On 02.03.2021 07:48, Takashi Iwai wrote:
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?
Then the question is that condition. When ops->prepare() is called, the substream is in SUSPENDED state or not? If not then we need to track this in some additional field (and it will make logic a little bit clumsy, since that field is needed to be carefully handled in other places).
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.
Yeah, but usually original subsystem design does not take into account para-virtualized devices, which usually have it's own slightly different reality. And we need to introduce some tricks.
Takashi