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

[Liam Girdwood]

On Fri, 2015-06-26 at 11:50 +0100, Kaskinen, Tanu wrote:
> 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? 

It's generally ready when the PCM is created iirc.

> 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.
> 

I agree, adding mixers first make sense.

Liam