Re: [PATCH v6 9/9] ALSA: virtio: introduce device suspend/resume support

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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?


--
Anton Yakovlev
Senior Software Engineer

OpenSynergy GmbH
Rotherstr. 20, 10245 Berlin

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