During the card registration, transactions on the SoundWire bus can be initiated. If the ALSA card is registered after the bus suspends, timeouts can be seen while reading/writing codec registers. This is extremely easy to reproduce in driver bind/unbind tests.
In an initial experiment, the ASoC soc-component.c code was modified to initiate a pm_runtime resume on a component probe. The results showed this was too invasive. Instead this patch suggests resuming the SoundWire component only.
Because of the parent-child hierarchy enforced by the pm_runtime framework, it can be argued that the codec component probe should be enough to resume all necessary devices, and indeed the same resume will be applied to SoundWire codecs used on Intel platforms.
Calling pm_runtime_resume() on both the Intel and codec sides has the benefit of resuming the bus without assuming any order during the card registration. The first component on a dailink to be probed will resume the bus. In addition, if a codec driver did not implement this transition, the Intel component would still resume the bus and avoid timeouts on card registration.
BugLink: https://github.com/thesofproject/linux/issues/3651 Reviewed-by: Rander Wang rander.wang@intel.com Reviewed-by: Ranjani Sridharan ranjani.sridharan@linux.intel.com Reviewed-by: Bard Liao yung-chuan.liao@linux.intel.com Reviewed-by: Péter Ujfalusi peter.ujfalusi@linux.intel.com Signed-off-by: Pierre-Louis Bossart pierre-louis.bossart@linux.intel.com --- drivers/soundwire/intel.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)
diff --git a/drivers/soundwire/intel.c b/drivers/soundwire/intel.c index 2e7c27d303b42..c907bab12ee33 100644 --- a/drivers/soundwire/intel.c +++ b/drivers/soundwire/intel.c @@ -1051,6 +1051,23 @@ static int intel_trigger(struct snd_pcm_substream *substream, int cmd, struct sn return ret; }
+static int intel_component_probe(struct snd_soc_component *component) +{ + int ret; + + /* + * make sure the device is pm_runtime_active before initiating + * bus transactions during the card registration. + * We use pm_runtime_resume() here, without taking a reference + * and releasing it immediately. + */ + ret = pm_runtime_resume(component->dev); + if (ret < 0 && ret != -EACCES) + return ret; + + return 0; +} + static int intel_component_dais_suspend(struct snd_soc_component *component) { struct snd_soc_dai *dai; @@ -1106,6 +1123,7 @@ static const struct snd_soc_dai_ops intel_pcm_dai_ops = {
static const struct snd_soc_component_driver dai_component = { .name = "soundwire", + .probe = intel_component_probe, .suspend = intel_component_dais_suspend };