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ALSA: cmipci: work around invalid PCM pointer 

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>
Cc: <stable@kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Clemens Ladisch 2010-03-24 07:10:54 +01:00 committed by Takashi Iwai
parent fc8aa7b16a
commit 1c583063a5
1 changed files with 11 additions and 3 deletions
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14
sound/pci/cmipci.c
View File

@ -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;