Re: sound skipping regression introduced in 2.6.30-rc8

From: Takashi Iwai
Date: Mon Jun 15 2009 - 05:58:26 EST


At Mon, 15 Jun 2009 11:48:43 +0200,
I wrote:
>
> At Mon, 15 Jun 2009 02:25:47 -0700 (PDT),
> David Miller wrote:
> >
> > From: Takashi Iwai <tiwai@xxxxxxx>
> > Date: Mon, 15 Jun 2009 10:39:50 +0200
> >
> > > If that patch also doesn't work, we need to track the position update
> > > sequence in more details.
> > > The patch below will dump the each position update (CAUTION: it can be
> > > long logs!). Please apply it instead of the previous one, run with
> > > xrun_debug=5 on 2.6.31 (or xrun_debug=1 on 2.6.30), and give the
> > > outputs around a skip occurs.
> >
> > The patch doesn't work.
> >
> > I put up a debugging log at:
> >
> > http://vger.kernel.org/~davem/asound.log
> >
> > there is a "PCM: hw_ptr skipping! ..." message near the end.
>
> Thanks! I see the problem now. It's a race in the update of the
> current buffer position. The counter was reset to the full fragment
> size, but its index still points the previous position. So, the
> driver was confused and put the position back.
>
> The below is a revised patch. It has an additional sanity check.
> Please give it a try.

Damn, that was buggy again. The fixed version is below.


Takashi

---
diff --git a/sound/pci/intel8x0.c b/sound/pci/intel8x0.c
index 173bebf..8aa5687 100644
--- a/sound/pci/intel8x0.c
+++ b/sound/pci/intel8x0.c
@@ -356,8 +356,6 @@ struct ichdev {
unsigned int position;
unsigned int pos_shift;
unsigned int last_pos;
- unsigned long last_pos_jiffies;
- unsigned int jiffy_to_bytes;
int frags;
int lvi;
int lvi_frag;
@@ -844,7 +842,6 @@ static int snd_intel8x0_pcm_trigger(struct snd_pcm_substream *substream, int cmd
case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
val = ICH_IOCE | ICH_STARTBM;
ichdev->last_pos = ichdev->position;
- ichdev->last_pos_jiffies = jiffies;
break;
case SNDRV_PCM_TRIGGER_SUSPEND:
ichdev->suspended = 1;
@@ -1048,7 +1045,6 @@ static int snd_intel8x0_pcm_prepare(struct snd_pcm_substream *substream)
ichdev->pos_shift = (runtime->sample_bits > 16) ? 2 : 1;
}
snd_intel8x0_setup_periods(chip, ichdev);
- ichdev->jiffy_to_bytes = (runtime->rate * 4 * ichdev->pos_shift) / HZ;
return 0;
}

@@ -1073,19 +1069,23 @@ static snd_pcm_uframes_t snd_intel8x0_pcm_pointer(struct snd_pcm_substream *subs
ptr1 == igetword(chip, ichdev->reg_offset + ichdev->roff_picb))
break;
} while (timeout--);
+ ptr = ichdev->last_pos;
if (ptr1 != 0) {
ptr1 <<= ichdev->pos_shift;
ptr = ichdev->fragsize1 - ptr1;
ptr += position;
- ichdev->last_pos = ptr;
- ichdev->last_pos_jiffies = jiffies;
- } else {
- ptr1 = jiffies - ichdev->last_pos_jiffies;
- if (ptr1)
- ptr1 -= 1;
- ptr = ichdev->last_pos + ptr1 * ichdev->jiffy_to_bytes;
- ptr %= ichdev->size;
+ if (ptr < ichdev->last_pos) {
+ unsigned int pos_base, last_base;
+ pos_base = position / ichdev->fragsize1;
+ last_base = ichdev->last_pos / ichdev->fragsize1;
+ /* another sanity check; ptr1 can go back to full
+ * before the base position is updated
+ */
+ if (pos_base == last_base)
+ ptr = ichdev->last_pos;
+ }
}
+ ichdev->last_pos = ptr;
spin_unlock(&chip->reg_lock);
if (ptr >= ichdev->size)
return 0;
--
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