Re: [PATCH v2 21/21] gpio: add GPIO controller found on Waveshare DSI TOUCH panels

[Jie Gan <jie.gan@oss.qualcomm.com>]

On 4/11/2026 8:10 PM, Dmitry Baryshkov wrote:
> 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>
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
> ---
>   drivers/gpio/Kconfig              |  10 ++
>   drivers/gpio/Makefile             |   1 +
>   drivers/gpio/gpio-waveshare-dsi.c | 208 ++++++++++++++++++++++++++++++++++++++
>   3 files changed, 219 insertions(+)
> 
> diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
> index dbe7c6e63eab..1b210c451151 100644
> --- a/drivers/gpio/Kconfig
> +++ b/drivers/gpio/Kconfig
> @@ -805,6 +805,16 @@ 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 Technologies Inc WCD9340/WCD9341 GPIO controller driver"
>   	depends on MFD_WCD934X
> diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
> index 20d4a57afdaa..75ce89fc3b93 100644
> --- a/drivers/gpio/Makefile
> +++ b/drivers/gpio/Makefile
> @@ -207,6 +207,7 @@ 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
> diff --git a/drivers/gpio/gpio-waveshare-dsi.c b/drivers/gpio/gpio-waveshare-dsi.c
> new file mode 100644
> index 000000000000..f4a1d4d3b872
> --- /dev/null
> +++ b/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_PWM,

.max_register = REG_VERSION,

check comments in probe

> +};
> +
> +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);

for waveshare_gpio_regmap_config: .max_register = REG_PWM,

> +	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);

REG_ID here is 0x98,

in _regmap_read -> regmap_readable will check the max_register, then 
return -EIO.

> +	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);

ditto.

Thanks,
Jie

> +	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");
>