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

[Linus Walleij]

Hi Dmitry,

On Sat, Apr 11, 2026 at 2:11 PM Dmitry Baryshkov
<dmitry.baryshkov@xxxxxxxxxxxxxxxx> 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@xxxxxxxxxx>
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
(...)

> +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);

Why is this not just flagging the same register as write-only
in the regmap and just re-reading that same register from the
regmap cache?

> +
> +       return !!pwr_state;
> +}

OK so it's write-only.

> +static int waveshare_gpio_set(struct waveshare_gpio *state, unsigned int offset, int value)

This looks like it can be replaced with a few lines of
select GPIO_REGMAP
#include <linux/gpio/regmap.h>
helpers.

Has this not been discussed earlier?

Yours,
Linus Walleij