[alsa-devel] [PATCH] ALSA: hda: Disable odd numbered channels on HDMI controllers.

[Takashi Iwai]

At Thu, 13 Jan 2011 22:42:39 +0200,
Anssi Hannula wrote:
> 
> On 13.01.2011 22:19, Nitin Daga wrote:
> > Added code in hda_intel.c to disable odd numbered channels
> > not supported by HDMI controllers.
> > 
> > Signed-off-by: Nitin Daga <ndaga at nvidia.com>
> > Acked-By: Stephen Warren <swarren at nvidia.com>
> > ---
> >  pci/hda/hda_intel.c |   13 +++++++++++++
> >  1 files changed, 13 insertions(+), 0 deletions(-)
> > 
> > diff --git a/pci/hda/hda_intel.c b/pci/hda/hda_intel.c
> > index a78ea34..293c685 100644
> > --- a/pci/hda/hda_intel.c
> > +++ b/pci/hda/hda_intel.c
> > @@ -1539,6 +1539,16 @@ struct azx_pcm {
> >  	struct hda_pcm_stream *hinfo[2];
> >  };
> >  
> > +static unsigned int channels_2_4_6_8[] = {
> > +	2, 4, 6, 8
> > +};
> > +
> > +static struct snd_pcm_hw_constraint_list hw_constraints_2_4_6_8_channels = {
> > +	.count = ARRAY_SIZE(channels_2_4_6_8),
> > +	.list = channels_2_4_6_8,
> > +	.mask = 0,
> > +};
> 
> Hmm, can't these be const? OTOH none of the other drivers use const for
> snd_pcm_hw_constraint_list either, so I guess it is ok.
> 
> >  static int azx_pcm_open(struct snd_pcm_substream *substream)
> >  {
> >  	struct azx_pcm *apcm = snd_pcm_substream_chip(substream);
> > @@ -1566,6 +1576,9 @@ static int azx_pcm_open(struct snd_pcm_substream *substream)
> >  				   128);
> >  	snd_pcm_hw_constraint_step(runtime, 0, SNDRV_PCM_HW_PARAM_PERIOD_BYTES,
> >  				   128);
> > +	snd_pcm_hw_constraint_list(runtime, 0,
> > +				   SNDRV_PCM_HW_PARAM_CHANNELS,
> > +				   &hw_constraints_2_4_6_8_channels);
> 
> This would seem simpler and more generic (there are codecs that have
> over 8 channels):
> snd_pcm_hw_constraint_step(runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS, 2);
> 
> However, either of those would AFAICS break Si3054 Modem codec which is
> mono-only.
> 
> Maybe just add the constraint to patch_hdmi.c?

Yes, looks so.  I applied the following patch instead.

Alternatively, we can check channels_min and channels_max that are
already set in hda_intel.c::azx_pcm_open(), and apply the hw_constraint
only when channels_min%2==0 or such.

But, as we aren't 100% sure whether the odd number of channels work
with other (analog) codecs, it's safer to limit only for HDMI for the
time being.


thanks,

Takashi

---
From ad09fc9d2156f3d37537b34418a6b79309013d33 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai at suse.de>
Date: Fri, 14 Jan 2011 09:42:27 +0100
Subject: [PATCH] ALSA: hda - Suppress the odd number of channels for HDMI

It looks like that HDMI codecs don't support the odd number of channels
although HD-audio spec doesn't have the restriction.  Add the
hw_constraint to limit to only the even number of channels.

Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/pci/hda/patch_hdmi.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/sound/pci/hda/patch_hdmi.c b/sound/pci/hda/patch_hdmi.c
index f29b97b..2d28879 100644
--- a/sound/pci/hda/patch_hdmi.c
+++ b/sound/pci/hda/patch_hdmi.c
@@ -1238,6 +1238,9 @@ static int simple_playback_pcm_open(struct hda_pcm_stream *hinfo,
 		snd_pcm_hw_constraint_list(substream->runtime, 0,
 				SNDRV_PCM_HW_PARAM_CHANNELS,
 				hw_constraints_channels);
+	} else {
+		snd_pcm_hw_constraint_step(substream->runtime, 0,
+					   SNDRV_PCM_HW_PARAM_CHANNELS, 2);
 	}
 
 	return snd_hda_multi_out_dig_open(codec, &spec->multiout);
-- 
1.7.3.4