From cb6e96bce1c43c26d9e12d031ed1ef027140b988 Mon Sep 17 00:00:00 2001 From: Timo Wischer Date: Tue, 4 Apr 2017 12:00:18 +0530 Subject: [PATCH] pcm:plugin: Fix sound capture via MMAP access 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 Signed-off-by: Mounesh Sutar Signed-off-by: Takashi Iwai --- src/pcm/pcm_plugin.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/src/pcm/pcm_plugin.c b/src/pcm/pcm_plugin.c index aaea2ab2..ec57f6e9 100644 --- a/src/pcm/pcm_plugin.c +++ b/src/pcm/pcm_plugin.c @@ -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; -- 2.11.0