ALSA: uapi: pcm: control the filling of the silence samples for drain

Introduce SNDRV_PCM_INFO_PERFECT_DRAIN and SNDRV_PCM_HW_PARAMS_NO_DRAIN_SILENCE
flags to fully control the filling of the silence samples in the drain ioctl.
Actually, the configurable silencing is going to be implemented in the user
space [1], but drivers (hardware) may not require this operation. Those flags
do the bidirectional setup for this operation:

1) driver may notify the presence of the perfect drain
2) user space may not require the filling of the silence samples to inhibit clicks

If we decide to move this operation to the kernel space in future, the
SNDRV_PCM_INFO_PERFECT_DRAIN flag may handle this situation without
double "silence" processing (user + kernel space).

The ALSA API should be universal, so forcing the behaviour (modifying of
the ring buffer with any samples) for the drain operation is not ideal.

[1] https://lore.kernel.org/alsa-devel/20230502115010.986325-1-perex@perex.cz/

[ fixed a typo in comment by tiwai ]

Signed-off-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20230502115536.986900-1-perex@perex.cz
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
index 0aa955aa82463a63872a037dbd6ef7d3f08dfec1..6322823b527093fde10491620fbb471482686d80 100644 (file)
--- a/include/uapi/sound/asound.h
+++ b/include/uapi/sound/asound.h
@@ -274,6 +274,7 @@ typedef int __bitwise snd_pcm_subformat_t;
 #define SNDRV_PCM_INFO_DOUBLE          0x00000004      /* Double buffering needed for PCM start/stop */
 #define SNDRV_PCM_INFO_BATCH           0x00000010      /* double buffering */
 #define SNDRV_PCM_INFO_SYNC_APPLPTR    0x00000020      /* need the explicit sync of appl_ptr update */
+#define SNDRV_PCM_INFO_PERFECT_DRAIN   0x00000040      /* silencing at the end of stream is not required */
 #define SNDRV_PCM_INFO_INTERLEAVED     0x00000100      /* channels are interleaved */
 #define SNDRV_PCM_INFO_NONINTERLEAVED  0x00000200      /* channels are not interleaved */
 #define SNDRV_PCM_INFO_COMPLEX         0x00000400      /* complex frame organization (mmap only) */
@@ -383,6 +384,9 @@ 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)  /* suppress drain with the filling
+                                                        * of the silence samples
+                                                        */
 
 struct snd_interval {
        unsigned int min, max;