Input: add driver for Hynitron CST816x series

Introduce support for the Hynitron CST816x series touchscreen controller
used for 240×240 1.28-inch Round LCD Display Module manufactured
by Waveshare Electronics. The driver is designed based on an Arduino
implementation marked as under MIT License. This driver is written
for a particular round display based on the CST816S controller, which
is not compatiable with existing driver for Hynitron controllers.

Signed-off-by: Oleh Kuzhylnyi <kuzhylol@gmail.com>
Link: https://lore.kernel.org/r/20250921125939.249788-2-kuzhylol@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Author: kuzhylol

drivers/input/touchscreen/Kconfig

@@ -475,6 +475,18 @@ config TOUCHSCREEN_HYNITRON_CSTXXX
 	  To compile this driver as a module, choose M here: the
 	  module will be called hynitron-cstxxx.
 
+config TOUCHSCREEN_HYNITRON_CST816X
+	tristate "Hynitron CST816x touchscreen"
+	depends on I2C
+	help
+	  Say Y here if you have a touchscreen using a Hynitron
+	  CST816x series touchscreen controller.
+
+	  If unsure, say N.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called hynitron-cst816x.
+
 config TOUCHSCREEN_ILI210X
 	tristate "Ilitek ILI210X based touchscreen"
 	depends on I2C

drivers/input/touchscreen/Makefile

@@ -51,6 +51,7 @@ obj-$(CONFIG_TOUCHSCREEN_GOODIX_BERLIN_SPI)	+= goodix_berlin_spi.o
 obj-$(CONFIG_TOUCHSCREEN_HIDEEP)	+= hideep.o
 obj-$(CONFIG_TOUCHSCREEN_HIMAX_HX852X)	+= himax_hx852x.o
 obj-$(CONFIG_TOUCHSCREEN_HYNITRON_CSTXXX)	+= hynitron_cstxxx.o
+obj-$(CONFIG_TOUCHSCREEN_HYNITRON_CST816X)	+= hynitron-cst816x.o
 obj-$(CONFIG_TOUCHSCREEN_ILI210X)	+= ili210x.o
 obj-$(CONFIG_TOUCHSCREEN_ILITEK)	+= ilitek_ts_i2c.o
 obj-$(CONFIG_TOUCHSCREEN_IMAGIS)	+= imagis.o

drivers/input/touchscreen/hynitron-cst816x.c

@@ -0,0 +1,253 @@
+// 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");