Re: [alsa-devel] [PATCH 2/2] [RFC] ALSA: hda: hdmi - preserve non-MST PCM routing for Intel platforms

From: Kai Vehmanen <kai.vehmanen@linux.intel.com>
To: Takashi Iwai <tiwai@suse.de>
Cc: alsa-devel@alsa-project.org, Nikhil Mahale <nmahale@nvidia.com>,
	Kai Vehmanen <kai.vehmanen@linux.intel.com>
Subject: Re: [alsa-devel] [PATCH 2/2] [RFC] ALSA: hda: hdmi - preserve non-MST PCM routing for Intel platforms
Date: Fri, 29 Nov 2019 18:36:04 +0200 (EET)	[thread overview]
Message-ID: <alpine.DEB.2.21.1911291803050.16459@zeliteleevi> (raw)
In-Reply-To: <s5hsgm6ra98.wl-tiwai@suse.de>

Hey,

On Fri, 29 Nov 2019, Takashi Iwai wrote:

> On Fri, 29 Nov 2019 15:47:11 +0100, Kai Vehmanen wrote:
> > This second patch is however trickier. Nikhil your patch changed the 
> > default allocation a bit, so the routing might be difference also with 
> > snd-hda-intel (i.e. not SOF) for existing platforms and this may surprise 
> > users.
> 
> Well, but the allocation itself is dynamic for DP-MST, even on Intel,
> so user can't expect the completely persistent index assignment.
> That's the reason I took Nikhil's patch (even I suggested to simplify
> in that way).
[...]
> We had a trick to assign the primary index.  It still works, right?
> That should be the only concern.
[...]
> This is a platform-specific part, and on Intel, the assumption has
> been that pipe is equivalent with dev_id.  If this changed, of course,
> we must reconsider the whole picture.

hmm, the pipe equivalency should actually still hold. Looking at the code 
more, this could also be a lurking bug on graphics driver that had 
new side-effects with the recent ALSA side changes. E.g. I've received
logs where dev_id=1 is for a single connected HDMI monitor. I need to
investigate more whether this is an expected behaviour or a bug. :)

>> PS I did not have time to fully test the RFC patch, so this is just
>>    for discussion now...
> Since the assignment should work with your patch somehow, I already
> applied it.  Let's do fine tune-up during 5.5 rc cycles, if any.

Ack, ok. My commit message is a bit confusing (the wording about MST is 
not correct) but the actual code restores original behaviour so this 
should be good to apply. I'll continue testing and also dig a bit deeper 
into the bugreports w.r.t. what happens in the problematic non-MST cases. 
Thanks for the quick reviews!

Br, Kai
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