[alsa-devel] multi-channel playback regression

[Takashi Iwai]

At Thu, 23 Jul 2009 15:56:20 +0800,
Wu Fengguang wrote:
> 
> On Thu, Jul 23, 2009 at 03:30:54PM +0800, Takashi Iwai wrote:
> > At Thu, 23 Jul 2009 15:22:53 +0800,
> > Wu Fengguang wrote:
> > > 
> > > On Thu, Jul 23, 2009 at 03:01:21PM +0800, Takashi Iwai wrote:
> > > > At Thu, 23 Jul 2009 14:53:45 +0800,
> > > > Wu Fengguang wrote:
> > > > > 
> > > > > Hi Takashi,
> > > > > 
> > > > > When doing multi-channel playback tests on IbexPeak, I found that the
> > > > > following patch makes the playback enter an infinite loop, repeatedly
> > > > > playing a range of ~0.5s audio content. (Seems that some buffer
> > > > > pointer can never advance.)
> > > > 
> > > > Could you set 1 to /proc/asound/card0/pcm0p/xrun_debug and give the
> > > > messages?  Also, please show /proc/.../pcm0p/sub0/hw_params, too.
> > > > 
> > > > The change affects only the code path for the problematic hardware
> > > > that reports wrong DMA position.  So, if this change regresses, it
> > > > means that the device has been already problematic from the
> > > > beginning...
> > > 
> > > I caught some messages:
> > 
> > Is this with the patched (as is on sound git tree) kernel?
> 
> Yes, it's unmodified latest git tree.
> 
> > What if changing from #if 1 to #if 0?
> 
> This makes 8-channel playback work again.

Mea culpa, that was a bug in my code :<

The patch below fixes the issue.  Already merged on GIT trees and
snapshot tarballs.

Sorry for inconvenience!


Takashi

===
From 947ca210f1df7656e19890832cb71fc3bdd88707 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai at suse.de>
Date: Thu, 23 Jul 2009 16:21:08 +0200
Subject: [PATCH] ALSA: pcm - Fix hwptr buffer-size overlap bug

The fix 79452f0a28aa5a40522c487b42a5fc423647ad98 introduced another
bug due to the missing offset for the overlapped hwptr.
When the hwptr goes back to zero, the delta value has to be corrected
with the buffer size.  Otherwise this causes looping sounds.

Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/core/pcm_lib.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index d315f72..72cfd47 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -256,7 +256,7 @@ static int snd_pcm_update_hw_ptr_interrupt(struct snd_pcm_substream *substream)
 			delta = new_hw_ptr - hw_ptr_interrupt;
 	}
 	if (delta < 0) {
-		if (runtime->periods == 1)
+		if (runtime->periods == 1 || new_hw_ptr < old_hw_ptr)
 			delta += runtime->buffer_size;
 		if (delta < 0) {
 			hw_ptr_error(substream, 
-- 
1.6.3.3