[PATCHv2 1/3] dt-bindings: display: dw_hdmi.txt: add cec-disable property

Hans Verkuil hverkuil at xs4all.nl
Mon Jul 2 02:02:48 PDT 2018

On 29/06/18 09:17, Neil Armstrong wrote:
> Hi Hans,
> On 03/04/2018 10:27, Hans Verkuil wrote:
>> On 27/03/18 00:25, Rob Herring wrote:
>>> On Fri, Mar 23, 2018 at 01:59:13PM +0100, Hans Verkuil wrote:
>>>> From: Hans Verkuil <hans.verkuil at cisco.com>
>>>> Some boards have both a DesignWare and their own CEC controller.
>>>> The CEC pin is only hooked up to their own CEC controller and not
>>>> to the DW controller.
>>>> Add the cec-disable property to disable the DW CEC controller.
>>>> This particular situation happens on Amlogic boards that have their
>>>> own meson CEC controller.
>>> Seems like we could avoid this by describing how the CEC line is hooked 
>>> up which could be needed for other reasons.
>> So there are three situations:
>> 1) The cec pin is connected to the DW HDMI TX. That's already supported.
>> 2) The cec pin is not connected at all, but the CEC IP is instantiated.
>>    We need the cec-disable property for that. This simply states that the
>>    CEC pin is not connected.
>> 3) The cec pin is connected to an HDMI RX. We do not support this at the
>>    moment. If we want to support this, then we need a 'hdmi-rx' phandle
>>    that points to the HDMI receiver that the CEC pin is associated with.
>>    This will be similar to the already existing 'hdmi-phandle' property
>>    used to associate a CEC driver with an HDMI transmitter. In hindsight
>>    it would have been better if 'hdmi-phandle' was named 'hdmi-tx' :-(
>> I can make a binding proposal for 3, but I have no hardware to test it,
>> so I think it is better to add this only when someone has hardware. It
>> will require quite a few changes to the driver and likely also the CEC core.
> Can't we simply add a property to override the HW config fields in this case ?
> It will be then usable with any feature the is enabled by reading the config
> bits like AHB Audio, I2c, CEC, ... and maybe many more in the future.

Yes, we can do that as well. But is that a proper description of the hardware?
The HW *does* support CEC, but in this case the CEC line is just not hooked
up to anything. So overriding the HW config field doesn't really sound right
to me.

I still believe that the cec-disable property in order to describe situation
2 in the list above is the right approach.

Perhaps giving it a different name (cec-not-connected?) helps overcome Rob's
objections? Rob?

Sorry for not following up on this earlier.



> Neil
>> Regards,
>> 	Hans
>>>> Signed-off-by: Hans Verkuil <hans.verkuil at cisco.com>
>>>> Acked-by: Neil Armstrong <narmstrong at baylibre.com>
>>>> ---
>>>>  Documentation/devicetree/bindings/display/bridge/dw_hdmi.txt | 3 +++
>>>>  1 file changed, 3 insertions(+)
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