fingers, y_fingers);
                CHECK((0 < fingers), return false);
                if (*buttons == 0)
                        tap_touched(sc, fingers);
                else if (fingers == 1)
                        tap_reset(sc);
                else            /* Multiple fingers, button pressed.  */
                        *buttons = emulated_buttons(sc, fingers);
                update_position(sc, fingers, x_raw, y_raw, dx, dy, dz, dw);
                return true;
        } else {
                /* Palm detected in either or both of the dimensions.  */
                DPRINTF(sc, UATP_DEBUG_INTR, ("palm detected; ignoring\n"));
                return true;
        }
}

/*
 * Interpret the accumulated sensor state along one dimension to find
 * the number, mean position, and pressure of fingers.  Returns 0 to
 * indicate no pressure, returns 1 and sets *position and *fingers to
 * indicate fingers, and returns 2 to indicate palm.
 *
 * XXX Give symbolic names to the return values.
 */

static unsigned int
interpret_dimension(struct uatp_softc *sc, const int *acc,
    unsigned int n_sensors, unsigned int ratio,
    unsigned int *position, unsigned int *fingers)
{
        unsigned int i, v, n_fingers, sum;
        unsigned int total[UATP_MAX_SENSORS];
        unsigned int weighted[UATP_MAX_SENSORS];
        unsigned int sensor_threshold = sc->sc_knobs.sensor_threshold;
        unsigned int sensor_normalizer = sc->sc_knobs.sensor_normalizer;
        unsigned int width = 0; /* GCC is not smart enough.  */
        unsigned int palm_width = sc->sc_knobs.palm_width;
        enum { none, nondecreasing, decreasing } state = none;

        if (sensor_threshold < sensor_normalizer)
                sensor_normalizer = sensor_threshold;
        if (palm_width == 0)    /* Effectively disable palm detection.  */
                palm_width = UATP_MAX_POSITION;

#define CHECK_(condition) CHECK(condition, return 0)

        /*
         * Arithmetic bounds:
         * . n_sensors is at most UATP_MAX_SENSORS,
         * . n_fingers is at most UATP_MAX_SENSORS,
         * . i is at most UATP_MAX_SENSORS,
         * . sc->sc_acc[i] is at most UATP_MAX_ACC,
         * . i * sc->sc_acc[i] is at most UATP_MAX_SENSORS * UATP_MAX_ACC,
         * . each total[j] is at most UATP_MAX_SENSORS * UATP_MAX_ACC,
         * . each weighted[j] is at most UATP_MAX_SENSORS^2 * UATP_MAX_ACC,
         * . ratio is at most UATP_MAX_RATIO,
         * . each weighted[j] * ratio is at most
         *     UATP_MAX_SENSORS^2 * UATP_MAX_ACC * UATP_MAX_RATIO,
         *   which is #x5fa0000 with the current values of the constants,
         *   and
         * . the sum of the positions is at most
         *     UATP_MAX_SENSORS * UATP_MAX_POSITION,
         *   which is #x60000 with the current values of the constants.
         * Hence all of the arithmetic here fits in int (and thus also
         * unsigned int).  If you change the constants, though, you
         * must update the analysis.
         */
        __CTASSERT(0x5fa0000 == (UATP_MAX_SENSORS * UATP_MAX_SENSORS *
                UATP_MAX_ACC * UATP_MAX_RATIO));
        __CTASSERT(0x60000 == (UATP_MAX_SENSORS * UATP_MAX_POSITION));
        CHECK_(n_sensors <= UATP_MAX_SENSORS);
        CHECK_(ratio <= UATP_MAX_RATIO);

        /*
         * Detect each finger by looking for a consecutive sequence of
         * increasing and then decreasing pressures above the sensor
         * threshold.  Compute the finger's position as the weighted
         * average of positions, weighted by the pressure at that
         * position.  Finally, return the average finger position.
         */

        n_fingers = 0;
        memset(weighted, 0, sizeof(weighted));
        memset(total, 0, sizeof(total));

        for (i = 0; i < n_sensors; i++) {
                CHECK_(0 <= acc[i]);
                v = acc[i];

