Re: [PATCH 4/5] fbdev: omap2: panel-dpi: allow specification of a reset gpio

[Tomi Valkeinen <tomi.valkeinen@ti.com>]

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On 10/12/15 15:11, Uwe Kleine-König wrote:
> From: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> 
> Some displays have a reset input. To assert that the display is
> functional the reset gpio must be deasserted.
> 
> Teach the driver to get and drive such a gpio accordingly.
> 
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> ---
>  Documentation/devicetree/bindings/video/panel-dpi.txt | 1 +
>  drivers/video/fbdev/omap2/displays-new/panel-dpi.c    | 7 +++++++
>  2 files changed, 8 insertions(+)

DT changes should be posted to devicetree@vger.kernel.org. And, I think,
the binding document changes are usually as a separate patch.

> diff --git a/Documentation/devicetree/bindings/video/panel-dpi.txt b/Documentation/devicetree/bindings/video/panel-dpi.txt
> index a40180b05bab..1a1d8f6f884f 100644
> --- a/Documentation/devicetree/bindings/video/panel-dpi.txt
> +++ b/Documentation/devicetree/bindings/video/panel-dpi.txt
> @@ -7,6 +7,7 @@ Required properties:
>  Optional properties:
>  - label: a symbolic name for the panel
>  - enable-gpios: panel enable gpio
> +- reset-gpios: GPIO to control the RESET pin
>  
>  Required nodes:
>  - "panel-timing" containing video timings
> diff --git a/drivers/video/fbdev/omap2/displays-new/panel-dpi.c b/drivers/video/fbdev/omap2/displays-new/panel-dpi.c
> index 1216341a0d19..7e2f9e0813dc 100644
> --- a/drivers/video/fbdev/omap2/displays-new/panel-dpi.c
> +++ b/drivers/video/fbdev/omap2/displays-new/panel-dpi.c
> @@ -32,6 +32,7 @@ struct panel_drv_data {
>  	int backlight_gpio;
>  
>  	struct gpio_desc *enable_gpio;
> +	struct gpio_desc *reset_gpio;
>  };
>  
>  #define to_panel_data(p) container_of(p, struct panel_drv_data, dssdev)
> @@ -83,6 +84,7 @@ static int panel_dpi_enable(struct omap_dss_device *dssdev)
>  	if (r)
>  		return r;
>  
> +	gpiod_set_value_cansleep(ddata->reset_gpio, 0);
>  	gpiod_set_value_cansleep(ddata->enable_gpio, 1);
>  
>  	if (gpio_is_valid(ddata->backlight_gpio))
> @@ -211,6 +213,11 @@ static int panel_dpi_probe_of(struct platform_device *pdev)
>  	if (IS_ERR(ddata->enable_gpio))
>  		return PTR_ERR(ddata->enable_gpio);
>  
> +	ddata->reset_gpio = devm_gpiod_get_optional(&pdev->dev,
> +						    "reset", GPIOD_OUT_HIGH);
> +	if (IS_ERR(ddata->reset_gpio))
> +		return PTR_ERR(ddata->reset_gpio);
> +
>  	ddata->backlight_gpio = -ENOENT;
>  
>  	r = of_get_display_timing(node, "panel-timing", &timing);
> 

This looks a bit odd to me. This only ever sets the reset gpio to 0, on
panel enable. If we never toggle the reset, it could be set to 0 at
probe time, right?

Reset is a bit tricky. I've seen panels where you have to have only a
short reset pulse (reset high, wait a short time, reset low). If you
leave the reset high, the panel draws extra power.

So I think the best we can do in a generic way is just to ensure the
reset is not asserted.

 Tomi


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