[PATCHv3 3/5] dt-bindings: document the CEC GPIO bindings

[Linus Walleij]

On Wed, Aug 30, 2017 at 6:10 PM, Hans Verkuil <hverkuil at xs4all.nl> wrote:

> From: Hans Verkuil <hans.verkuil at cisco.com>
>
> Document the bindings for the cec-gpio module for hardware where the
> CEC pin and optionally the HPD pin are connected to GPIO pins.
>
> Signed-off-by: Hans Verkuil <hans.verkuil at cisco.com>

I usually refer to GPIO "lines" rather than "pins" for clarity.
It's because some systems also have pin control, and then it becomes
a bit muddy what is a pin.

> +* HDMI CEC GPIO driver
> +
> +The HDMI CEC GPIO module supports CEC implementations where the CEC pin
> +is hooked up to a pull-up GPIO pin and - optionally - the HPD pin is
> +hooked up to a pull-down GPIO pin.
> +
> +Required properties:
> +  - compatible: value must be "cec-gpio"
> +  - cec-gpio: gpio that the CEC line is connected to
> +
> +Optional property:
> +  - hpd-gpio: gpio that the HPD line is connected to
> +
> +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 {
> +       compatible = "cec-gpio";
> +       cec-gpio = <&gpio 7 GPIO_ACTIVE_HIGH>;
> +       hpd-gpio = <&gpio 17 GPIO_ACTIVE_HIGH>;
> +};

So what I understood from the driver is that the cec-gpio is maybe actually
an open drain output line, so in that case it should be stated in the docs and
cec-gpio  = <&gpio 7 GPIO_ACTIVE_HIGH|GPIO_OPEN_DRAIN>
or GPIO_LINE_OPEN_DRAIN if it is not also single-ended.


Yours,
Linus Walleij