ALSA: intel8x0: Improve comments for VM optimization

The recently merged 228cf79376f1 looks a bit hackish while it is not.
The change was quite simple. In a virtualized environment the
patch unhacks old kludge introduced for old broken AC97 hardware.

This patch adds proper comment to "unkludge" code.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: Konstantin Ozerkov <kozerkov@parallels.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 7 insertions, 0 deletions

diff --git a/sound/pci/intel8x0.c b/sound/pci/intel8x0.c
index 29e312597f20..c3b9bd0e188e 100644
--- a/sound/pci/intel8x0.c
+++ b/sound/pci/intel8x0.c
@@ -1077,6 +1077,13 @@ static snd_pcm_uframes_t snd_intel8x0_pcm_pointer(struct snd_pcm_substream *subs
                 }
                 if (civ != igetbyte(chip, ichdev->reg_offset + ICH_REG_OFF_CIV))
                         continue;
+
+                /* IO read operation is very expensive inside virtual machine
+                 * as it is emulated. The probability that subsequent PICB read
+                 * will return different result is high enough to loop till
+                 * timeout here.
+                 * Same CIV is strict enough condition to be sure that PICB
+                 * is valid inside VM on emulated card. */
                 if (chip->inside_vm)
                         break;
                 if (ptr1 == igetword(chip, ichdev->reg_offset + ichdev->roff_picb))