[alsa-devel] [Intel-gfx] [PATCH 3/4] snd: add support for displayport multi-stream to hda codec.

[Raymond Yau]

2015-6-29 下午3:58於 "Jani Nikula" <jani.nikula at linux.intel.com>寫道：
>
> On Sat, 27 Jun 2015, Raymond Yau <superquad.vortex2 at gmail.com> wrote:
> >> > >
> >> > > Shall we move or cc this discussion on audio driver side to ALSA
ML?
> >> >
> >> > Oops I thought I had cc'ed these patches to alsa-devel as well when I
> > sent them.
> >> >
> >> > > I think we also need to decide how to manage PCM devices for DP
MST.
> >> > > Now the HD-A driver create a PCM device for each pin, and the
> > substream
> >> > > number is 1 for each PCM. Now with DP MST enabled, each pin can
> > support
> >> > > multiple streams (e.g. 3 on Intel HSW/BDW/SKL).
> >> > >
> >> > > There may be 2 options:
> >> > > -#1: Let an HDMI codec specify number of substreams, same as the
> > number
> >> > > of device entries on a pin. We can specify 3 for HSW/BDW/SKL. Other
> >> > > vendors can also specify a value according to actual HW
capabilities.
> >> > >
> >> > > So for HSW, we have 3x3 subtreams totally. But we only have 3
> > convertors
> >> > > (for 3 display pipelines), so we can open up to 3 substreams at the
> > same
> >> > > time. When the audio driver finds all 3 convertors are used when
> > opening
> >> > > a new substream, it will fail.
> >> >
> >> > One thing I noticed is the number of devices on a PIN is only updated
> > when
> >> > the MST device is plugged in so normally pins 5,6,7 have 0 devices,
and
> > when
> >> > I plug in MST device, I get the 3 devices on port 6. So it seems
dynamic
> >> > enough at this point, though I guess it'll always be 0 or 3.
> >> > >
> >> > > - #2: Create PCM device dynamically. Only create a PCM devices for
a
> > device
> >> > > entry which connects to monitor with audio support. When the
monitor
> >> > > is removed, the PCM device will be disconnected, closed and
removed,
> >> > > similar to the USB case.
> >
> > Do the driver really need dynamic PCM since display ports are dasiy
chained
> > and the locations within the dasiy chain are fixed ?

http://www.intel.com/support/motherboards/desktop/sb/CS-034199.htm

Do the first display always support sound since hdmi can connect to tv
using dvi ?

As Pulseaudio does not support multi streaming ( playing different audio
streams to headphone and rear panel speakers , how can pulseaudion support
displayport MST ?