ALSA: cmipci: work around invalid PCM pointer (1c583063) · Commits · 戴 / test

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>

sound/pci/cmipci.c

+11 −3

Original line number	Diff line number	Diff line
		@@ -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;

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