ALSA: hda - force use of SSYNC bits

SSYNC bits are typically used to start multiple
streams synchronously. It makes sense to use them
for a single stream for a more predictable startup
sequence. The transfers only start once the DMA and
FIFOs are ready. This results in a better correlation
between timestamps and number of samples played.

Credits to Kar Leong Wang for suggesting this
improvement.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 16 insertions, 20 deletions

diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
index 207d0a20f31..f4070a4f39f 100644
--- a/sound/pci/hda/hda_intel.c
+++ b/sound/pci/hda/hda_intel.c
@@ -1986,14 +1986,14 @@ static int azx_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
         }
 
         spin_lock(&chip->reg_lock);
-        if (nsync > 1) {
-                /* first, set SYNC bits of corresponding streams */
-                if (chip->driver_caps & AZX_DCAPS_OLD_SSYNC)
-                        azx_writel(chip, OLD_SSYNC,
-                                   azx_readl(chip, OLD_SSYNC) | sbits);
-                else
-                        azx_writel(chip, SSYNC, azx_readl(chip, SSYNC) | sbits);
-        }
+
+        /* first, set SYNC bits of corresponding streams */
+        if (chip->driver_caps & AZX_DCAPS_OLD_SSYNC)
+                azx_writel(chip, OLD_SSYNC,
+                        azx_readl(chip, OLD_SSYNC) | sbits);
+        else
+                azx_writel(chip, SSYNC, azx_readl(chip, SSYNC) | sbits);
+
         snd_pcm_group_for_each_entry(s, substream) {
                 if (s->pcm->card != substream->pcm->card)
                         continue;
@@ -2011,8 +2011,6 @@ static int azx_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
         }
         spin_unlock(&chip->reg_lock);
         if (start) {
-                if (nsync == 1)
-                        return 0;
                 /* wait until all FIFOs get ready */
                 for (timeout = 5000; timeout; timeout--) {
                         nwait = 0;
@@ -2045,16 +2043,14 @@ static int azx_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
                         cpu_relax();
                 }
         }
-        if (nsync > 1) {
-                spin_lock(&chip->reg_lock);
-                /* reset SYNC bits */
-                if (chip->driver_caps & AZX_DCAPS_OLD_SSYNC)
-                        azx_writel(chip, OLD_SSYNC,
-                                   azx_readl(chip, OLD_SSYNC) & ~sbits);
-                else
-                        azx_writel(chip, SSYNC, azx_readl(chip, SSYNC) & ~sbits);
-                spin_unlock(&chip->reg_lock);
-        }
+        spin_lock(&chip->reg_lock);
+        /* reset SYNC bits */
+        if (chip->driver_caps & AZX_DCAPS_OLD_SSYNC)
+                azx_writel(chip, OLD_SSYNC,
+                        azx_readl(chip, OLD_SSYNC) & ~sbits);
+        else
+                azx_writel(chip, SSYNC, azx_readl(chip, SSYNC) & ~sbits);
+        spin_unlock(&chip->reg_lock);
         return 0;
 }