On Fri, Sep 15, 2017 at 3:40 AM, Hans Verkuil <hverkuil@xxxxxxxxx> wrote: > Hi Rob, > > On 09/13/17 10:21, Hans Verkuil wrote: >> On 09/12/2017 04:43 PM, Rob Herring wrote: >>> On Thu, Aug 31, 2017 at 01:01:54PM +0200, Hans Verkuil wrote: >>>> From: Hans Verkuil <hans.verkuil@xxxxxxxxx> >>>> >>>> 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@xxxxxxxxx> >>>> --- >>>> .../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 >> >> Will change. >> >>> >>>> + >>>> +Optional property: >>>> + - hpd-gpio: gpio that the HPD line is connected to >>> >>> hpd-gpios >> >> Will change. >> >>> >>> However, HPD is already part of the HDMI connector binding. Having it in >>> 2 places would be wrong. >> >> No. This is not an HDMI receiver/transmitter. There are two use-cases for this >> driver: >> >> 1) For HDMI receivers/transmitters that connect the CEC pin of an HDMI connector >> to a GPIO pin. In that case the HPD goes to the HDMI transmitter/receiver and >> not to this driver. As you say, that would not make any sense. >> >> But currently no such devices are in the kernel (I know they exist, though). >> Once such a driver would appear in the kernel then these bindings need to be >> extended with an hdmi-phandle. >> >> 2) This driver is used for debugging CEC like this: >> >> https://hverkuil.home.xs4all.nl/rpi3-cec.jpg >> >> Here the CEC pin of an HDMI breakout connector is hooked up to a Raspberry Pi >> GPIO pin and the RPi monitors it. It's a cheap but very effective CEC analyzer. >> In this use-case it is very helpful to also monitor the HPD pin since some >> displays do weird things with the HPD and knowing the state of the HPD helps >> a lot when debugging CEC problems. It's optional and it only monitors the pin. >> >> Actually, there does not have to be an HDMI connector involved at all: you can >> make two cec-gpio instances and just connect the two GPIO pins together in >> order to emulate two CEC adapters and play with that. > > Is it OK to define a binding but not (yet) implement it? I have seen that in other > bindings (well, OK, one other binding :-) ). If that is fine, then I can write the > following: It's preferred over adding a property one by one. > > ---------------------------------------------------------------- > Required properties: > - compatible: value must be "cec-gpio". > - cec-gpios: gpio that the CEC line is connected to. > > If the CEC line is associated with an HDMI receiver/transmitter, then the following > property is also required: > > - hdmi-phandle - phandle to the HDMI controller, see also cec.txt. > > If the CEC line is not associated with an HDMI receiver/transmitter, then the > following property is optional: > > - hpd-gpios: gpio that the HPD line is connected to. > ---------------------------------------------------------------- Yes, this seems fine. Rob
