[RFC PATCH 7/7] drm/i915: add DisplayPort CEC-Tunneling-over-AUX support

[Clint Taylor]

On 05/30/2017 12:11 AM, Jani Nikula wrote:
> On Tue, 30 May 2017, Hans Verkuil <hverkuil at xs4all.nl> wrote:
>> On 05/29/2017 09:00 PM, Daniel Vetter wrote:
>>> On Fri, May 26, 2017 at 12:20:48PM +0200, Hans Verkuil wrote:
>>>> On 05/26/2017 09:15 AM, Daniel Vetter wrote:
>>>>> Did you look into also wiring this up for dp mst chains?
>>>> Isn't this sufficient? I have no way of testing mst chains.
>>>>
>>>> I think I need some pointers from you, since I am a complete newbie when it
>>>> comes to mst.
>>> I don't really have more clue, but yeah if you don't have an mst thing (a
>>> simple dp port multiplexer is what I use for testing here, then plug in a
>>> converter dongle or cable into that) then probably better to not wire up
>>> the code for it.
>> I think my NUC already uses mst internally. But I was planning on buying a
>> dp multiplexer to make sure there is nothing special I need to do for mst.
>>
>> The CEC Tunneling is all in the branch device, so if I understand things
>> correctly it is not affected by mst.
>>
>> BTW, I did a bit more testing on my NUC7i5BNK: for the HDMI output they
>> use a MegaChip MCDP2800 DP-to-HDMI converter which according to their
>> datasheet is supposed to implement CEC Tunneling, but if they do it is not
>> exposed as a capability. I'm not sure if it is a MegaChip firmware issue
>> or something else. The BIOS is able to do some CEC, but whether they hook
>> into the MegaChip or have the CEC pin connected to a GPIO or something and
>> have their own controller is something I do not know.
>>
>> If anyone can clarify what Intel did on the NUC, then that would be very
>> helpful.
> It's called LSPCON, see i915/intel_lspcon.c, basically to support HDMI
> 2.0. Currently we only use it in PCON mode, shows up as DP for us. It
> could be used in LS mode, showing up as HDMI 1.4, but we don't support
> that in i915.
>
> I don't know about the CEC on that.

My NUC6i7KYK has the MCDP2850 LSPCON and it does support CEC over Aux. 
The release notes for the NUC state that there is a BIOS configuration 
option for enabling support. My doesn't have the option but the LSPCON 
fully supports CEC.

-Clint

>
>
> BR,
> Jani.
>
>> It would be so nice to get MegaChip CEC Tunneling working on the NUC, because
>> then you have native CEC support without requiring any Pulse Eight adapter.
>>
>> And add a CEC-capable USB-C to HDMI adapter and you have it on the USB-C
>> output as well.
>>
>> Regards,
>>
>> 	Hans