                /* Ignore values outside a sensible interval.  */
                if (v <= sensor_threshold) {
                        state = none;
                        continue;
                } else if (UATP_MAX_ACC < v) {
                        aprint_verbose_dev(uatp_dev(sc),
                            "ignoring large accumulated sensor state: %u\n",
                            v);
                        continue;
                }

                switch (state) {
                case none:
                        n_fingers += 1;
                        CHECK_(n_fingers <= n_sensors);
                        state = nondecreasing;
                        width = 1;
                        break;

                case nondecreasing:
                case decreasing:
                        CHECK_(0 < i);
                        CHECK_(0 <= acc[i - 1]);
                        width += 1;
                        if (palm_width <= (width * ratio)) {
                                DPRINTF(sc, UATP_DEBUG_PALM,
                                    ("palm detected\n"));
                                return 2;
                        } else if ((state == nondecreasing) &&
                            ((unsigned int)acc[i - 1] > v)) {
                                state = decreasing;
                        } else if ((state == decreasing) &&
                            ((unsigned int)acc[i - 1] < v)) {
                                n_fingers += 1;
                                CHECK_(n_fingers <= n_sensors);
                                state = nondecreasing;
                                width = 1;
                        }
                        break;

                default:
                        aprint_error_dev(uatp_dev(sc),
                            "bad finger detection state: %d", state);
                        return 0;
                }

                v -= sensor_normalizer;
                total[n_fingers - 1] += v;
                weighted[n_fingers - 1] += (i * v);
                CHECK_(total[n_fingers - 1] <=
                    (UATP_MAX_SENSORS * UATP_MAX_ACC));
                CHECK_(weighted[n_fingers - 1] <=
                    (UATP_MAX_SENSORS * UATP_MAX_SENSORS * UATP_MAX_ACC));
        }

        if (n_fingers == 0)
                return 0;

        sum = 0;
        for (i = 0; i < n_fingers; i++) {
                DPRINTF(sc, UATP_DEBUG_PARSE,
                    ("finger at %u\n", ((weighted[i] * ratio) / total[i])));
                sum += ((weighted[i] * ratio) / total[i]);
                CHECK_(sum <= UATP_MAX_SENSORS * UATP_MAX_POSITION);
        }

        *fingers = n_fingers;
        *position = (sum / n_fingers);
        return 1;

#undef CHECK_
}

/* Tapping */

/*
 * There is a very hairy state machine for detecting taps.  At every
 * touch, we record the maximum number of fingers touched, and don't
 * reset it to zero until the finger is released.
 *
 * INITIAL STATE
 * (no tapping fingers; no tapped fingers)
 * - On touch, go to TAPPING STATE.
 * - On any other input, remain in INITIAL STATE.
 *
 * TAPPING STATE: Finger touched; might be tap.
 * (tapping fingers; no tapped fingers)
 * - On release within the tap limit, go to TAPPED STATE.
 * - On release after the tap limit, go to INITIAL STATE.
 * - On any other input, remain in TAPPING STATE.
 *
 * TAPPED STATE: Finger recently tapped, and might double-tap.
 * (no tapping fingers; tapped fingers)
 * - On touch within the double-tap limit, go to DOUBLE-TAPPING STATE.
 * - On touch after the double-tap limit, go to TAPPING STATE.
 * - On no event after the double-tap limit, go to INITIAL STATE.
 * - On any other input, remain in TAPPED STATE.
 *
 * DOUBLE-TAPPING STATE: Finger touched soon after tap; might be double-tap.
 * (tapping fingers; tapped fingers)
 * - On release within the tap limit, release button and go to TAPPED STATE.
 * - On release after the tap limit, go to DRAGGING UP STATE.
 * - On touch after the tap limit, go to DRAGGING DOWN STATE.
 * - On any other input, remain in DOUBLE-TAPPING STATE.
 *
 * DRAGGING DOWN STATE: Finger has double-tapped and is dragging, not tapping.
 * (no tapping fingers; tapped fingers)
 * - On release, go to DRAGGING UP STATE.
 * - On any other input, remain in DRAGGING DOWN STATE.
 *
 * DRAGGING UP STATE: Finger has double-tapped and is up.
 * (no tapping fingers; tapped fingers)
 * - On touch, go to TAPPING IN DRAG STATE.
 * - On any other input, remain in DRAGGING UP STATE.
 *
 * TAPPING IN DRAG STATE: Tap-dancing while cross-dressed.
 * (tapping fingers; tapped fingers)
 * - On release within the tap limit, go to TAPPED STATE.
 * - On release after the tap limit, go to DRAGGING UP STATE.
 * - On any other input, remain in TAPPING IN DRAG STATE.
 *
 * Warning:  The graph of states is split into two components, those
 * with tapped fingers and those without.  The only path from any state
 * without tapped fingers to a state with tapped fingers must pass
 * through TAPPED STATE.  Also, the only transitions into TAPPED STATE
 * must be from states with tapping fingers, which become the tapped
 * fingers.  If you edit the state machine, you must either preserve
 * these properties, or globally transform the state machine to avoid
 * the bad consequences of violating these properties.
 */

static void
uatp_tap_limit(const struct uatp_softc *sc, struct timeval *limit)
{
        unsigned int msec = sc->sc_knobs.tap_limit_msec;
        limit->tv_sec = 0;
        limit->tv_usec = ((msec < 1000) ? (1000 * msec) : 100000);
}

