[alsa-devel] DP1.2 MST audio support discussion

[David Henningsson]

On 2015-10-22 08:56, Yang, Libin wrote:
>
>> -----Original Message-----
>> From: David Henningsson [mailto:david.henningsson at canonical.com]
>> Sent: Thursday, October 22, 2015 2:52 PM
>> To: Yang, Libin; Raymond Yau; Takashi Iwai
>> Cc: airlied at linux.ie; tanuk at iki.fi; Lin, Mengdong; Girdwood, Liam R;
>> ALSA Development Mailing List
>> Subject: Re: [alsa-devel] DP1.2 MST audio support discussion
>>
>>
>>
>> On 2015-10-22 03:31, Yang, Libin wrote:
>>> Hi Raymond,
>>>
>>>>
>>>> From: Raymond Yau [mailto:superquad.vortex2 at gmail.com]
>>>> Sent: Friday, October 16, 2015 8:33 AM
>>>> To: Takashi Iwai
>>>> Cc: airlied at linux.ie; tanuk at iki.fi; David Henningsson; Yang, Libin;
>> Lin,
>>>> Mengdong; Girdwood, Liam R; ALSA Development Mailing List
>>>> Subject: Re: [alsa-devel] DP1.2 MST audio support discussion
>>>>
>>>>
>>>>>>
>>>>>> Do it mean that only one DP MST port and no HDMI port on the
>>>> same graphic
>>>>>> card ?
>>>>>
>>>>> No.
>>>> If there is only one HDMI and one Display Port, this mean that there
>>>> are two pin complexes
>>>> How about the name of jack detection kctl of three Display Port
>>>> monitors  which are created on the same pin complex but different
>>>> dev_index ?
>>>
>>> For the jack name, what do you think if we change to
>>> "HDMI/DP, pin=n, dev=m" format? Will it impact on pulseaudio?
>>
>> Yes, it will impact PulseAudio. It will require changes to files in
>>
>> http://cgit.freedesktop.org/pulseaudio/pulseaudio/tree/src/modules/
>> alsa/mixer/paths
>
> So does this mean we should not change the name "HDMI/DP,pcm=3 Jack"
> to "HDMI/DP,pin=n, dev=m Jack", otherwise the old PA will not work with
> the new driver?

Yes. And I don't understand why you need to do it, either - if you have 
three display port monitors on one pin, then they will all get different 
PCMs (8, 9 and 10), and they will signal their Jack status through 
"HDMI/DP,pcm=8 Jack", "HDMI/DP,pcm=9 Jack" and "HDMI/DP,pcm=10 Jack".

Given that my proposed mapping algorithm will never change pin to PCM 
mapping (unless you have two displayport outputs and use MST on both), I 
think we can get away with not exposing the actual pin to userspace.
And should this later become necessary, we can add a separate kctl for that.

-- 
David Henningsson, Canonical Ltd.
https://launchpad.net/~diwic