From: Andreas Pape apape@de.adit-jv.com

mmapped capture access on some plugins can fetch data from slave in the 'background'. A subsequent snd_pcm_wait waits for too long time to reach avail_min threshold again. Waiting too long leads to xruns on other devices waiting for the capture data. As a fix the avail_min on slave is recalculated dynamically.

V2: updated patch to fix within 80 characters per line

Signed-off-by: Andreas Pape apape@de.adit-jv.com Signed-off-by: Jiada Wang jiada_wang@mentor.com --- src/pcm/pcm_plugin.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 63 insertions(+), 1 deletion(-)

diff --git a/src/pcm/pcm_plugin.c b/src/pcm/pcm_plugin.c index e53c5bb..5b65ac3 100644 --- a/src/pcm/pcm_plugin.c +++ b/src/pcm/pcm_plugin.c @@ -535,6 +535,68 @@ static int snd_pcm_plugin_status(snd_pcm_t *pcm, snd_pcm_status_t * status) return 0; }

+static int snd_pcm_plugin_may_wait_for_avail_min(snd_pcm_t *pcm, + snd_pcm_uframes_t avail) +{ + if (pcm->stream == SND_PCM_STREAM_CAPTURE && + pcm->access != SND_PCM_ACCESS_RW_INTERLEAVED && + pcm->access != SND_PCM_ACCESS_RW_NONINTERLEAVED) { + /* mmap access on capture device already consumes data from + * slave in avail_update operation. Entering snd_pcm_wait after + * having already consumed some fragments leads to waiting for + * too long time, as slave will unnecessarily wait for avail_min + * condition reached again. To avoid unnecessary wait times we + * adapt the avail_min threshold on slave dynamically. Just + * modifying slave->avail_min as a shortcut and lightweight + * solution does not work for all slave plugin types and in + * addition it will not propagate the change through all + * downstream plugins, so we have to use the sw_params API. + * note: reading fragmental parts from slave will only happen + * in case + * a) the slave can provide contineous hw_ptr between periods + * b) avail_min does not match one slave_period + */ + snd_pcm_plugin_t *plugin = pcm->private_data; + snd_pcm_t *slave = plugin->gen.slave; + snd_pcm_uframes_t needed_slave_avail_min; + snd_pcm_sframes_t available; + + /* update, as it might have changed. This will also call + * avail_update on slave and also can return error + */ + available = snd_pcm_avail_update(pcm); + if (available < 0) + return 0; + + if (available >= pcm->avail_min) + /* don't wait at all. As we can't configure avail_min + * of slave to 0 return here + */ + return 0; + + needed_slave_avail_min = pcm->avail_min - available; + if (slave->avail_min != needed_slave_avail_min) { + snd_pcm_sw_params_t *swparams; + snd_pcm_sw_params_alloca(&swparams); + /* pray that changing sw_params while running is + * properly implemented in all downstream plugins... + * it's legal but not commonly used. + */ + snd_pcm_sw_params_current(slave, swparams); + /* snd_pcm_sw_params_set_avail_min() restricts setting + * to >= period size. This conflicts at least with our + * dshare patch which allows combining multiple periods + * or with slaves which return hw postions between + * periods -> set directly in sw_param structure + */ + swparams->avail_min = needed_slave_avail_min; + snd_pcm_sw_params(slave, swparams); + } + avail = available; + } + return snd_pcm_generic_may_wait_for_avail_min(pcm, avail); +} + const snd_pcm_fast_ops_t snd_pcm_plugin_fast_ops = { .status = snd_pcm_plugin_status, .state = snd_pcm_generic_state, @@ -564,7 +626,7 @@ const snd_pcm_fast_ops_t snd_pcm_plugin_fast_ops = { .poll_descriptors_count = snd_pcm_generic_poll_descriptors_count, .poll_descriptors = snd_pcm_generic_poll_descriptors, .poll_revents = snd_pcm_generic_poll_revents, - .may_wait_for_avail_min = snd_pcm_generic_may_wait_for_avail_min, + .may_wait_for_avail_min = snd_pcm_plugin_may_wait_for_avail_min, };

#endif