#if UATP_DEBUG

#  define TAP_DEBUG_PRE(sc)     tap_debug((sc), __func__, "")
#  define TAP_DEBUG_POST(sc)    tap_debug((sc), __func__, " ->")

static void
tap_debug(struct uatp_softc *sc, const char *caller, const char *prefix)
{
        char buffer[128];
        const char *state;

        KASSERT(mutex_owned(&sc->sc_tap_mutex));
        switch (sc->sc_tap_state) {
        case TAP_STATE_INITIAL:         state = "initial";              break;
        case TAP_STATE_TAPPING:         state = "tapping";              break;
        case TAP_STATE_TAPPED:          state = "tapped";               break;
        case TAP_STATE_DOUBLE_TAPPING:  state = "double-tapping";       break;
        case TAP_STATE_DRAGGING_DOWN:   state = "dragging-down";        break;
        case TAP_STATE_DRAGGING_UP:     state = "dragging-up";          break;
        case TAP_STATE_TAPPING_IN_DRAG: state = "tapping-in-drag";      break;
        default:
                snprintf(buffer, sizeof(buffer), "unknown (%d)",
                    sc->sc_tap_state);
                state = buffer;
                break;
        }

        DPRINTF(sc, UATP_DEBUG_TAP,
            ("%s:%s state %s, %u tapping, %u tapped\n",
                caller, prefix, state,
                sc->sc_tapping_fingers, sc->sc_tapped_fingers));
}

#else   /* !UATP_DEBUG */

#  define TAP_DEBUG_PRE(sc)     do {} while (0)
#  define TAP_DEBUG_POST(sc)    do {} while (0)

#endif

static void
tap_initialize(struct uatp_softc *sc)
{
        callout_init(&sc->sc_untap_callout, 0);
        callout_setfunc(&sc->sc_untap_callout, untap_callout, sc);
        mutex_init(&sc->sc_tap_mutex, MUTEX_DEFAULT, IPL_SOFTUSB);
}

static void
tap_finalize(struct uatp_softc *sc)
{
        /* XXX Can the callout still be scheduled here?  */
        callout_destroy(&sc->sc_untap_callout);
        mutex_destroy(&sc->sc_tap_mutex);
}

static void
tap_enable(struct uatp_softc *sc)
{
        mutex_enter(&sc->sc_tap_mutex);
        tap_transition_initial(sc);
        sc->sc_buttons = 0;     /* XXX Not the right place?  */
        sc->sc_all_buttons = 0;
        mutex_exit(&sc->sc_tap_mutex);
}

static void
tap_disable(struct uatp_softc *sc)
{
        /* Reset tapping, and wait for any callouts to complete.  */
        tap_reset_wait(sc);
}

/*
 * Reset tap state.  If the untap callout has just fired, it may signal
 * a harmless button release event before this returns.
 */

static void
tap_reset(struct uatp_softc *sc)
{

        callout_stop(&sc->sc_untap_callout);
        mutex_enter(&sc->sc_tap_mutex);
        tap_transition_initial(sc);
        mutex_exit(&sc->sc_tap_mutex);
}

/* Reset, but don't return until the callout is done running.  */

static void
tap_reset_wait(struct uatp_softc *sc)
{

        callout_halt(&sc->sc_untap_callout, NULL);
        mutex_enter(&sc->sc_tap_mutex);
        tap_transition_initial(sc);
        mutex_exit(&sc->sc_tap_mutex);
}

static const struct timeval zero_timeval;

static void
tap_transition(struct uatp_softc *sc, enum uatp_tap_state tap_state,
    const struct timeval *start_time,
    unsigned int tapping_fingers, unsigned int tapped_fingers)
{
        KASSERT(mutex_owned(&sc->sc_tap_mutex));
        sc->sc_tap_state = tap_state;
        sc->sc_tap_timer = *start_time;
        sc->sc_tapping_fingers = tapping_fingers;
        sc->sc_tapped_fingers = tapped_fingers;
}

static void
tap_transition_initial(struct uatp_softc *sc)
{
        /*
         * No checks.  This state is always kosher, and sometimes a
         * fallback in case of failure.
         */
        tap_transition(sc, TAP_STATE_INITIAL, &zero_timeval, 0, 0);
}

