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

[Kaskinen, Tanu]

On Tue, 2015-06-23 at 10:51 +0300, Tanu Kaskinen wrote:
> (Added pulseaudio-discuss to CC.)
> 
> On Mon, 2015-06-22 at 17:44 +0200, Takashi Iwai wrote:
> > At Mon, 22 Jun 2015 15:21:16 +0000,
> > Kaskinen, Tanu wrote:
> > > 
> > > On Mon, 2015-06-22 at 14:29 +0100, Liam Girdwood wrote:
> > > > Btw, the topology core now also dynamically
> > > > creates/removes mixer controls, can PA handle this atm ?
> > > 
> > > No, PA checks the mixer controls only when loading a new card.
> > > Dynamically added controls are ignored. Dynamically removed controls
> > > just cause silent failure, at least when setting volume (I didn't check
> > > other use cases). That is, changing the volume appears to succeed, but
> > > nothing actually happens.
> > 
> > Won't PA use ELD or other information?  The corresponding controls to
> > HDMI/DP will be created / deleted dynamically together with a PCM
> > device, I suppose.
> 
> Yes, PA uses ELD. If mixer controls become dynamic too, then that's
> another thing to implement.

Liam, how does the userspace know when the new PCM is ready to use? If
new mixer controls are added too, it has to be defined which gets
created first: the PCM device or the mixer controls. I think it would be
best if the mixer controls get created first, and when the new PCM
device appears, it's immediately fully ready to be used.

-- 
Tanu