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// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Driver for I2C connected Hynitron CST816x Series Touchscreen
 *
 * Copyright (C) 2025 Oleh Kuzhylnyi <kuzhylol@gmail.com>
 */

#include <linux/delay.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/gpio/consumer.h>
#include <linux/i2c.h>
#include <linux/input.h>
#include <linux/unaligned.h>
#include <linux/interrupt.h>
#include <linux/module.h>

#define CST816X_RD_REG		0x01
#define CST816X_NUM_KEYS	5

struct cst816x_touch {
	u8 gest;
	u8 active;
	u16 abs_x;
	u16 abs_y;
} __packed;

struct cst816x_priv {
	struct i2c_client *client;
	struct gpio_desc *reset;
	struct input_dev *input;
	unsigned int keycode[CST816X_NUM_KEYS];
	unsigned int keycodemax;
};

static int cst816x_parse_keycodes(struct device *dev, struct cst816x_priv *priv)
{
	int count;
	int error;

	if (device_property_present(dev, "linux,keycodes")) {
		count = device_property_count_u32(dev, "linux,keycodes");
		if (count < 0) {
			error = count;
			dev_err(dev, "failed to count keys: %d\n", error);
			return error;
		} else if (count > ARRAY_SIZE(priv->keycode)) {
			dev_err(dev, "too many keys defined: %d\n", count);
			return -EINVAL;
		}
		priv->keycodemax = count;

		error = device_property_read_u32_array(dev, "linux,keycodes",
						       priv->keycode,
						       priv->keycodemax);
		if (error) {
			dev_err(dev, "failed to read keycodes: %d\n", error);
			return error;
		}
	}

	return 0;
}

static int cst816x_i2c_read_register(struct cst816x_priv *priv, u8 reg,
				     void *buf, size_t len)
{
	struct i2c_msg xfer[] = {
		{
			.addr = priv->client->addr,
			.flags = 0,
			.buf = &reg,
			.len = sizeof(reg),
		},
		{
			.addr = priv->client->addr,
			.flags = I2C_M_RD,
			.buf = buf,
			.len = len,
		},
	};
	int error;
	int ret;

	ret = i2c_transfer(priv->client->adapter, xfer, ARRAY_SIZE(xfer));
	if (ret != ARRAY_SIZE(xfer)) {
		error = ret < 0 ? ret : -EIO;
		dev_err(&priv->client->dev, "i2c rx err: %d\n", error);
		return error;
	}

	return 0;
}

static u8 cst816x_gest_idx(u8 gest)
{
	u8 index;

	switch (gest) {
	case 0x01: /* Slide up gesture */
	case 0x02: /* Slide down gesture */
	case 0x03: /* Slide left gesture */
	case 0x04: /* Slide right gesture */
		index = gest;
		break;
	case 0x0c: /* Long press gesture */
	default:
		index = CST816X_NUM_KEYS;
		break;
	}

	return index - 1;
}

static bool cst816x_process_touch(struct cst816x_priv *priv,
				  struct cst816x_touch *tch)
{
	if (cst816x_i2c_read_register(priv, CST816X_RD_REG, tch, sizeof(*tch)))
		return false;

	tch->abs_x = get_unaligned_be16(&tch->abs_x) & GENMASK(11, 0);
	tch->abs_y = get_unaligned_be16(&tch->abs_y) & GENMASK(11, 0);

	dev_dbg(&priv->client->dev, "x: %u, y: %u, t: %u, g: 0x%x\n",
		tch->abs_x, tch->abs_y, tch->active, tch->gest);

	return true;
}

static int cst816x_register_input(struct cst816x_priv *priv)
{
	priv->input = devm_input_allocate_device(&priv->client->dev);
	if (!priv->input)
		return -ENOMEM;

	priv->input->name = "Hynitron CST816x Series Touchscreen";
	priv->input->phys = "input/ts";
	priv->input->id.bustype = BUS_I2C;

	input_set_drvdata(priv->input, priv);

	input_set_abs_params(priv->input, ABS_X, 0, 240, 0, 0);
	input_set_abs_params(priv->input, ABS_Y, 0, 240, 0, 0);
	input_set_capability(priv->input, EV_KEY, BTN_TOUCH);

	priv->input->keycode = priv->keycode;
	priv->input->keycodesize = sizeof(priv->keycode[0]);
	priv->input->keycodemax = priv->keycodemax;

	for (int i = 0; i < priv->keycodemax; i++) {
		if (priv->keycode[i] == KEY_RESERVED)
			continue;

		input_set_capability(priv->input, EV_KEY, priv->keycode[i]);
	}

	return input_register_device(priv->input);
}

static void cst816x_reset(struct cst816x_priv *priv)
{
	gpiod_set_value_cansleep(priv->reset, 1);
	msleep(50);
	gpiod_set_value_cansleep(priv->reset, 0);
	msleep(100);
}

static irqreturn_t cst816x_irq_cb(int irq, void *cookie)
{
	struct cst816x_priv *priv = cookie;
	struct cst816x_touch tch;

	if (!cst816x_process_touch(priv, &tch))
		return IRQ_HANDLED;

	input_report_abs(priv->input, ABS_X, tch.abs_x);
	input_report_abs(priv->input, ABS_Y, tch.abs_y);

	if (tch.gest)
		input_report_key(priv->input,
				 priv->keycode[cst816x_gest_idx(tch.gest)],
				 tch.active);

	input_report_key(priv->input, BTN_TOUCH, tch.active);

	input_sync(priv->input);

	return IRQ_HANDLED;
}

static int cst816x_probe(struct i2c_client *client)
{
	struct device *dev = &client->dev;
	struct cst816x_priv *priv;
	int error;

	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
	if (!priv)
		return -ENOMEM;

	priv->client = client;

	priv->reset = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
	if (IS_ERR(priv->reset))
		return dev_err_probe(dev, PTR_ERR(priv->reset),
				     "gpio reset request failed\n");

	if (priv->reset)
		cst816x_reset(priv);

	error = cst816x_parse_keycodes(dev, priv);
	if (error)
		dev_warn(dev, "no gestures found in dt\n");

	error = cst816x_register_input(priv);
	if (error)
		return dev_err_probe(dev, error, "input register failed\n");

	error = devm_request_threaded_irq(dev, client->irq,
					  NULL, cst816x_irq_cb, IRQF_ONESHOT,
					  dev_driver_string(dev), priv);
	if (error)
		return dev_err_probe(dev, error, "irq request failed\n");

	return 0;
}

static const struct i2c_device_id cst816x_id[] = {
	{ .name = "cst816s", 0 },
	{ }
};
MODULE_DEVICE_TABLE(i2c, cst816x_id);

static const struct of_device_id cst816x_of_match[] = {
	{ .compatible = "hynitron,cst816s", },
	{ }
};
MODULE_DEVICE_TABLE(of, cst816x_of_match);

static struct i2c_driver cst816x_driver = {
	.driver = {
		.name = "cst816x",
		.of_match_table = cst816x_of_match,
	},
	.id_table = cst816x_id,
	.probe = cst816x_probe,
};

module_i2c_driver(cst816x_driver);

MODULE_AUTHOR("Oleh Kuzhylnyi <kuzhylol@gmail.com>");
MODULE_DESCRIPTION("Hynitron CST816x Series Touchscreen Driver");
MODULE_LICENSE("GPL");