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: ---------------------------------------------------------------- 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. ---------------------------------------------------------------- I have plans to support hdmi-phandle in the driver, but that probably won't be ready in time for 4.15. Regards, Hans > >> >> 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@7 { >> >> unit address is not valid. Build your dts's with W=2. > > I'll do that. > >> >>> + compatible = "cec-gpio"; >>> + cec-gpio = <&gpio 7 GPIO_OPEN_DRAIN>; >>> + hpd-gpio = <&gpio 17 GPIO_ACTIVE_HIGH>; >>> +}; >>> -- >>> 2.14.1 > > Regards, > > Hans >
