ALSA: cmipci: work around invalid PCM pointer

commit 1c583063a5c769fe2ec604752e383972c69e6d9b 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>

diff --git a/sound/pci/cmipci.c b/sound/pci/cmipci.c
index ddcd4a9fd7e69f1cf63fcbc0d79adc8868c4237a..78c8736638d3173b8b991ab4a7bab4d79aed3db0 100644 (file)
--- a/sound/pci/cmipci.c
+++ b/sound/pci/cmipci.c
@@ -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;