/* Touch transitions */

static void
tap_transition_tapping(struct uatp_softc *sc, const struct timeval *start_time,
    unsigned int fingers)
{
        CHECK((sc->sc_tapping_fingers <= fingers),
            do { tap_transition_initial(sc); return; } while (0));
        tap_transition(sc, TAP_STATE_TAPPING, start_time, fingers, 0);
}

static void
tap_transition_double_tapping(struct uatp_softc *sc,
    const struct timeval *start_time, unsigned int fingers)
{
        CHECK((sc->sc_tapping_fingers <= fingers),
            do { tap_transition_initial(sc); return; } while (0));
        CHECK((0 < sc->sc_tapped_fingers),
            do { tap_transition_initial(sc); return; } while (0));
        tap_transition(sc, TAP_STATE_DOUBLE_TAPPING, start_time, fingers,
            sc->sc_tapped_fingers);
}

static void
tap_transition_dragging_down(struct uatp_softc *sc)
{
        CHECK((0 < sc->sc_tapped_fingers),
            do { tap_transition_initial(sc); return; } while (0));
        tap_transition(sc, TAP_STATE_DRAGGING_DOWN, &zero_timeval, 0,
            sc->sc_tapped_fingers);
}

static void
tap_transition_tapping_in_drag(struct uatp_softc *sc,
    const struct timeval *start_time, unsigned int fingers)
{
        CHECK((sc->sc_tapping_fingers <= fingers),
            do { tap_transition_initial(sc); return; } while (0));
        CHECK((0 < sc->sc_tapped_fingers),
            do { tap_transition_initial(sc); return; } while (0));
        tap_transition(sc, TAP_STATE_TAPPING_IN_DRAG, start_time, fingers,
            sc->sc_tapped_fingers);
}

/* Release transitions */

static void
tap_transition_tapped(struct uatp_softc *sc, const struct timeval *start_time)
{
        /*
         * The fingers that were tapping -- of which there must have
         * been at least one -- are now the fingers that have tapped,
         * and there are no longer fingers tapping.
         */
        CHECK((0 < sc->sc_tapping_fingers),
            do { tap_transition_initial(sc); return; } while (0));
        tap_transition(sc, TAP_STATE_TAPPED, start_time, 0,
            sc->sc_tapping_fingers);
        schedule_untap(sc);
}

static void
tap_transition_dragging_up(struct uatp_softc *sc)
{
        CHECK((0 < sc->sc_tapped_fingers),
            do { tap_transition_initial(sc); return; } while (0));
        tap_transition(sc, TAP_STATE_DRAGGING_UP, &zero_timeval, 0,
            sc->sc_tapped_fingers);
}

static void
tap_touched(struct uatp_softc *sc, unsigned int fingers)
{
        struct timeval now, diff, limit;

        CHECK((0 < fingers), return);
        callout_stop(&sc->sc_untap_callout);
        mutex_enter(&sc->sc_tap_mutex);
        TAP_DEBUG_PRE(sc);
        /*
         * Guarantee that the number of tapping fingers never decreases
         * except when it is reset to zero on release.
         */
        if (fingers < sc->sc_tapping_fingers)
                fingers = sc->sc_tapping_fingers;
        switch (sc->sc_tap_state) {
        case TAP_STATE_INITIAL:
                getmicrouptime(&now);
                tap_transition_tapping(sc, &now, fingers);
                break;

        case TAP_STATE_TAPPING:
                /*
                 * Number of fingers may have increased, so transition
                 * even though we're already in TAPPING.
                 */
                tap_transition_tapping(sc, &sc->sc_tap_timer, fingers);
                break;

        case TAP_STATE_TAPPED:
                getmicrouptime(&now);
                /*
                 * If the double-tap time limit has passed, it's the
                 * callout's responsibility to handle that event, so we
                 * assume the limit has not passed yet.
                 */
                tap_transition_double_tapping(sc, &now, fingers);
                break;

