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

[Takashi Iwai]

On Fri, 16 Oct 2015 10:51:30 +0200,
Yang, Libin wrote:
> 
> Hi Takashi,
> 
> > -----Original Message-----
> > From: Takashi Iwai [mailto:tiwai at suse.de]
> > Sent: Friday, October 16, 2015 2:38 PM
> > To: Raymond Yau
> > Cc: Yang, Libin; ALSA Development Mailing List; airlied at linux.ie; Lin,
> > Mengdong; Girdwood, Liam R; tanuk at iki.fi; David Henningsson
> > Subject: Re: [alsa-devel] DP1.2 MST audio support discussion
> > 
> > On Fri, 16 Oct 2015 02:32:50 +0200,
> > Raymond Yau wrote:
> > >
> > > > >
> > > > > 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
> > 
> > Yes, and the mapping doesn't change in this case as before.
> > 
> > > 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 ?
> > 
> > It's one of the models we've considered.  Basically the number of
> > devices can be up to 64 (or such) per pin.  For Intel case, due to the
> > limitation of converters, it's up to 3.  For other GPUs that may drive
> > more simultaneous outputs, the number increases in square.  If a GPU
> > may handle 16 outputs, it'll be 256 entries.
> > 
> > Although the 256 entries are certainly manageable as kctl, whether
> > this is the best representation for user-space is a question.
> 
> This is what I concern. Each device entry should have one tag
> for unsol event. This means each device entry will create a jack?

Yes, and essentially each entry corresponds to a PCM, so we'll end up
with 256 PCM (sub)streams :)  This doesn't scale.

So, thinking of this issue again, I'm convinced now that static PCM
entries with extra dynamic PCM slots as David suggested would work
more safely.  The number of dynamic PCMs can be either a fixed number
per driver type, a constant, or variable via module option.


Takashi