30.01.2020 19:08, Dmitry Osipenko пишет:

30.01.2020 17:09, Jon Hunter пишет:

quoted

On 30/01/2020 04:38, Dmitry Osipenko wrote:

quoted

It is enough to check whether hardware is busy on suspend and to reset
it across of suspend-resume because channel's configuration is fully
re-programmed on each DMA transaction anyways and because save-restore
of an active channel won't end up well without pausing transfer prior to
saving of the state (note that all channels shall be idling at the time of
suspend, so save-restore is not needed at all).

I guess if we ever wanted to support SNDRV_PCM_INFO_PAUSE for audio and
support the pause callback, then saving and restoring the channels could
be needed. Right now I believe that it will just terminate_all transfers
for audio on entering suspend. Any value in keeping this?

Indeed, looks like [1] pauses DMA during suspend if SNDRV_PCM_INFO_PAUSE
is supported.

[1]
https://elixir.bootlin.com/linux/v5.5/source/sound/core/pcm_dmaengine.c#L199

So we'll need to save-restore context only if DMA is in a paused state
during suspend, I'll adjust this patch to do that and will see if
enabling SNDRV_PCM_INFO_PAUSE works.

I started to look at it and found that the .device_pause() hook isn't
implemented by the driver. So, it's fine to remove the context's
save-restore for now.

Jon, what about to keep this patch as-is? Later on I'll take a look at
implementing the proper pausing functionality and try to cleanup code a
bit further (remove the free list usage, etc).