        case TAP_STATE_DOUBLE_TAPPING:
                getmicrouptime(&now);
                timersub(&now, &sc->sc_tap_timer, &diff);
                uatp_tap_limit(sc, &limit);
                if (timercmp(&diff, &limit, >) ||
                    (sc->sc_track_distance >
                        sc->sc_knobs.tap_track_distance_limit))
                        tap_transition_dragging_down(sc);
                break;

        case TAP_STATE_DRAGGING_DOWN:
                break;

        case TAP_STATE_DRAGGING_UP:
                getmicrouptime(&now);
                tap_transition_tapping_in_drag(sc, &now, fingers);
                break;

        case TAP_STATE_TAPPING_IN_DRAG:
                /*
                 * Number of fingers may have increased, so transition
                 * even though we're already in TAPPING IN DRAG.
                 */
                tap_transition_tapping_in_drag(sc, &sc->sc_tap_timer, fingers);
                break;

        default:
                aprint_error_dev(uatp_dev(sc), "%s: invalid tap state: %d\n",
                    __func__, sc->sc_tap_state);
                tap_transition_initial(sc);
                break;
        }
        TAP_DEBUG_POST(sc);
        mutex_exit(&sc->sc_tap_mutex);
}

static bool
tap_released(struct uatp_softc *sc)
{
        struct timeval now, diff, limit;
        void (*non_tapped_transition)(struct uatp_softc *);
        bool ok, temporary_release;

        mutex_enter(&sc->sc_tap_mutex);
        TAP_DEBUG_PRE(sc);
        switch (sc->sc_tap_state) {
        case TAP_STATE_INITIAL:
        case TAP_STATE_TAPPED:
        case TAP_STATE_DRAGGING_UP:
                /* Spurious interrupt: fingers are already off.  */
                ok = false;
                break;

        case TAP_STATE_TAPPING:
                temporary_release = false;
                non_tapped_transition = &tap_transition_initial;
                goto maybe_tap;

        case TAP_STATE_DOUBLE_TAPPING:
                temporary_release = true;
                non_tapped_transition = &tap_transition_dragging_up;
                goto maybe_tap;

        case TAP_STATE_TAPPING_IN_DRAG:
                temporary_release = false;
                non_tapped_transition = &tap_transition_dragging_up;
                goto maybe_tap;

        maybe_tap:
                getmicrouptime(&now);
                timersub(&now, &sc->sc_tap_timer, &diff);
                uatp_tap_limit(sc, &limit);
                if (timercmp(&diff, &limit, <=) &&
                    (sc->sc_track_distance <=
                        sc->sc_knobs.tap_track_distance_limit)) {
                        if (temporary_release) {
                                /*
                                 * XXX Kludge: Temporarily transition
                                 * to a tap state that uatp_input will
                                 * interpret as `no buttons tapped',
                                 * saving the tapping fingers.  There
                                 * should instead be a separate routine
                                 * uatp_input_untapped.
                                 */
                                unsigned int fingers = sc->sc_tapping_fingers;
                                tap_transition_initial(sc);
                                uatp_input(sc, 0, 0, 0, 0, 0);
                                sc->sc_tapping_fingers = fingers;
                        }
                        tap_transition_tapped(sc, &now);
                } else {
                        (*non_tapped_transition)(sc);
                }
                ok = true;
                break;

        case TAP_STATE_DRAGGING_DOWN:
                tap_transition_dragging_up(sc);
                ok = true;
                break;

        default:
                aprint_error_dev(uatp_dev(sc), "%s: invalid tap state: %d\n",
                    __func__, sc->sc_tap_state);
                tap_transition_initial(sc);
                ok = false;
                break;
        }
        TAP_DEBUG_POST(sc);
        mutex_exit(&sc->sc_tap_mutex);
        return ok;
}

/* Untapping: Releasing the button after a tap */

static void
schedule_untap(struct uatp_softc *sc)
{
        unsigned int ms = sc->sc_knobs.double_tap_limit_msec;
        if (ms <= 1000)
                callout_schedule(&sc->sc_untap_callout, mstohz(ms));
        else                    /* XXX Reject bogus values in sysctl.  */
                aprint_error_dev(uatp_dev(sc),
                    "double-tap delay too long: %ums\n", ms);
}

static void
untap_callout(void *arg)
{
        struct uatp_softc *sc = arg;

        mutex_enter(&sc->sc_tap_mutex);
        TAP_DEBUG_PRE(sc);
        switch (sc->sc_tap_state) {
        case TAP_STATE_TAPPED:
                tap_transition_initial(sc);
                /*
                 * XXX Kludge: Call uatp_input after the state transition
                 * to make sure that it will actually release the button.
                 */
                uatp_input(sc, 0, 0, 0, 0, 0);

