On Tue, May 02, 2023 at 01:50:10PM +0200, Jaroslav Kysela wrote:
The application may not require to touch the sample stream
for the drain operation at all. Handle this situation
in alsa-lib.
i find this too vague.
This allows an application which uses an mmapped buffer to inform us
that it is handling the silence padding itself.
Signed-off-by: Jaroslav Kysela <perex@xxxxxxxx>
---
include/sound/uapi/asound.h | 3 +++
src/pcm/pcm.c | 32 ++++++++++++++++++++++++++++++++
src/pcm/pcm_hw.c | 3 ++-
src/pcm/pcm_local.h | 1 +
4 files changed, 38 insertions(+), 1 deletion(-)
diff --git a/include/sound/uapi/asound.h b/include/sound/uapi/asound.h
index 0b8834f2..f970179e 100644
--- a/include/sound/uapi/asound.h
+++ b/include/sound/uapi/asound.h
@@ -390,6 +390,9 @@ typedef int snd_pcm_hw_param_t;
#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_DRAIN_SILENCE (1<<3) /* supress drain with the filling
+ * of the silence samples
+ */
"suppress automatic silence fill when draining playback"
--- a/src/pcm/pcm.c
+++ b/src/pcm/pcm.c
@@ -4958,6 +4958,38 @@ int snd_pcm_hw_params_get_period_wakeup(snd_pcm_t *pcm, snd_pcm_hw_params_t *par
return 0;
}
+/**
+ * \brief Restrict a configuration space to allow the drain with the
filling of silence samples
there is no way i'd understand what this means. in fact, i'm having a
hard time even though i more or less know it already.
+ * \param pcm PCM handle
+ * \param params Configuration space
+ * \param val 0 = disable, 1 = enable (default) drain with the filling of silence samples
"padding the playback buffer with silence when drain() is invoked"
+ * \return 0 otherwise a negative error code
add description:
"When disabled, the application must ensure that enough samples are
silenced, as most hardware will read beyond the application pointer when
drain() is invoked."
+/**
+ * \brief Extract drain with the filling of silence samples from a configuration space
this is also kinda incomprehensible.
+ * \param pcm PCM handle
+ * \param params Configuration space
+ * \param val 0 = disable, 1 = enable
as this returns the status quo, this should be disabled/enabled.
+ * \return 0 otherwise a negative error code
there is no "otherwise" here.
+ */
+int snd_pcm_hw_params_get_drain_silence(snd_pcm_t *pcm, snd_pcm_hw_params_t *params, unsigned int *val)
+{
+ assert(pcm && params && val);
+ *val = params->flags & SND_PCM_HW_PARAMS_NO_DRAIN_SILENCE ? 0 : 1;
i know i'm paranoid, but i'd put extra parens around the condition.
+ return 0;
+}
+
--- a/src/pcm/pcm_hw.c
+++ b/src/pcm/pcm_hw.c
@@ -399,7 +399,8 @@ static int snd_pcm_hw_hw_params(snd_pcm_t *pcm, snd_pcm_hw_params_t * params)
- hw->perfect_drain = !!(params->info & SND_PCM_INFO_PERFECT_DRAIN);
+ hw->perfect_drain = !!(params->info & SND_PCM_INFO_PERFECT_DRAIN) ||
+ !!(params->flags & SND_PCM_HW_PARAMS_NO_DRAIN_SILENCE);
pedantically, you can remove the double negations as this point.
regards
