gpio: add GPIO controller found on Waveshare DSI TOUCH panels

The Waveshare DSI TOUCH family of panels has separate on-board GPIO
controller, which controls power supplies to the panel and the touch
screen and provides reset pins for both the panel and the touchscreen.
Also it provides a simple PWM controller for panel backlight. Add
support for this GPIO controller.

Tested-by: Riccardo Mereu <r.mereu@arduino.cc>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Link: https://patch.msgid.link/20260507-waveshare-dsi-touch-v5-2-d2ac7ccc22d4@oss.qualcomm.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>

drivers/gpio/Kconfig

@@ -806,6 +806,16 @@ config GPIO_VISCONTI
 	help
 	  Say yes here to support GPIO on Tohisba Visconti.
 
+config GPIO_WAVESHARE_DSI_TOUCH
+	tristate "Waveshare GPIO controller for DSI panels"
+	depends on BACKLIGHT_CLASS_DEVICE
+	depends on I2C
+	select REGMAP_I2C
+	help
+	  Enable support for the GPIO and PWM controller found on Waveshare DSI
+	  TOUCH panel kits. It provides GPIOs (used for regulator control and
+          resets) and backlight support.
+
 config GPIO_WCD934X
 	tristate "Qualcomm WCD9340/WCD9341 GPIO controller driver"
 	depends on MFD_WCD934X

drivers/gpio/Makefile

@@ -205,6 +205,7 @@ obj-$(CONFIG_GPIO_VIRTUSER)		+= gpio-virtuser.o
 obj-$(CONFIG_GPIO_VIRTIO)		+= gpio-virtio.o
 obj-$(CONFIG_GPIO_VISCONTI)		+= gpio-visconti.o
 obj-$(CONFIG_GPIO_VX855)		+= gpio-vx855.o
+obj-$(CONFIG_GPIO_WAVESHARE_DSI_TOUCH)	+= gpio-waveshare-dsi.o
 obj-$(CONFIG_GPIO_WCD934X)		+= gpio-wcd934x.o
 obj-$(CONFIG_GPIO_WHISKEY_COVE)		+= gpio-wcove.o
 obj-$(CONFIG_GPIO_WINBOND)		+= gpio-winbond.o

