// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  Copyright (c) 2001 Arndt Schoenewald
 *  Copyright (c) 2000-2001 Vojtech Pavlik
 *  Copyright (c) 2000 Mark Fletcher
 *
 *  Sponsored by Quelltext AG (http://www.quelltext-ag.de), Dortmund, Germany
 */

/*
 * Driver to use Handykey's Twiddler (the first edition, i.e. the one with
 * the RS232 interface) as a joystick under Linux
 *
 * The Twiddler is a one-handed chording keyboard featuring twelve buttons on
 * the front, six buttons on the top, and a built-in tilt sensor. The buttons
 * on the front, which are grouped as four rows of three buttons, are pressed
 * by the four fingers (this implies only one button per row can be held down
 * at the same time) and the buttons on the top are for the thumb. The tilt
 * sensor delivers X and Y axis data depending on how the Twiddler is held.
 * Additional information can be found at http://www.handykey.com.
 *
 * This driver does not use the Twiddler for its intended purpose, i.e. as
 * a chording keyboard, but as a joystick: pressing and releasing a button
 * immediately sends a corresponding button event, and tilting it generates
 * corresponding ABS_X and ABS_Y events. This turns the Twiddler into a game
 * controller with amazing 18 buttons :-)
 *
 * Note: The Twiddler2 (the successor of the Twiddler that connects directly
 * to the PS/2 keyboard and mouse ports) is NOT supported by this driver!
 *
 * For questions or feedback regarding this driver module please contact:
 * Arndt Schoenewald <arndt@quelltext.com>
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/input.h>
#include <linux/serio.h>

#define DRIVER_DESC     "Handykey Twiddler keyboard as a joystick driver"

MODULE_DESCRIPTION(DRIVER_DESC);
MODULE_LICENSE("GPL");

/*
 * Constants.
 */

#define TWIDJOY_MAX_LENGTH 5

static struct twidjoy_button_spec {
        int bitshift;
        int bitmask;
        int buttons[3];
}
twidjoy_buttons[] = {
        {  0, 3, { BTN_A,      BTN_B,     BTN_C    } },
        {  2, 3, { BTN_X,      BTN_Y,     BTN_Z    } },
        {  4, 3, { BTN_TL,     BTN_TR,    BTN_TR2  } },
        {  6, 3, { BTN_SELECT, BTN_START, BTN_MODE } },
        {  8, 1, { BTN_BASE5                       } },
        {  9, 1, { BTN_BASE                        } },
        { 10, 1, { BTN_BASE3                       } },
        { 11, 1, { BTN_BASE4                       } },
        { 12, 1, { BTN_BASE2                       } },
        { 13, 1, { BTN_BASE6                       } },
        { 0,  0, { 0                               } }
};

/*
 * Per-Twiddler data.
 */

struct twidjoy {
        struct input_dev *dev;
        int idx;
        unsigned char data[TWIDJOY_MAX_LENGTH];
        char phys[32];
};

/*
 * twidjoy_process_packet() decodes packets the driver receives from the
 * Twiddler. It updates the data accordingly.
 */

static void twidjoy_process_packet(struct twidjoy *twidjoy)
{
        struct input_dev *dev = twidjoy->dev;
        unsigned char *data = twidjoy->data;
        struct twidjoy_button_spec *bp;
        int button_bits, abs_x, abs_y;

        button_bits = ((data[1] & 0x7f) << 7) | (data[0] & 0x7f);

        for (bp = twidjoy_buttons; bp->bitmask; bp++) {
                int value = (button_bits & (bp->bitmask << bp->bitshift)) >> bp->bitshift;
                int i;

                for (i = 0; i < bp->bitmask; i++)
                        input_report_key(dev, bp->buttons[i], i+1 == value);
        }

        abs_x = ((data[4] & 0x07) << 5) | ((data[3] & 0x7C) >> 2);
        if (data[4] & 0x08) abs_x -= 256;

        abs_y = ((data[3] & 0x01) << 7) | ((data[2] & 0x7F) >> 0);
        if (data[3] & 0x02) abs_y -= 256;

        input_report_abs(dev, ABS_X, -abs_x);
        input_report_abs(dev, ABS_Y, +abs_y);

        input_sync(dev);
}

/*
 * twidjoy_interrupt() is called by the low level driver when characters
 * are ready for us. We then buffer them for further processing, or call the
 * packet processing routine.
 */

static irqreturn_t twidjoy_interrupt(struct serio *serio, unsigned char data, unsigned int flags)
{
        struct twidjoy *twidjoy = serio_get_drvdata(serio);