        case TAP_STATE_INITIAL:
        case TAP_STATE_TAPPING:
        case TAP_STATE_DOUBLE_TAPPING:
        case TAP_STATE_DRAGGING_UP:
        case TAP_STATE_DRAGGING_DOWN:
        case TAP_STATE_TAPPING_IN_DRAG:
                /*
                 * Somebody else got in and changed the state before we
                 * untapped.  Let them take over; do nothing here.
                 */
                break;

        default:
                aprint_error_dev(uatp_dev(sc), "%s: invalid tap state: %d\n",
                    __func__, sc->sc_tap_state);
                tap_transition_initial(sc);
                /* XXX Just in case...?  */
                uatp_input(sc, 0, 0, 0, 0, 0);
                break;
        }
        TAP_DEBUG_POST(sc);
        mutex_exit(&sc->sc_tap_mutex);
}

/*
 * Emulate different buttons if the user holds down n fingers while
 * pressing the physical button.  (This is unrelated to tapping.)
 */

static uint32_t
emulated_buttons(struct uatp_softc *sc, unsigned int fingers)
{
        CHECK((1 < fingers), return 0);

        switch (fingers) {
        case 2:
                DPRINTF(sc, UATP_DEBUG_EMUL_BUTTON,
                    ("2-finger emulated button: %"PRIx32"\n",
                        sc->sc_knobs.two_finger_buttons));
                return sc->sc_knobs.two_finger_buttons;

        case 3:
        default:
                DPRINTF(sc, UATP_DEBUG_EMUL_BUTTON,
                    ("3-finger emulated button: %"PRIx32"\n",
                        sc->sc_knobs.three_finger_buttons));
                return sc->sc_knobs.three_finger_buttons;
        }
}

/*
 * Update the position known to the driver based on the position and
 * number of fingers.  dx, dy, dz, and dw are expected to hold zero;
 * update_position may store nonzero changes in position in them.
 */

static void
update_position(struct uatp_softc *sc, unsigned int fingers,
    unsigned int x_raw, unsigned int y_raw,
    int *dx, int *dy, int *dz, int *dw)
{
        CHECK((0 < fingers), return);

        if ((fingers == 1) || (sc->sc_knobs.multifinger_track == 1))
                move_mouse(sc, x_raw, y_raw, dx, dy);
        else if (sc->sc_knobs.multifinger_track == 2)
                scroll_wheel(sc, x_raw, y_raw, dz, dw);
}

/*
 * XXX Scrolling needs to use a totally different motion model.
 */

static void
move_mouse(struct uatp_softc *sc, unsigned int x_raw, unsigned int y_raw,
    int *dx, int *dy)
{
        move(sc, "mouse", x_raw, y_raw, &sc->sc_x_raw, &sc->sc_y_raw,
            &sc->sc_x_smoothed, &sc->sc_y_smoothed,
            &sc->sc_x_remainder, &sc->sc_y_remainder,
            dx, dy);
}

static void
scroll_wheel(struct uatp_softc *sc, unsigned int x_raw, unsigned int y_raw,
    int *dz, int *dw)
{
        move(sc, "scroll", x_raw, y_raw, &sc->sc_z_raw, &sc->sc_w_raw,
            &sc->sc_z_smoothed, &sc->sc_w_smoothed,
            &sc->sc_z_remainder, &sc->sc_w_remainder,
            dz, dw);
}

static void
move(struct uatp_softc *sc, const char *ctx, unsigned int a, unsigned int b,
    int *a_raw, int *b_raw,
    int *a_smoothed, int *b_smoothed,
    unsigned int *a_remainder, unsigned int *b_remainder,
    int *da, int *db)
{
#define CHECK_(condition) CHECK(condition, return)

        int old_a_raw = *a_raw, old_a_smoothed = *a_smoothed;
        int old_b_raw = *b_raw, old_b_smoothed = *b_smoothed;
        unsigned int a_dist, b_dist, dist_squared;
        bool a_fast, b_fast;

        /*
         * Make sure the quadratics in motion_below_threshold and
         * tracking distance don't overflow int arithmetic.
         */
        __CTASSERT(0x12000000 == (2 * UATP_MAX_POSITION * UATP_MAX_POSITION));

