ALSA: hda - Add workaround for CMI8888 snoop behavior

CMI8888 shows the stuttering playback when the snooping is disabled
on the audio buffer.  Meanwhile, we've got reports that CORB/RIRB
doesn't work in the snooped mode.  So, as a compromise, disable the
snoop only for CORB/RIRB and enable the snoop for the stream buffers.

The resultant patch became a bit ugly, unfortunately, but we still can
live with it.
Reported-and-tested-by: Geoffrey McRae <geoff@spacevs.com>
Cc: <stable@vger.kernel.org> # 3.17+
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/hda/hda_intel.c

@@ -374,6 +374,8 @@ static void __mark_pages_wc(struct azx *chip, struct snd_dma_buffer *dmab, bool
 #ifdef CONFIG_SND_DMA_SGBUF
 	if (dmab->dev.type == SNDRV_DMA_TYPE_DEV_SG) {
 		struct snd_sg_buf *sgbuf = dmab->private_data;
+		if (chip->driver_type == AZX_DRIVER_CMEDIA)
+			return; /* deal with only CORB/RIRB buffers */
 		if (on)
 			set_pages_array_wc(sgbuf->page_table, sgbuf->pages);
 		else
@@ -1769,7 +1771,7 @@ static void pcm_mmap_prepare(struct snd_pcm_substream *substream,
 #ifdef CONFIG_X86
 	struct azx_pcm *apcm = snd_pcm_substream_chip(substream);
 	struct azx *chip = apcm->chip;
-	if (!azx_snoop(chip))
+	if (!azx_snoop(chip) && chip->driver_type != AZX_DRIVER_CMEDIA)
 		area->vm_page_prot = pgprot_writecombine(area->vm_page_prot);
 #endif
 }