// SPDX-License-Identifier: GPL-2.0
/*
 * FS-iA6B iBus RC receiver driver
 *
 * This driver provides all 14 channels of the FlySky FS-ia6B RC receiver
 * as analog values.
 *
 * Additionally, the channels can be converted to discrete switch values.
 * By default, it is configured for the offical FS-i6 remote control.
 * If you use a different hardware configuration, you can configure it
 * using the `switch_config` parameter.
 */

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

#define DRIVER_DESC             "FS-iA6B iBus RC receiver"

MODULE_AUTHOR("Markus Koch <markus@notsyncing.net>");
MODULE_DESCRIPTION(DRIVER_DESC);
MODULE_LICENSE("GPL");

#define IBUS_SERVO_COUNT        14

static char *switch_config = "00000022320000";
module_param(switch_config, charp, 0444);
MODULE_PARM_DESC(switch_config,
                 "Amount of switch positions per channel (14 characters, 0-3)");

static int fsia6b_axes[IBUS_SERVO_COUNT] = {
        ABS_X, ABS_Y,
        ABS_Z, ABS_RX,
        ABS_RY, ABS_RZ,
        ABS_HAT0X, ABS_HAT0Y,
        ABS_HAT1X, ABS_HAT1Y,
        ABS_HAT2X, ABS_HAT2Y,
        ABS_HAT3X, ABS_HAT3Y
};

enum ibus_state { SYNC, COLLECT, PROCESS };

struct ibus_packet {
        enum ibus_state state;

        int offset;
        u16 ibuf;
        u16 channel[IBUS_SERVO_COUNT];
};

struct fsia6b {
        struct input_dev *dev;
        struct ibus_packet packet;

        char phys[32];
};

static irqreturn_t fsia6b_serio_irq(struct serio *serio,
                                    unsigned char data, unsigned int flags)
{
        struct fsia6b *fsia6b = serio_get_drvdata(serio);
        int i;
        int sw_state;
        int sw_id = BTN_0;

        fsia6b->packet.ibuf = (data << 8) | ((fsia6b->packet.ibuf >> 8) & 0xFF);

        switch (fsia6b->packet.state) {
        case SYNC:
                if (fsia6b->packet.ibuf == 0x4020)
                        fsia6b->packet.state = COLLECT;
                break;

        case COLLECT:
                fsia6b->packet.state = PROCESS;
                break;

        case PROCESS:
                fsia6b->packet.channel[fsia6b->packet.offset] =
                                fsia6b->packet.ibuf;
                fsia6b->packet.offset++;

                if (fsia6b->packet.offset == IBUS_SERVO_COUNT) {
                        fsia6b->packet.offset = 0;
                        fsia6b->packet.state = SYNC;
                        for (i = 0; i < IBUS_SERVO_COUNT; ++i) {
                                input_report_abs(fsia6b->dev, fsia6b_axes[i],
                                                 fsia6b->packet.channel[i]);

                                sw_state = 0;
                                if (fsia6b->packet.channel[i] > 1900)
                                        sw_state = 1;
                                else if (fsia6b->packet.channel[i] < 1100)
                                        sw_state = 2;

                                switch (switch_config[i]) {
                                case '3':
                                        input_report_key(fsia6b->dev,
                                                         sw_id++,
                                                         sw_state == 0);
                                        fallthrough;
                                case '2':
                                        input_report_key(fsia6b->dev,
                                                         sw_id++,
                                                         sw_state == 1);
                                        fallthrough;
                                case '1':
                                        input_report_key(fsia6b->dev,
                                                         sw_id++,
                                                         sw_state == 2);
                                }
                        }
                        input_sync(fsia6b->dev);
                } else {
                        fsia6b->packet.state = COLLECT;
                }
                break;
        }

        return IRQ_HANDLED;
}

static int fsia6b_serio_connect(struct serio *serio, struct serio_driver *drv)
{
        struct fsia6b *fsia6b;
        struct input_dev *input_dev;
        int err;
        int i, j;
        int sw_id = 0;

        fsia6b = kzalloc_obj(*fsia6b);
        if (!fsia6b)
                return -ENOMEM;

        fsia6b->packet.ibuf = 0;
        fsia6b->packet.offset = 0;
        fsia6b->packet.state = SYNC;

        serio_set_drvdata(serio, fsia6b);

        input_dev = input_allocate_device();
        if (!input_dev) {
                err = -ENOMEM;
                goto fail1;
        }
        fsia6b->dev = input_dev;

        scnprintf(fsia6b->phys, sizeof(fsia6b->phys), "%s/input0", serio->phys);

        input_dev->name = DRIVER_DESC;
        input_dev->phys = fsia6b->phys;
        input_dev->id.bustype = BUS_RS232;
        input_dev->id.vendor = SERIO_FSIA6B;
        input_dev->id.product = serio->id.id;
        input_dev->id.version = 0x0100;
        input_dev->dev.parent = &serio->dev;

        for (i = 0; i < IBUS_SERVO_COUNT; i++)
                input_set_abs_params(input_dev, fsia6b_axes[i],
                                     1000, 2000, 2, 2);

        /* Register switch configuration */
        for (i = 0; i < IBUS_SERVO_COUNT; i++) {
                if (switch_config[i] < '0' || switch_config[i] > '3') {
                        dev_err(&fsia6b->dev->dev,
                                "Invalid switch configuration supplied for fsia6b.\n");
                        err = -EINVAL;
                        goto fail2;
                }

                for (j = '1'; j <= switch_config[i]; j++) {
                        input_set_capability(input_dev, EV_KEY, BTN_0 + sw_id);
                        sw_id++;
                }
        }

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

        err = input_register_device(fsia6b->dev);
        if (err)
                goto fail3;

        return 0;

fail3:  serio_close(serio);
fail2:  input_free_device(input_dev);
fail1:  serio_set_drvdata(serio, NULL);
        kfree(fsia6b);
        return err;
}

static void fsia6b_serio_disconnect(struct serio *serio)
{
        struct fsia6b *fsia6b = serio_get_drvdata(serio);

        serio_close(serio);
        serio_set_drvdata(serio, NULL);
        input_unregister_device(fsia6b->dev);
        kfree(fsia6b);
}

static const struct serio_device_id fsia6b_serio_ids[] = {
        {
                .type   = SERIO_RS232,
                .proto  = SERIO_FSIA6B,
                .id     = SERIO_ANY,
                .extra  = SERIO_ANY,
        },
        { 0 }
};

MODULE_DEVICE_TABLE(serio, fsia6b_serio_ids);

static struct serio_driver fsia6b_serio_drv = {
        .driver         = {
                .name   = "fsia6b"
        },
        .description    = DRIVER_DESC,
        .id_table       = fsia6b_serio_ids,
        .interrupt      = fsia6b_serio_irq,
        .connect        = fsia6b_serio_connect,
        .disconnect     = fsia6b_serio_disconnect
};

module_serio_driver(fsia6b_serio_drv)