        CHECK_(a <= UATP_MAX_POSITION);
        CHECK_(b <= UATP_MAX_POSITION);
        *a_raw = a;
        *b_raw = b;
        if ((old_a_raw < 0) || (old_b_raw < 0)) {
                DPRINTF(sc, UATP_DEBUG_MOVE,
                    ("initialize %s position (%d, %d) -> (%d, %d)\n", ctx,
                        old_a_raw, old_b_raw, a, b));
                return;
        }

        if ((old_a_smoothed < 0) || (old_b_smoothed < 0)) {
                /* XXX Does this make sense?  */
                old_a_smoothed = old_a_raw;
                old_b_smoothed = old_b_raw;
        }

        CHECK_(0 <= old_a_raw);
        CHECK_(0 <= old_b_raw);
        CHECK_(old_a_raw <= UATP_MAX_POSITION);
        CHECK_(old_b_raw <= UATP_MAX_POSITION);
        CHECK_(0 <= old_a_smoothed);
        CHECK_(0 <= old_b_smoothed);
        CHECK_(old_a_smoothed <= UATP_MAX_POSITION);
        CHECK_(old_b_smoothed <= UATP_MAX_POSITION);
        CHECK_(0 <= *a_raw);
        CHECK_(0 <= *b_raw);
        CHECK_(*a_raw <= UATP_MAX_POSITION);
        CHECK_(*b_raw <= UATP_MAX_POSITION);
        *a_smoothed = smooth(sc, old_a_raw, old_a_smoothed, *a_raw);
        *b_smoothed = smooth(sc, old_b_raw, old_b_smoothed, *b_raw);
        CHECK_(0 <= *a_smoothed);
        CHECK_(0 <= *b_smoothed);
        CHECK_(*a_smoothed <= UATP_MAX_POSITION);
        CHECK_(*b_smoothed <= UATP_MAX_POSITION);

        if (sc->sc_motion_timer < sc->sc_knobs.motion_delay) {
                DPRINTF(sc, UATP_DEBUG_MOVE, ("delay motion %u\n",
                        sc->sc_motion_timer));
                sc->sc_motion_timer += 1;
                return;
        }

        /* XXX Use raw distances or smoothed distances?  Acceleration?  */
        if (*a_smoothed < old_a_smoothed)
                a_dist = old_a_smoothed - *a_smoothed;
        else
                a_dist = *a_smoothed - old_a_smoothed;

        if (*b_smoothed < old_b_smoothed)
                b_dist = old_b_smoothed - *b_smoothed;
        else
                b_dist = *b_smoothed - old_b_smoothed;

        dist_squared = (a_dist * a_dist) + (b_dist * b_dist);
        if (dist_squared < ((2 * UATP_MAX_POSITION * UATP_MAX_POSITION)
                - sc->sc_track_distance))
                sc->sc_track_distance += dist_squared;
        else
                sc->sc_track_distance = (2 * UATP_MAX_POSITION *
                    UATP_MAX_POSITION);
        DPRINTF(sc, UATP_DEBUG_TRACK_DIST, ("finger has tracked %u units^2\n",
                sc->sc_track_distance));

        /*
         * The checks above guarantee that the differences here are at
         * most UATP_MAX_POSITION in magnitude, since both minuend and
         * subtrahend are nonnegative and at most UATP_MAX_POSITION.
         */
        if (motion_below_threshold(sc, sc->sc_knobs.motion_threshold,
                (int)(*a_smoothed - old_a_smoothed),
                (int)(*b_smoothed - old_b_smoothed))) {
                DPRINTF(sc, UATP_DEBUG_MOVE,
                    ("%s motion too small: (%d, %d) -> (%d, %d)\n", ctx,
                        old_a_smoothed, old_b_smoothed,
                        *a_smoothed, *b_smoothed));
                return;
        }
        if (sc->sc_knobs.fast_per_direction == 0) {
                a_fast = b_fast = !motion_below_threshold(sc,
                    sc->sc_knobs.fast_motion_threshold,
                    (int)(*a_smoothed - old_a_smoothed),
                    (int)(*b_smoothed - old_b_smoothed));
        } else {
                a_fast = !motion_below_threshold(sc,
                    sc->sc_knobs.fast_motion_threshold,
                    (int)(*a_smoothed - old_a_smoothed),
                    0);
                b_fast = !motion_below_threshold(sc,
                    sc->sc_knobs.fast_motion_threshold,
                    0,
                    (int)(*b_smoothed - old_b_smoothed));
        }
        *da = accelerate(sc, old_a_raw, *a_raw, old_a_smoothed, *a_smoothed,
            a_fast, a_remainder);
        *db = accelerate(sc, old_b_raw, *b_raw, old_b_smoothed, *b_smoothed,
            b_fast, b_remainder);
        DPRINTF(sc, UATP_DEBUG_MOVE,
            ("update %s position (%d, %d) -> (%d, %d), move by (%d, %d)\n",
                ctx, old_a_smoothed, old_b_smoothed, *a_smoothed, *b_smoothed,
                *da, *db));

