Re: [PATCH] dma: pl330: Add support for DMA_PAUSE command

[Lars-Peter Clausen]

On 05/15/2014 02:01 PM, Tushar Behera wrote:
> On 14 May 2014 17:54, Lars-Peter Clausen <lars@xxxxxxxxxx> wrote:
> > On 05/14/2014 02:07 PM, Tushar Behera wrote:
> > > On 14 May 2014 17:29, Jassi Brar <jassisinghbrar@xxxxxxxxx> wrote:
> > > > On Wed, May 14, 2014 at 8:53 AM, Tushar Behera <tushar.behera@xxxxxxxxxx>
> > > > wrote:
> > > > > While playing back audio, pmc_dmaengine requests the DMA channel to
> > > > > stop DMA transmission through DMA_PAUSE command.
> > > > >
> > > > > Currently PL330 driver doesn't support DMA pause command, leaving
> > > > > the DMA state inconsistent when the system resumes. Instead, it would
> > > > > be better to terminate the DMA transfer during suspend and restart
> > > > > again during resume.
> > > > >
> > > > > Tested with audio playback across a suspend-resume cycle.
> > > > What is pmc_dmaengine? How does DMA_PAUSE help, when there is no
> > > > DMA_RESUME?
> > >
> > > Sorry, it is a typo.
> > >
> > > sound/core/pcm_dmaengine.c:snd_dmaengine_pcm_trigger() -->
> > > dmaengine_pause() is called during system suspend.
> >
> >
> > It is only called if the DMA driver has support for pausing and resuming DMA
> > transfers. Or at least that is the intention.
> >
> > - Lars
>
> During suspend, snd_dmaengine_pcm_trigger():SNDRV_PCM_TRIGGER_SUSPEND
> is called which unconditionally calls dmaengine_pause(). Should we
> update snd_dmaengine_pcm_trigger() to check for DMA pause/resume
> support and call dmaengine_pause() or dmaengine_terminate_all()
> accordingly?

As far as I understand it we do not have to do anything for TRIGGER_SUSPEND 
if we do not set the SNDRV_PCM_INFO_RESUME flag. It looks like 
TRIGGER_SUSPEND is called unconditionally during suspend. But since the 
error code is ignored it should be fine if we just call dmaengine_pause() 
and that return -ENOSYS or similar.

Are you seeing an actual issue that you are trying to fix with your patch?

- Lars

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