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pcm:plugin: Fix sound capture via MMAP access

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Distorted sound is heard if the capture device of an ioplug plugin is used,
which is accessed through any ALSA plugin (like copy, linear, ...) via MMAP access.
E.g. aplay -> loop -> copy -> arecord -M -> aplay -> hw:0
As mentioned in the ALSA API (see pcm/pcm.c:942):
The function #snd_pcm_avail_update() have to be called
before any mmap begin+commit operation.

Signed-off-by: Timo Wischer <twischer@de.adit-jv.com>
Signed-off-by: Mounesh Sutar <sutar.mounesh@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Timo Wischer 2017-04-04 12:00:18 +05:30 • committed by Takashi Iwai
parent ad6957c618
commit cb6e96bce1
1 changed files with 8 additions and 1 deletions
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9
src/pcm/pcm_plugin.c
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@ -490,7 +490,14 @@ static snd_pcm_sframes_t snd_pcm_plugin_avail_update(snd_pcm_t *pcm)
snd_pcm_uframes_t slave_offset;
snd_pcm_uframes_t slave_frames = ULONG_MAX;
snd_pcm_sframes_t result;
/* As mentioned in the ALSA API (see pcm/pcm.c:942):
* The function #snd_pcm_avail_update()
* have to be called before any mmap begin+commit operation.
* Otherwise the snd_pcm_areas_copy will not called a second time.
* But this is needed, if the ring buffer wrap is reached and
* there is more data available.
*/
slave_size = snd_pcm_avail_update(slave);
result = snd_pcm_mmap_begin(slave, &slave_areas, &slave_offset, &slave_frames);
if (result < 0) {
err = result;