[alsa-devel] [PATCH 00/11] drm/i915: LPE audio runtime PM and multipipe

[Ville Syrjälä]

On Wed, Apr 26, 2017 at 09:29:18AM +0200, Takashi Iwai wrote:
> On Tue, 25 Apr 2017 22:27:19 +0200,
> ville.syrjala at linux.intel.com wrote:
> > 
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > I was wondering why my VLV no longer runtime suspended, and after some
> > thinking I decided it had to be the LPE audio preventing it. Turns out
> > I was right, so here's my attempt at fixing it.
> > 
> > And while looking at the code I couldn't help but notice that it
> > couldn't actually handle multiple pipes playing back audio at the
> > same time. And even having multiple displays active even if only
> > one was playing audio was probably a recipe for failure. So I
> > tried to fix that by registering a separate PCM device for each
> > pipe.
> > 
> > Note that the patch subjects may not reflect the subsystem
> > very well since most of these straddle the border between drm
> > and alsa. I think I just slapped on drm/i915 to most where
> > there was no clear winner.
> 
> A nice patchset, thanks for working on it!
> 
> One slight concern (other than the jack issue Pierre reported) is the
> incompatible behavior from the current version.  With the pipe-based
> multiple streams, user would need to choose another one even if the
> device has a single HDMI output, which is pretty common on BYT/CHV
> tablets.
> 
> Maybe it's no big problem as the users are still limited at the
> moment.  Or, we may need to handle a bit differently, e.g. assigning
> the PCM stream dynamically per hotplug.

Yeah, I tied the PCM device to the pipe to match the hardware. But we
could certainly register the PCM device per port, and then do a 
pipe<->port mapping somewhere to make it all work out. One slight
complication is that not all ports are necessarily present so we
might have eg. just port B and port D, but no port C. Not sure if
it would be a bad thing to register a PCM device even for the
missing ports anyway?

I don't recall which way HDA works. Device per port I guess? Well,
for DP SST/HDMI. But for DP MST I presume it's device per stream
(ie. pipe) even with HDA.

> In anyway, with the support of multi streams, alsa-lib config needs to
> be updated.

Hmm. I suppose I'll have to take a gander at what's there.

-- 
Ville Syrjälä
Intel OTC