Re: [alsa-devel] [PATCH 11/11] ALSA: x86: Register multiple PCM devices for the LPE audio card

From: Takashi Iwai <tiwai@suse.de>
To: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org, alsa-devel@alsa-project.org
Subject: Re: [alsa-devel] [PATCH 11/11] ALSA: x86: Register multiple PCM devices for the LPE audio card
Date: Wed, 26 Apr 2017 16:04:25 +0200	[thread overview]
Message-ID: <s5hinlr5kpi.wl-tiwai@suse.de> (raw)
In-Reply-To: <20170426134906.GU30290@intel.com>

On Wed, 26 Apr 2017 15:49:06 +0200,
Ville Syrjälä wrote:
> 
> On Wed, Apr 26, 2017 at 09:19:21AM +0200, Takashi Iwai wrote:
> > On Wed, 26 Apr 2017 09:04:46 +0200,
> > Takashi Iwai wrote:
> > > 
> > > On Wed, 26 Apr 2017 03:58:57 +0200,
> > > Pierre-Louis Bossart wrote:
> > > > 
> > > > On 04/25/2017 03:27 PM, ville.syrjala@linux.intel.com wrote:
> > > > > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > > >
> > > > > Now that everything is in place let's register a PCM device for
> > > > > each pipe of the display engine. This will make it possible to
> > > > > actually output audio to multiple displays at the same time. And
> > > > > it avoids modesets on unrelated displays from clobbering up the
> > > > > ELD and whatnot for the display currently doing the playback.
> > > > >
> > > > > The alternative would be to have a PCM device per port, but per-pipe
> > > > > is easier since the hardware actually works that way.
> > > > Very nice. I just tested on a CHT Zotac box which has two connectors
> > > > (1 HDMI and 1 DP), and I get sound concurrently on both, with hdmi
> > > > being listed as device 2 and DP as device 0.
> > > > I thought there were hardware restrictions but you proved me wrong. Kudos.
> > > > 
> > > > The only point that I find weird is that the jacks are reported as
> > > > 'on' on the 3 pipes, is there a way to tie them to an actual cable
> > > > being used?
> > > 
> > > The pdata check was changed to check port=-1 as the monitor off in the
> > > patch 6.  Maybe the initialization is missing?
> > 
> > I guess the problem is that the hotplug wq is called at the
> > initialization to retrieve the pdata for all pipes.  It's called with
> > uninitialized port=0, so all flags are on at init.
> 
> Indeed. That will need to be fixed.
> 
> > 
> > And it implies the potential problem: the pdata contains the
> > information only for a single pipe.  Maybe it should keep the
> > status/ELD for all three pipes.
> 
> I already did that.

Oh then it' fine, I just didn't find it.

> That being said, the entire notify vs. wq is pretty racy. So I was
> thinking that maybe we could just eliminate the wq and do whatever is
> needed directly from the notify hook. And then we could eliminate the
> (ab)use of pdata to transfer the ELD and whatnot between the drivers.
> I guess the main complication is the driver load case. I didn't
> really think that one through so far.

One way would be to implement the get_eld() to call at the probe
time.  HD-audio calls such one (provided via component) at probe and
resume time to sync with the actual h/w state.  For LPE audio, it's
even easier, as we may call i915 exported function directly.

thanks,

Takashi
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