On 05/16/2014 07:49 AM, Takashi Iwai wrote:
At Thu, 15 May 2014 21:21:12 +0200,
Lars-Peter Clausen wrote:
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.
Well, TRIGGER_SUSPEND is issued by PCM core no matter whether
SNDRV_PCM_INFO_RESUME flag is set or not. The resume behavior depends
on the flag (SNDRV_PCM_TRIGGER_RESUME is issued if the flag is set,
otherwise the normal setup is done by alsa-lib at resume), but the
suspend is always triggered in the same way.
So, PCM core assumes that the driver stops the stream somehow by
SNDRV_PCM_TRIGGER_SUSPEND.
Ok, so we should call terminate_all() when we get a
SNDRV_PCM_TRIGGER_SUSPEND if the dmaengine driver does not support pauseing
the transfer. Thanks for the clarification.
On a related note it seems like it is still possible to get
PAUSE_PUSH/PAUSE_RELEASE events even if SNDRV_PCM_INFO_PAUSE is not set. Do
you have an idea what should be the right thing to do in such a case? Return
-ENOSYS?
- Lars
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