On 6/19/17 3:44 AM, Takashi Iwai wrote:
On Mon, 19 Jun 2017 08:22:37 +0200,
Subhransu S. Prusty wrote:
From: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
Add new hw_params flag to explicitly tell driver that rewinds will never
be used. This can be used by low-level driver to optimize DMA operations
and reduce power consumption. Use this flag only when data written in
ring buffer will never be invalidated, e.g. any update of appl_ptr is
final.
Note that the update of appl_ptr include both a read/write data
operation as well as snd_pcm_forward() whose behavior is not modified.
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
Signed-off-by: Ramesh Babu <ramesh.babu@xxxxxxxxx>
Signed-off-by: Subhransu S. Prusty <subhransu.s.prusty@xxxxxxxxx>
---
v2 -> v3
return error for rewind operation if no_rewinds set.
Now I'm thinking whether this change is really needed or in the right
direction. I suppose that the driver would change the behavior
depending on the flag of this flag. But then how can application know
that it should not rewind on a certain device and set the flag?
The application (which is in most cases an audio server) *knows* if it
requires rewinds or not. It's part of its design, with rewinds typically
disabled if period interrupts are required. It's been that way for a
number of years now. The use of rewinds is typically associated with the
combination of a large buffer and no interrupts (having either of the
two would not require rewinds).
So the idea is that the application makes a statement that rewinds will
not be used, and the low-level driver makes use of the information to
enable whatever optimizations are available at the hardware level.
Exposing more information to userspace would quickly lead to a confusing
decision-making and would require more than just a flag.
We may, instead, let the driver behaving in the deep buffer mode as
default (or turned on/off via the kcontrol). Then you can simply
return an error for the negative appl_ptr change in ack callback --
which effectively disables the rewind.
thanks,
Takashi
include/sound/pcm.h | 1 +
include/uapi/sound/asound.h | 1 +
sound/core/pcm_native.c | 8 ++++++++
3 files changed, 10 insertions(+)
diff --git a/include/sound/pcm.h b/include/sound/pcm.h
index 79fedf517070..c1e2b87cd409 100644
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -368,6 +368,7 @@ struct snd_pcm_runtime {
unsigned int rate_num;
unsigned int rate_den;
unsigned int no_period_wakeup: 1;
+ unsigned int no_rewinds:1;
/* -- SW params -- */
int tstamp_mode; /* mmap timestamp is updated */
diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
index fd41697cb4d3..c697ff90450d 100644
--- a/include/uapi/sound/asound.h
+++ b/include/uapi/sound/asound.h
@@ -365,6 +365,7 @@ struct snd_pcm_info {
#define SNDRV_PCM_HW_PARAMS_NORESAMPLE (1<<0) /* avoid rate resampling */
#define SNDRV_PCM_HW_PARAMS_EXPORT_BUFFER (1<<1) /* export buffer */
#define SNDRV_PCM_HW_PARAMS_NO_PERIOD_WAKEUP (1<<2) /* disable period wakeups */
+#define SNDRV_PCM_HW_PARAMS_NO_REWINDS (1<<3) /* disable rewinds */
struct snd_interval {
unsigned int min, max;
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index bf5d0f2acfb9..6769f4751fa0 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -554,6 +554,8 @@ static int snd_pcm_hw_params(struct snd_pcm_substream *substream,
runtime->no_period_wakeup =
(params->info & SNDRV_PCM_INFO_NO_PERIOD_WAKEUP) &&
(params->flags & SNDRV_PCM_HW_PARAMS_NO_PERIOD_WAKEUP);
+ runtime->no_rewinds =
+ (params->flags & SNDRV_PCM_HW_PARAMS_NO_REWINDS) ? 1 : 0;
bits = snd_pcm_format_physical_width(runtime->format);
runtime->sample_bits = bits;
@@ -2521,6 +2523,9 @@ static snd_pcm_sframes_t snd_pcm_playback_rewind(struct snd_pcm_substream *subst
if (frames == 0)
return 0;
+ if (runtime->no_rewinds)
+ return -ENODEV;
+
snd_pcm_stream_lock_irq(substream);
ret = do_pcm_hwsync(substream);
if (!ret)
@@ -2539,6 +2544,9 @@ static snd_pcm_sframes_t snd_pcm_capture_rewind(struct snd_pcm_substream *substr
if (frames == 0)
return 0;
+ if (runtime->no_rewinds)
+ return -ENODEV;
+
snd_pcm_stream_lock_irq(substream);
ret = do_pcm_hwsync(substream);
if (!ret)
--
1.9.1
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