[alsa-devel] [PATCH] ALSA: hda - hdmi: Fix channel map switch not taking effect

[Takashi Iwai]

At Mon, 07 Oct 2013 15:09:15 +0200,
Takashi Iwai wrote:
> 
> At Mon, 07 Oct 2013 15:45:09 +0300,
> Anssi Hannula wrote:
> > 
> > Takashi Iwai kirjoitti 2013-10-07 13:43:
> > > At Mon, 07 Oct 2013 13:31:17 +0300,
> > > Anssi Hannula wrote:
> > > 
> > > Takashi Iwai kirjoitti 2013-10-07 10:48:
> > > > At Wed,  2 Oct 2013 21:13:32 +0300,
> > > > Anssi Hannula wrote:
> > > >
> > > > Currently hdmi_setup_audio_infoframe() reprograms the HDA channel
> > > > mapping only when the infoframe is not up-to-date or the non-PCM flag
> > > > has changed.
> > > >
> > > > However, when just the channel map has been changed, the infoframe may
> > > > still be up-to-date and non-PCM flag may not have changed, so the new
> > > > channel map is not actually programmed into the HDA codec.
> > > >
> > > > Notably, this failing case is also always triggered when the device is
> > > > already in a prepared state and a new channel map is configured while
> > > > changing only the channel positions (for example, plain
> > > > "speaker-test -c2 -m FR,FL").
> > > >
> > > > Fix that by keeping track of the last programmed channel map and making
> > > > hdmi_setup_audio_infoframe() always update the hardware mapping if the
> > > > channel map has changed.
> > > >
> > > > Hmm, maybe it's easier (and safer) to remove the check and always call
> > > > hdmi_setup_channel_mapping()?  Of course, the drawback is the
> > > > unnecessary verbs, but it's not too much.
> > > 
> > > Easier, yes. I don't really have that good of an idea how big of a 
> > > delay
> > > do 8 write verbs cause, so I'll rely on your judgment :)
> > > 
> > > I guess I could replace the writes with read-and-write-if-differs 
> > > cycles
> > > when I add the set_slot ops for ATI/AMD, since it seems to be used for
> > > other similar cases (like channel count)?
> > > 
> > > Well, this would result in more cost, as read requires a sync.
> > 
> > Hmm, so why does e.g. converter channel count set-up use that, then?
> 
> It can be optimized as well :)
> 
> > > If any, we can use the cached write/update.  But this assumes that the
> > > hardware never clears the value by some operation internally.
> > 
> > It should not, but better be safe than sorry here (at least for stable) 
> > :)
> > 
> > > > Signed-off-by: Anssi Hannula <anssi.hannula at iki.fi>
> > > > Cc: <stable at vger.kernel.org>
> > > > ---
> > > >
> > > > BTW, is there some mechanism preventing hdmi_chmap_ctl_put() to be
> > > > called
> > > > at the same time with generic_hdmi_playback_pcm_prepare() that I didn't
> > > > see with a quick look?
> > > > Both of them call hdmi_setup_audio_infoframe() which is not
> > > > thread-safe.
> > > >
> > > > Yeah, we need to introduce a mutex there.
> > > 
> > > I guess hdmi_present_sense() is the same, as it can also call
> > > hdmi_setup_audio_infoframe()?
> > > 
> > > Hm, looking at the code, we have already pin_eld->lock in
> > > hdmi_present_sense().  This can be used in other places, too.
> > 
> > Well, hdmi_setup_audio_infoframe() is non-threadsafe for other reasons 
> > than
> > eld as well (e.g. write verbs to hw), though, so it might be a bit 
> > confusing
> > as-is. Better move/rename the lock if we end up using it? Or not?
> 
> Yeah, it'd make sense.
> 
> > > (And pin_eld->monitor_present change at the beginning of
> > > hdmi_present_sense() should be protected in the mutex, too...)
> > > 
> > > BTW, shouldn't hdmi_present_sense() call hdmi_setup_audio_infoframe()
> > > always
> > > when eld_changed is true? hdmi_setup_audio_infoframe() does not do its
> > > stuff if !monitor_present, so if one starts playback before plugging 
> > > in,
> > > the channel mappings etc will never be set even when plug-in happens
> > > (from what I can see, that is -  did not test yet).
> > > 
> > > Well, there is such a call but currently specific to Haswell because
> > > it hasn't been tested for others.  Maybe we can simply get rid of
> > > is_haswell() check there.
> > 
> > OK, will test later and provide a patch if it works as expected.
> 
> Thanks.

[dropped stable from Cc]

Anssi, is the lock fix/cleanup patch ready?

I already have patche to extend mutex lock over other places and
move it into per_pin, but if you have already similar patches, I'll
take yours, hopefully together with other fixes.


thanks,

Takashi