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.
Takashi