ALSA: intel8x0 - Fix PCM position craziness

The PCM pointer callback sometimes returns invalid positions and this
screws up the hw_ptr updater in PCM core.  Especially since now the
jiffies check is optional with xrun_debug, the invalid position is
handled as is, and causes serious sound skips, etc.

This patch simplifies the position-fix strategy in intel8x0 to be more
robust:
- just falls back to the last position if bogus position is detected
- another sanity check for the backward move of the position due to
  a race of register update and the base-index update

This patch is applicable also for 2.6.30.

Tested-by: David Miller <davem@davemloft.net>
Cc: <stable@kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 12 insertions, 12 deletions

diff --git a/sound/pci/intel8x0.c b/sound/pci/intel8x0.c
index 173bebf9f51d..8aa5687f392a 100644
--- a/sound/pci/intel8x0.c
+++ b/sound/pci/intel8x0.c
@@ -356,8 +356,6 @@ struct ichdev {
         unsigned int position;
         unsigned int pos_shift;
         unsigned int last_pos;
-        unsigned long last_pos_jiffies;
-        unsigned int jiffy_to_bytes;
         int frags;
         int lvi;
         int lvi_frag;
@@ -844,7 +842,6 @@ static int snd_intel8x0_pcm_trigger(struct snd_pcm_substream *substream, int cmd
         case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
                 val = ICH_IOCE | ICH_STARTBM;
                 ichdev->last_pos = ichdev->position;
-                ichdev->last_pos_jiffies = jiffies;
                 break;
         case SNDRV_PCM_TRIGGER_SUSPEND:
                 ichdev->suspended = 1;
@@ -1048,7 +1045,6 @@ static int snd_intel8x0_pcm_prepare(struct snd_pcm_substream *substream)
                         ichdev->pos_shift = (runtime->sample_bits > 16) ? 2 : 1;
         }
         snd_intel8x0_setup_periods(chip, ichdev);
-        ichdev->jiffy_to_bytes = (runtime->rate * 4 * ichdev->pos_shift) / HZ;
         return 0;
 }
 
@@ -1073,19 +1069,23 @@ static snd_pcm_uframes_t snd_intel8x0_pcm_pointer(struct snd_pcm_substream *subs
                     ptr1 == igetword(chip, ichdev->reg_offset + ichdev->roff_picb))
                         break;
         } while (timeout--);
+        ptr = ichdev->last_pos;
         if (ptr1 != 0) {
                 ptr1 <<= ichdev->pos_shift;
                 ptr = ichdev->fragsize1 - ptr1;
                 ptr += position;
-                ichdev->last_pos = ptr;
-                ichdev->last_pos_jiffies = jiffies;
-        } else {
-                ptr1 = jiffies - ichdev->last_pos_jiffies;
-                if (ptr1)
-                        ptr1 -= 1;
-                ptr = ichdev->last_pos + ptr1 * ichdev->jiffy_to_bytes;
-                ptr %= ichdev->size;
+                if (ptr < ichdev->last_pos) {
+                        unsigned int pos_base, last_base;
+                        pos_base = position / ichdev->fragsize1;
+                        last_base = ichdev->last_pos / ichdev->fragsize1;
+                        /* another sanity check; ptr1 can go back to full
+                         * before the base position is updated
+                         */
+                        if (pos_base == last_base)
+                                ptr = ichdev->last_pos;
+                }
         }
+        ichdev->last_pos = ptr;
         spin_unlock(&chip->reg_lock);
         if (ptr >= ichdev->size)
                 return 0;