The patch titled
maximum latency tracking: ALSA support
has been added to the -mm tree. Its filename is
maximum-latency-tracking-alsa-support.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: maximum latency tracking: ALSA support
From: Takashi Iwai <tiwai@xxxxxxx>
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@xxxxxxx>
Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
include/sound/pcm.h | 1 +
sound/core/pcm.c | 3 +++
sound/core/pcm_native.c | 23 ++++++++++++++++++++++-
3 files changed, 26 insertions(+), 1 deletion(-)
diff -puN include/sound/pcm.h~maximum-latency-tracking-alsa-support include/sound/pcm.h
--- a/include/sound/pcm.h~maximum-latency-tracking-alsa-support
+++ a/include/sound/pcm.h
@@ -347,6 +347,7 @@ struct snd_pcm_substream {
int number;
char name[32]; /* substream name */
int stream; /* stream (direction) */
+ char latency_id[20]; /* latency identifier */
size_t buffer_bytes_max; /* limit ring buffer size */
struct snd_dma_buffer dma_buffer;
unsigned int dma_buf_id;
diff -puN sound/core/pcm.c~maximum-latency-tracking-alsa-support sound/core/pcm.c
--- a/sound/core/pcm.c~maximum-latency-tracking-alsa-support
+++ a/sound/core/pcm.c
@@ -629,6 +629,9 @@ int snd_pcm_new_stream(struct snd_pcm *p
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 -puN sound/core/pcm_native.c~maximum-latency-tracking-alsa-support sound/core/pcm_native.c
--- a/sound/core/pcm_native.c~maximum-latency-tracking-alsa-support
+++ a/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_
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_pc
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;
}
_
Patches currently in -mm which might be from tiwai@xxxxxxx are
alsa-ac97-correct-some-mic-mixer-elements.patch
git-alsa.patch
git-geode.patch
maximum-latency-tracking-alsa-support.patch
-
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
