On Tue, 02 Mar 2021 07:29:20 +0100, Anton Yakovlev wrote:
On 28.02.2021 13:05, Takashi Iwai wrote:
On Sat, 27 Feb 2021 09:59:56 +0100, Anton Yakovlev wrote:
[snip]
--- a/sound/virtio/virtio_pcm.c +++ b/sound/virtio/virtio_pcm.c @@ -109,6 +109,7 @@ static int virtsnd_pcm_build_hw(struct virtio_pcm_substream *vss, SNDRV_PCM_INFO_BATCH | SNDRV_PCM_INFO_BLOCK_TRANSFER | SNDRV_PCM_INFO_INTERLEAVED |
SNDRV_PCM_INFO_RESUME | SNDRV_PCM_INFO_PAUSE;Actually you don't need to set SNDRV_PCM_INFO_RESUME. This flag means that the driver supports the full resume procedure, which isn't often the case; with this, the driver is supposed to resume the stream exactly from the suspended position.
Most drivers don't set this but implement only the suspend-stop action. Then the application (or the sound backend) will re-setup the stream and restart accordingly.
I tried to resume driver without SNDRV_PCM_INFO_RESUME, and alsa-lib called only ops->prepare(). It makes sense for a typical hw, but we have "clean" unconfigured device on resume. And we must set hw parameters as a first step. It means, that code should be more or less the same. And maybe it's better to set SNDRV_PCM_INFO_RESUME, since it allows us to resume substream in any situation (regardless of application behavior). I can refactor code to only send requests from trigger(RESUME) path and not to call ops itself. It should make code more straitforward. What do you say?
How about calling hw_params(NULL) conditionally in the prepare? Doing the full stack work in the trigger callback is bad from the API design POV; in general the trigger callback is supposed to be as short as possible.
Takashi