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authorTakashi Iwai <tiwai@suse.de>2006-09-30 23:27:19 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-10-01 00:39:19 -0700
commit9442e691e4aec85eba43ac60a3e77c77fd2e73a4 (patch)
tree51314e5fcf6c023788df67a130cb6e692e5df496 /sound
parent5c87579e65ee4f419b2369407f82326d38b5d2d8 (diff)
[PATCH] maximum latency tracking: ALSA support
Add maximum latency tracking to the ALSA subsystem for PCM playback. In ALSA, the playback application controls the buffer size and thus indirectly the period of latency that it can deal with. This patch uses 75% of the total available latency as threshold to announce to the latency subsystem; While 75% is a crude heuristic it's a quite reasonable one; the remaining 25% can be used for all driver processing for the next samples which is also proportional to the size of the buffer. With ogg123 a latency setting of about 4msec was seen (at 44Khz), while with the "play" command a much longer maximum tolerable latency was seen. Other, more multimedia oriented players as well as games, will have a lot smaller buffers to allow better synchronization and those will actually get into the latency domains where there is impact on the power management rules. Signed-off-by: Takashi Iwai <tiwai@suse.de> Signed-off-by: Arjan van de Ven <arjan@linux.intel.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'sound')
-rw-r--r--sound/core/pcm.c3
-rw-r--r--sound/core/pcm_native.c23
2 files changed, 25 insertions, 1 deletions
diff --git a/sound/core/pcm.c b/sound/core/pcm.c
index bf8f412988b..fbbbcd20c4c 100644
--- a/sound/core/pcm.c
+++ b/sound/core/pcm.c
@@ -629,6 +629,9 @@ int snd_pcm_new_stream(struct snd_pcm *pcm, int stream, int substream_count)
substream->number = idx;
substream->stream = stream;
sprintf(substream->name, "subdevice #%i", idx);
+ snprintf(substream->latency_id, sizeof(substream->latency_id),
+ "ALSA-PCM%d-%d%c%d", pcm->card->number, pcm->device,
+ (stream ? 'c' : 'p'), idx);
substream->buffer_bytes_max = UINT_MAX;
if (prev == NULL)
pstr->substream = substream;
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 0224c70414f..891d7140553 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -25,6 +25,7 @@
#include <linux/file.h>
#include <linux/slab.h>
#include <linux/time.h>
+#include <linux/latency.h>
#include <linux/uio.h>
#include <sound/core.h>
#include <sound/control.h>
@@ -347,11 +348,26 @@ out:
return err;
}
+static int period_to_usecs(struct snd_pcm_runtime *runtime)
+{
+ int usecs;
+
+ if (! runtime->rate)
+ return -1; /* invalid */
+
+ /* take 75% of period time as the deadline */
+ usecs = (750000 / runtime->rate) * runtime->period_size;
+ usecs += ((750000 % runtime->rate) * runtime->period_size) /
+ runtime->rate;
+
+ return usecs;
+}
+
static int snd_pcm_hw_params(struct snd_pcm_substream *substream,
struct snd_pcm_hw_params *params)
{
struct snd_pcm_runtime *runtime;
- int err;
+ int err, usecs;
unsigned int bits;
snd_pcm_uframes_t frames;
@@ -431,6 +447,10 @@ static int snd_pcm_hw_params(struct snd_pcm_substream *substream,
snd_pcm_timer_resolution_change(substream);
runtime->status->state = SNDRV_PCM_STATE_SETUP;
+
+ remove_acceptable_latency(substream->latency_id);
+ if ((usecs = period_to_usecs(runtime)) >= 0)
+ set_acceptable_latency(substream->latency_id, usecs);
return 0;
_error:
/* hardware might be unuseable from this time,
@@ -490,6 +510,7 @@ static int snd_pcm_hw_free(struct snd_pcm_substream *substream)
if (substream->ops->hw_free)
result = substream->ops->hw_free(substream);
runtime->status->state = SNDRV_PCM_STATE_OPEN;
+ remove_acceptable_latency(substream->latency_id);
return result;
}