        /* All Twiddler packets are 5 bytes. The fact that the first byte
         * has a MSB of 0 and all other bytes have a MSB of 1 can be used
         * to check and regain sync. */

        if ((data & 0x80) == 0)
                twidjoy->idx = 0;       /* this byte starts a new packet */
        else if (twidjoy->idx == 0)
                return IRQ_HANDLED;     /* wrong MSB -- ignore this byte */

        if (twidjoy->idx < TWIDJOY_MAX_LENGTH)
                twidjoy->data[twidjoy->idx++] = data;

        if (twidjoy->idx == TWIDJOY_MAX_LENGTH) {
                twidjoy_process_packet(twidjoy);
                twidjoy->idx = 0;
        }

        return IRQ_HANDLED;
}

/*
 * twidjoy_disconnect() is the opposite of twidjoy_connect()
 */

static void twidjoy_disconnect(struct serio *serio)
{
        struct twidjoy *twidjoy = serio_get_drvdata(serio);

        serio_close(serio);
        serio_set_drvdata(serio, NULL);
        input_unregister_device(twidjoy->dev);
        kfree(twidjoy);
}

/*
 * twidjoy_connect() is the routine that is called when someone adds a
 * new serio device. It looks for the Twiddler, and if found, registers
 * it as an input device.
 */

static int twidjoy_connect(struct serio *serio, struct serio_driver *drv)
{
        struct twidjoy_button_spec *bp;
        struct twidjoy *twidjoy;
        struct input_dev *input_dev;
        int err = -ENOMEM;
        int i;

        twidjoy = kzalloc_obj(*twidjoy);
        input_dev = input_allocate_device();
        if (!twidjoy || !input_dev)
                goto fail1;

        twidjoy->dev = input_dev;
        snprintf(twidjoy->phys, sizeof(twidjoy->phys), "%s/input0", serio->phys);

        input_dev->name = "Handykey Twiddler";
        input_dev->phys = twidjoy->phys;
        input_dev->id.bustype = BUS_RS232;
        input_dev->id.vendor = SERIO_TWIDJOY;
        input_dev->id.product = 0x0001;
        input_dev->id.version = 0x0100;
        input_dev->dev.parent = &serio->dev;

        input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
        input_set_abs_params(input_dev, ABS_X, -50, 50, 4, 4);
        input_set_abs_params(input_dev, ABS_Y, -50, 50, 4, 4);

        for (bp = twidjoy_buttons; bp->bitmask; bp++)
                for (i = 0; i < bp->bitmask; i++)
                        set_bit(bp->buttons[i], input_dev->keybit);

        serio_set_drvdata(serio, twidjoy);

        err = serio_open(serio, drv);
        if (err)
                goto fail2;

        err = input_register_device(twidjoy->dev);
        if (err)
                goto fail3;

        return 0;

 fail3: serio_close(serio);
 fail2: serio_set_drvdata(serio, NULL);
 fail1: input_free_device(input_dev);
        kfree(twidjoy);
        return err;
}

/*
 * The serio driver structure.
 */

static const struct serio_device_id twidjoy_serio_ids[] = {
        {
                .type   = SERIO_RS232,
                .proto  = SERIO_TWIDJOY,
                .id     = SERIO_ANY,
                .extra  = SERIO_ANY,
        },
        { 0 }
};

MODULE_DEVICE_TABLE(serio, twidjoy_serio_ids);

static struct serio_driver twidjoy_drv = {
        .driver         = {
                .name   = "twidjoy",
        },
        .description    = DRIVER_DESC,
        .id_table       = twidjoy_serio_ids,
        .interrupt      = twidjoy_interrupt,
        .connect        = twidjoy_connect,
        .disconnect     = twidjoy_disconnect,
};

module_serio_driver(twidjoy_drv);