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Commit 172d3b20 authored by Pierre-Louis Bossart's avatar Pierre-Louis Bossart Committed by Takashi Iwai
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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: default avatarPierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent cf55e904

sound/pci/hda/hda_intel.c

+16 −20
Original line number Diff line number Diff line
@@ -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);

	}



	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;
@@ -2045,7 +2043,6 @@ 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)
@@ -2054,7 +2051,6 @@ static int azx_pcm_trigger(struct snd_pcm_substream *substream, int cmd) 
	else

		azx_writel(chip, SSYNC, azx_readl(chip, SSYNC) & ~sbits);

	spin_unlock(&chip->reg_lock);

	}

	return 0;

}