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

From: Jani Nikula <jani.nikula@intel.com>
To: Hans Verkuil <hverkuil@xs4all.nl>, Daniel Vetter <daniel@ffwll.ch>
Cc: linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org,
	intel-gfx@lists.freedesktop.org,
	Clint Taylor <clinton.a.taylor@intel.com>,
	Hans Verkuil <hans.verkuil@cisco.com>
Subject: Re: [RFC PATCH 7/7] drm/i915: add DisplayPort CEC-Tunneling-over-AUX support
Date: Tue, 30 May 2017 10:11:53 +0300	[thread overview]
Message-ID: <87y3tekedi.fsf@intel.com> (raw)
In-Reply-To: <d9e9354b-eeb7-0a1e-2dbc-16c1ba0c0784@xs4all.nl>

On Tue, 30 May 2017, Hans Verkuil <hverkuil@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.

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

-- 
Jani Nikula, Intel Open Source Technology Center