[PATCHv4 3/5] dt-bindings: document the CEC GPIO bindings

[Rob Herring]

On Thu, Aug 31, 2017 at 01:01:54PM +0200, Hans Verkuil wrote:
> From: Hans Verkuil <hans.verkuil at cisco.com>
> 
> Document the bindings for the cec-gpio module for hardware where the
> CEC line and optionally the HPD line are connected to GPIO lines.
> 
> Signed-off-by: Hans Verkuil <hans.verkuil at cisco.com>
> ---
>  .../devicetree/bindings/media/cec-gpio.txt         | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/media/cec-gpio.txt
> 
> diff --git a/Documentation/devicetree/bindings/media/cec-gpio.txt b/Documentation/devicetree/bindings/media/cec-gpio.txt
> new file mode 100644
> index 000000000000..db20a7452dbd
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/media/cec-gpio.txt
> @@ -0,0 +1,22 @@
> +* HDMI CEC GPIO driver
> +
> +The HDMI CEC GPIO module supports CEC implementations where the CEC line
> +is hooked up to a pull-up GPIO line and - optionally - the HPD line is
> +hooked up to another GPIO line.
> +
> +Required properties:
> +  - compatible: value must be "cec-gpio"
> +  - cec-gpio: gpio that the CEC line is connected to

cec-gpios

> +
> +Optional property:
> +  - hpd-gpio: gpio that the HPD line is connected to

hpd-gpios

However, HPD is already part of the HDMI connector binding. Having it in 
2 places would be wrong.

I think we should have either:

hdmi-connector {
	compatible = 'hdmi-connector-a";
	hpd-gpios = <...>;
	cec-gpios = <...>;
	ports {
		// port to HDMI controller
	...
	};
};

Or:

hdmi-connector {
        compatible = 'hdmi-connector-a";
        hpd-gpios = <...>;
        cec = <&cec>;
        ... 
};

cec: cec-gpio {
	compatible = "cec-gpio";
	cec-gpios = <...>;
};

My preference is probably the former. The latter just helps create a 
device to bind to a driver, but DT is not the only way to create 
devices. Then again, if you have a phandle to real CEC controllers in 
the HDMI connector node, it may make sense to do the same thing with 
cec-gpio. 

> +
> +Example for the Raspberry Pi 3 where the CEC line is connected to
> +pin 26 aka BCM7 aka CE1 on the GPIO pin header and the HPD line is
> +connected to pin 11 aka BCM17:
> +
> +cec-gpio at 7 {

unit address is not valid. Build your dts's with W=2.

> +       compatible = "cec-gpio";
> +       cec-gpio = <&gpio 7 GPIO_OPEN_DRAIN>;
> +       hpd-gpio = <&gpio 17 GPIO_ACTIVE_HIGH>;
> +};
> -- 
> 2.14.1
> 
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