Messages in this thread | | | Date | Mon, 19 May 2014 10:43:33 +0200 | From | Lars-Peter Clausen <> | Subject | Re: [alsa-devel] [PATCH] dma: pl330: Add support for DMA_PAUSE command |
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On 05/19/2014 10:37 AM, Takashi Iwai wrote: > At Fri, 16 May 2014 12:51:51 +0200, > Lars-Peter Clausen wrote: >> >> 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? > > That's weird. We have already a check in snd_pcm_pre_pause() in > pcm_native.c to filter only for substreams with SNDRV_PCM_INFO_PAUSE > flag. > > Could you check in which code path it is triggered?
Uhm, yes, I was only looking at the code, but couldn't find the check that makes sure that the PAUSE_PUSH/PAUSE_RELEASE events are only triggered if SNDRV_PCM_INFO_PAUSE is set. Looks like I need a pair of glasses.
Thanks and sorry for the noise, - Lars
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