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ALSA: cmipci: work around invalid PCM pointer

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commit 1c583063a5 upstream.

When the CMI8738 FRAME2 register is read, the chip sometimes (probably
when wrapping around) returns an invalid value that would be outside the
programmed DMA buffer. This leads to an inconsistent PCM pointer that is
likely to result in an underrun.

To work around this, read the register multiple times until we get a
valid value; the error state seems to be very short-lived.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Reported-and-tested-by: Matija Nalis <mnalis-alsadev@voyager.hr>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Clemens Ladisch
2010-03-24 07:10:54 +01:00
committed by Greg Kroah-Hartman
parent f09315f7cd
commit 7a1bd86e26
1 changed files with 11 additions and 3 deletions
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14
sound/pci/cmipci.c
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@@ -941,13 +941,21 @@ static snd_pcm_uframes_t snd_cmipci_pcm_pointer(struct cmipci *cm, struct cmipci
struct snd_pcm_substream *substream)
{
size_t ptr;
unsigned int reg;
unsigned int reg, rem, tries;
if (!rec->running)
return 0;
#if 1 // this seems better..
reg = rec->ch ? CM_REG_CH1_FRAME2 : CM_REG_CH0_FRAME2;
ptr = rec->dma_size - (snd_cmipci_read_w(cm, reg) + 1);
ptr >>= rec->shift;
for (tries = 0; tries < 3; tries++) {
rem = snd_cmipci_read_w(cm, reg);
if (rem < rec->dma_size)
goto ok;
}
printk(KERN_ERR "cmipci: invalid PCM pointer: %#x\n", rem);
return SNDRV_PCM_POS_XRUN;
ok:
ptr = (rec->dma_size - (rem + 1)) >> rec->shift;
#else
reg = rec->ch ? CM_REG_CH1_FRAME1 : CM_REG_CH0_FRAME1;
ptr = snd_cmipci_read(cm, reg) - rec->offset;