linux-kernel - Re: [PATCH v2 1/8] drm/bridge: rgb-to-vga: Support an enable GPIO

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Date:   Wed, 26 Oct 2016 17:13:46 -0500
From:   Rob Herring <robh@...nel.org>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Maxime Ripard <maxime.ripard@...e-electrons.com>,
        David Airlie <airlied@...ux.ie>,
        Mark Rutland <mark.rutland@....com>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-sunxi@...glegroups.com
Subject: Re: [PATCH v2 1/8] drm/bridge: rgb-to-vga: Support an enable GPIO

On Thu, Oct 20, 2016 at 11:43:37AM +0800, Chen-Yu Tsai wrote:
> Some rgb-to-vga bridges have an enable GPIO, either directly tied to
> an enable pin on the bridge IC, or indirectly controlling a power
> switch.
> 
> Add support for it.
> 
> Signed-off-by: Chen-Yu Tsai <wens@...e.org>
> ---
>  .../bindings/display/bridge/dumb-vga-dac.txt       |  2 ++
>  drivers/gpu/drm/bridge/dumb-vga-dac.c              | 28 ++++++++++++++++++++++
>  2 files changed, 30 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/display/bridge/dumb-vga-dac.txt b/Documentation/devicetree/bindings/display/bridge/dumb-vga-dac.txt
> index 003bc246a270..d3484822bf77 100644
> --- a/Documentation/devicetree/bindings/display/bridge/dumb-vga-dac.txt
> +++ b/Documentation/devicetree/bindings/display/bridge/dumb-vga-dac.txt
> @@ -16,6 +16,8 @@ graph bindings specified in Documentation/devicetree/bindings/graph.txt.
>  - Video port 0 for RGB input
>  - Video port 1 for VGA output
>  
> +Optional properties:
> +- enable-gpios: GPIO pin to enable or disable the bridge

This should also define the active state.

> +static void dumb_vga_enable(struct drm_bridge *bridge)
> +{
> +	struct dumb_vga *vga = drm_bridge_to_dumb_vga(bridge);
> +
> +	if (vga->enable_gpio)
> +		gpiod_set_value_cansleep(vga->enable_gpio, 1);

So the driver should allow either active high or low.

> +}
> +
> +static void dumb_vga_disable(struct drm_bridge *bridge)
> +{
> +	struct dumb_vga *vga = drm_bridge_to_dumb_vga(bridge);
> +
> +	if (vga->enable_gpio)
> +		gpiod_set_value_cansleep(vga->enable_gpio, 0);
> +}
> +