From 1c583063a5c769fe2ec604752e383972c69e6d9b Mon Sep 17 00:00:00 2001 From: Clemens Ladisch Date: Wed, 24 Mar 2010 07:10:54 +0100 Subject: 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 Reported-and-tested-by: Matija Nalis Cc: Signed-off-by: Takashi Iwai --- sound/pci/cmipci.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/sound/pci/cmipci.c b/sound/pci/cmipci.c index 1ded64e05643..329968edca9b 100644 --- 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; -- cgit v1.2.3