#undef CHECK_
}

static int
smooth(struct uatp_softc *sc, unsigned int old_raw, unsigned int old_smoothed,
    unsigned int raw)
{
#define CHECK_(condition) CHECK(condition, return old_raw)

        /*
         * Arithmetic bounds:
         * . the weights are at most UATP_MAX_WEIGHT;
         * . the positions are at most UATP_MAX_POSITION; and so
         * . the numerator of the average is at most
         *     3 * UATP_MAX_WEIGHT * UATP_MAX_POSITION,
         *   which is #x477000, fitting comfortably in an int.
         */
        __CTASSERT(0x477000 == (3 * UATP_MAX_WEIGHT * UATP_MAX_POSITION));
        unsigned int old_raw_weight = uatp_old_raw_weight(sc);
        unsigned int old_smoothed_weight = uatp_old_smoothed_weight(sc);
        unsigned int new_raw_weight = uatp_new_raw_weight(sc);
        CHECK_(old_raw_weight <= UATP_MAX_WEIGHT);
        CHECK_(old_smoothed_weight <= UATP_MAX_WEIGHT);
        CHECK_(new_raw_weight <= UATP_MAX_WEIGHT);
        CHECK_(old_raw <= UATP_MAX_POSITION);
        CHECK_(old_smoothed <= UATP_MAX_POSITION);
        CHECK_(raw <= UATP_MAX_POSITION);
        return (((old_raw_weight * old_raw) +
                (old_smoothed_weight * old_smoothed) +
                (new_raw_weight * raw))
            / (old_raw_weight + old_smoothed_weight + new_raw_weight));

#undef CHECK_
}

static bool
motion_below_threshold(struct uatp_softc *sc, unsigned int threshold,
    int x, int y)
{
        unsigned int x_squared, y_squared;

        /* Caller guarantees the multiplication will not overflow.  */
        KASSERT(-UATP_MAX_POSITION <= x);
        KASSERT(-UATP_MAX_POSITION <= y);
        KASSERT(x <= UATP_MAX_POSITION);
        KASSERT(y <= UATP_MAX_POSITION);
        __CTASSERT(0x12000000 == (2 * UATP_MAX_POSITION * UATP_MAX_POSITION));

        x_squared = (x * x);
        y_squared = (y * y);

        return (x_squared + y_squared) < threshold;
}

static int
accelerate(struct uatp_softc *sc, unsigned int old_raw, unsigned int raw,
    unsigned int old_smoothed, unsigned int smoothed, bool fast,
    int *remainder)
{
#define CHECK_(condition) CHECK(condition, return 0)

        /* Guarantee that the scaling won't overflow.  */
        __CTASSERT(0x30000 ==
            (UATP_MAX_POSITION * UATP_MAX_MOTION_MULTIPLIER));

        CHECK_(old_raw <= UATP_MAX_POSITION);
        CHECK_(raw <= UATP_MAX_POSITION);
        CHECK_(old_smoothed <= UATP_MAX_POSITION);
        CHECK_(smoothed <= UATP_MAX_POSITION);

        return (fast ? uatp_scale_fast_motion : uatp_scale_motion)
            (sc, (((int) smoothed) - ((int) old_smoothed)), remainder);

#undef CHECK_
}

MODULE(MODULE_CLASS_DRIVER, uatp, NULL);

#ifdef _MODULE
#include "ioconf.c"
#endif

static int
uatp_modcmd(modcmd_t cmd, void *aux)
{
        int error = 0;

        switch (cmd) {
        case MODULE_CMD_INIT:
#ifdef _MODULE
                error = config_init_component(cfdriver_ioconf_uatp,
                    cfattach_ioconf_uatp, cfdata_ioconf_uatp);
#endif
                return error;
        case MODULE_CMD_FINI:
#ifdef _MODULE
                error = config_fini_component(cfdriver_ioconf_uatp,
                    cfattach_ioconf_uatp, cfdata_ioconf_uatp);
#endif
                return error;
        default:
                return ENOTTY;
        }
}