drivers/gpio/gpio-waveshare-dsi.c

@@ -0,0 +1,208 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2024 Waveshare International Limited
+ * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
+ */
+
+#include <linux/backlight.h>
+#include <linux/err.h>
+#include <linux/fb.h>
+#include <linux/gpio/driver.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/regmap.h>
+
+/* I2C registers of the microcontroller. */
+#define REG_TP		0x94
+#define REG_LCD		0x95
+#define REG_PWM		0x96
+#define REG_SIZE	0x97
+#define REG_ID		0x98
+#define REG_VERSION	0x99
+
+enum {
+	GPIO_AVDD = 0,
+	GPIO_PANEL_RESET = 1,
+	GPIO_BL_ENABLE = 2,
+	GPIO_IOVCC = 4,
+	GPIO_VCC = 8,
+	GPIO_TS_RESET = 9,
+};
+
+#define NUM_GPIO 16
+
+struct waveshare_gpio {
+	struct mutex dir_lock;
+	struct mutex pwr_lock;
+	struct regmap *regmap;
+	u16 poweron_state;
+
+	struct gpio_chip gc;
+};
+
+static const struct regmap_config waveshare_gpio_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = REG_VERSION,
+};
+
+static int waveshare_gpio_get(struct waveshare_gpio *state, unsigned int offset)
+{
+	u16 pwr_state;
+
+	guard(mutex)(&state->pwr_lock);
+	pwr_state = state->poweron_state & BIT(offset);
+
+	return !!pwr_state;
+}
+
+static int waveshare_gpio_set(struct waveshare_gpio *state, unsigned int offset, int value)
+{
+	u16 last_val;
+	int err;
+
+	guard(mutex)(&state->pwr_lock);
+
+	last_val = state->poweron_state;
+	if (value)
+		last_val |= BIT(offset);
+	else
+		last_val &= ~BIT(offset);
+
+	state->poweron_state = last_val;
+
+	err = regmap_write(state->regmap, REG_TP, last_val >> 8);
+	if (!err)
+		err = regmap_write(state->regmap, REG_LCD, last_val & 0xff);
+
+	return err;
+}
+
+static int waveshare_gpio_gpio_get_direction(struct gpio_chip *gc, unsigned int offset)
+{
+	return GPIO_LINE_DIRECTION_OUT;
+}
+
+static int waveshare_gpio_gpio_get(struct gpio_chip *gc, unsigned int offset)
+{
+	struct waveshare_gpio *state = gpiochip_get_data(gc);
+
+	return waveshare_gpio_get(state, offset);
+}
+
+static int waveshare_gpio_gpio_set(struct gpio_chip *gc, unsigned int offset, int value)
+{
+	struct waveshare_gpio *state = gpiochip_get_data(gc);
+
+	return waveshare_gpio_set(state, offset, value);
+}
+
+static int waveshare_gpio_update_status(struct backlight_device *bl)
+{
+	struct waveshare_gpio *state = bl_get_data(bl);
+	int brightness = backlight_get_brightness(bl);
+
+	waveshare_gpio_set(state, GPIO_BL_ENABLE, brightness);
+
+	return regmap_write(state->regmap, REG_PWM, brightness);
+}
+
+static const struct backlight_ops waveshare_gpio_bl = {
+	.update_status = waveshare_gpio_update_status,
+};
+
+static int waveshare_gpio_probe(struct i2c_client *i2c)
+{
+	struct backlight_properties props = {};
+	struct waveshare_gpio *state;
+	struct device *dev = &i2c->dev;
+	struct backlight_device *bl;
+	struct regmap *regmap;
+	unsigned int data;
+	int ret;
+
+	state = devm_kzalloc(dev, sizeof(*state), GFP_KERNEL);
+	if (!state)
+		return -ENOMEM;
+
+	ret = devm_mutex_init(dev, &state->dir_lock);
+	if (ret)
+		return ret;
+
+	ret = devm_mutex_init(dev, &state->pwr_lock);
+	if (ret)
+		return ret;
+
+	regmap = devm_regmap_init_i2c(i2c, &waveshare_gpio_regmap_config);
+	if (IS_ERR(regmap))
+		return dev_err_probe(dev, PTR_ERR(regmap), "Failed to allocate register map\n");
+
+	state->regmap = regmap;
+	i2c_set_clientdata(i2c, state);
+
+	ret = regmap_read(regmap, REG_ID, &data);
+	if (ret < 0)
+		return dev_err_probe(dev, ret, "Failed to read register\n");
+
+	dev_dbg(dev, "waveshare panel hw id = 0x%x\n", data);
+
+	ret = regmap_read(regmap, REG_SIZE, &data);
+	if (ret < 0)
+		return dev_err_probe(dev, ret, "Failed to read register\n");
+
+	dev_dbg(dev, "waveshare panel size = %d\n", data);
+
+	ret = regmap_read(regmap, REG_VERSION, &data);
+	if (ret < 0)
+		return dev_err_probe(dev, ret, "Failed to read register\n");
+
+	dev_dbg(dev, "waveshare panel mcu version = 0x%x\n", data);
+
+	ret = waveshare_gpio_set(state, GPIO_TS_RESET, 1);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to program GPIOs\n");
+
+	msleep(20);
+
+	state->gc.parent = dev;
+	state->gc.label = i2c->name;
+	state->gc.owner = THIS_MODULE;
+	state->gc.base = -1;
+	state->gc.ngpio = NUM_GPIO;
+
+	/* it is output only */
+	state->gc.get = waveshare_gpio_gpio_get;
+	state->gc.set = waveshare_gpio_gpio_set;
+	state->gc.get_direction = waveshare_gpio_gpio_get_direction;
+	state->gc.can_sleep = true;
+
+	ret = devm_gpiochip_add_data(dev, &state->gc, state);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to create gpiochip\n");
+
+	props.type = BACKLIGHT_RAW;
+	props.max_brightness = 255;
+	props.brightness = 255;
+	bl = devm_backlight_device_register(dev, dev_name(dev), dev, state,
+					    &waveshare_gpio_bl, &props);
+	return PTR_ERR_OR_ZERO(bl);
+}
+
+static const struct of_device_id waveshare_gpio_dt_ids[] = {
+	{ .compatible = "waveshare,dsi-touch-gpio" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, waveshare_gpio_dt_ids);
+
+static struct i2c_driver waveshare_gpio_regulator_driver = {
+	.driver = {
+		.name = "waveshare-regulator",
+		.of_match_table = of_match_ptr(waveshare_gpio_dt_ids),
+	},
+	.probe = waveshare_gpio_probe,
+};
+
+module_i2c_driver(waveshare_gpio_regulator_driver);
+
+MODULE_DESCRIPTION("GPIO controller driver for Waveshare DSI touch panels");
+MODULE_LICENSE("GPL");