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@metafoo.de wrote:
On 05/14/2014 02:07 PM, Tushar Behera wrote:
On 14 May 2014 17:29, Jassi Brar jassisinghbrar@gmail.com wrote:
On Wed, May 14, 2014 at 8:53 AM, Tushar Behera tushar.behera@linaro.org 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