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plugin: dynamically update avail_min on slave

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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>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Andreas Pape 2016-12-19 12:37:50 +09:00 • committed by Takashi Iwai
parent 7570e5d775
commit 88e4ae27bb
1 changed files with 63 additions and 1 deletions
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64
src/pcm/pcm_plugin.c
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@ -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