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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>
This commit is contained in:
Pierre-Louis Bossart 2012-09-21 18:39:05 -05:00 committed by Takashi Iwai
parent cf55e90451
commit 172d3b2096
1 changed files with 16 additions and 20 deletions
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36
sound/pci/hda/hda_intel.c
View File

@ -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;
}