On 02.03.2021 10:11, Takashi Iwai wrote:
On Tue, 02 Mar 2021 09:09:33 +0100, Anton Yakovlev wrote:
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).
Yes, you'd need to have a suspend/resume PM callback in the driver that flips the internal flag to invalidate the hw_parmas, and in the prepare callback, just call hw_params(NULL) if that flag is set.
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.
The hardware drivers do a lot of more things in either suspend/resume PM callbacks or prepare callback for re-setup of the hardware. We can follow the similar pattern. Heavy-lifting works in the trigger callbacks is really something to avoid.
Ok, I redone this part and now the driver sets parameters for the device in ops->prepare() if the substream was suspended. And everything works fine. Thanks! I will send a new patch set soon.
Takashi