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

From: Hans Verkuil <hverkuil@xs4all.nl>
To: Clint Taylor <clinton.a.taylor@intel.com>,
	Jani Nikula <jani.nikula@intel.com>,
	Daniel Vetter <daniel@ffwll.ch>
Cc: intel-gfx@lists.freedesktop.org,
	Hans Verkuil <hans.verkuil@cisco.com>,
	dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org
Subject: Re: [RFC PATCH 7/7] drm/i915: add DisplayPort CEC-Tunneling-over-AUX support
Date: Tue, 30 May 2017 18:54:30 +0200	[thread overview]
Message-ID: <8150d62a-ecbc-6235-5595-1764fe616d8b@xs4all.nl> (raw)
In-Reply-To: <22961af9-5157-ae14-3000-f91cedc27958@xs4all.nl>

On 05/30/2017 06:49 PM, Hans Verkuil wrote:
> On 05/30/2017 04:19 PM, Clint Taylor wrote:
>>
>>
>> On 05/30/2017 12:11 AM, Jani Nikula wrote:
>>> 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.
>>
>> 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.
> 
> What is the output of:
> 
> dd if=/dev/drm_dp_aux0 of=aux0 skip=12288 ibs=1 count=48
> od -t x1 aux0
> 
> Assuming drm_dp_aux0 is the aux channel for the HDMI output on your NUC.
> 
> If the first byte is != 0x00, then it advertises CEC over Aux.
> 
> For me it says 0x00.
> 
> When you say "it does support CEC over Aux", does that mean you have actually
> tested it somehow? The only working solution I have seen mentioned for the
> NUC6i7KYK is a Pulse-Eight adapter.
> 
> With the NUC7i Intel made BIOS support for CEC, but it is not at all
> clear to me if they used CEC tunneling or just hooked up the CEC pin to
> some microcontroller.
> 
> The only working chipset I have seen is the Parade PS176.

If it really is working on your NUC, then can you add the output of
/sys/kernel/debug/dri/0/i915_display_info?

Thanks,

	Hans