[alsa-devel] Missing surround channels with Nvidia HDMI & snd-hda-intel driver

[Takashi Iwai]

On Fri, 17 Nov 2017 09:28:55 +0100,
VDR User wrote:
> 
> Hi Takashi,
> 
> I can confirm that your patch does fix the bug:
> 
> [ao/alsa] trying to set ALSA channel map: FL FR FC LFE RL RR
> [ao/alsa] channel map reported by ALSA: FL FR FC LFE RL RR
> [ao/alsa] which we understand as: 5.1
> 
> /usr/src/linux$ uname -r
> 4.14.0-amd
> /usr/src/linux$ speaker-test -c 6 -t wav
> 
> speaker-test 1.1.3
> 
> Playback device is default
> Stream parameters are 48000Hz, S16_LE, 6 channels
> WAV file(s)
> Rate set to 48000Hz (requested 48000Hz)
> Buffer size range from 64 to 5440
> Period size range from 32 to 2720
> Using max buffer size 5440
> Periods = 4
> was set period_size = 1088
> was set buffer_size = 5440
>  0 - Front Left
>  4 - Front Center
>  1 - Front Right
>  3 - Rear Right
>  2 - Rear Left
>  5 - LFE
> Time per period = 8.525875
> 
> Thank you for all your help to resolve this bug!

Great, thanks for your patient testing!
FWIW, below is the patch I'm going to queue.


Takashi

-- 8< --
From: Takashi Iwai <tiwai at suse.de>
Subject: [PATCH] ALSA: hda: Fix too short HDMI/DP chmap reporting

We got a regression report about the HD-audio HDMI chmap, where some
surround channels are reported as UNKNOWN.  The git bisection pointed
the culprit at the commit 9b3dc8aa3fb1 ("ALSA: hda - Register chmap
obj as priv data instead of codec").  The story behind scene is like
this:

- While moving the code out of the legacy HDA to the HDA common place,
  the patch modifies the code to obtain the chmap array indirectly in
  a byte array, and it expands it to kctl value array.
- At the latter operation, the size of the array is wrongly passed by
  sizeof() to the pointer.
- It can be 4 on 32bit arch, thus too short for 6+ channels.
  (And that's the reason why it didn't hit other persons; it's 8 on
  64bit arch, thus it's usually enough.)

The code was further changed meanwhile, but the problem persisted.
Let's fix it by correctly evaluating the array size.

Fixes: 9b3dc8aa3fb1 ("ALSA: hda - Register chmap obj as priv data instead of codec")
Reported-by: VDR User <user.vdr at gmail.com>
Cc: <stable at vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/hda/hdmi_chmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/hda/hdmi_chmap.c b/sound/hda/hdmi_chmap.c
index 81acc20c2535..f21633cd9b38 100644
--- a/sound/hda/hdmi_chmap.c
+++ b/sound/hda/hdmi_chmap.c
@@ -746,7 +746,7 @@ static int hdmi_chmap_ctl_get(struct snd_kcontrol *kcontrol,
 	memset(pcm_chmap, 0, sizeof(pcm_chmap));
 	chmap->ops.get_chmap(chmap->hdac, pcm_idx, pcm_chmap);
 
-	for (i = 0; i < sizeof(chmap); i++)
+	for (i = 0; i < ARRAY_SIZE(pcm_chmap); i++)
 		ucontrol->value.integer.value[i] = pcm_chmap[i];
 
 	return 0;
-- 
2.15.0