[alsa-devel] ASoC: tegra: Does the PCM_TRIGGER_{PAUSE, RESUME} emulation really work?

Lars-Peter Clausen lars at metafoo.de
Sat Mar 23 14:36:37 CET 2013

On 03/23/2013 02:28 PM, Laxman Dewangan wrote:
> On Saturday 23 March 2013 06:59 PM, Lars-Peter Clausen wrote:
>> On 03/23/2013 02:16 PM, Laxman Dewangan wrote:
>>> On Saturday 23 March 2013 05:05 AM, Stephen Warren wrote:
>>>> On 03/22/2013 10:26 AM, Lars-Peter Clausen wrote:
>>>>> Hi,
>>>>> The tegra pcm driver tries to emulate SNDRV_PCM_TRIGGER_PAUSE and
>>>>> SNDRV_PCM_TRIGGER_STOP to snd_dmaengine_pcm_trigger. But does this really
>>>>> work? The old non-dmaengine based driver implemented this properly. I'd
>>>>> reset the dma position pointer for SNDRV_PCM_TRIGGER_START, but keep it
>>>>> where it was for SNDRV_PCM_TRIGGER_RESUME. But as far as I can see with
>>>>> the
>>>>> dmaengine based driver the pointer always gets reset to 0 for both
>>>> It's quite possible this hasn't been tested, or tested recently. I don't
>>>> recall how to test PAUSE/RESUME. Can you enlighten me?
>>>> Laxman, can you comment here?
>>> The tegra20/Tegra30 does not support the pause of the channel. It was
>>> through global pause. hence the pause and resume is implemented like stop
>>> transfer and again restart transfer. hence you are seeing this as the  reset
>>> pointer as 0.
>> Yea, but in that case you shouldn't implement pause/resume at all. You've
>> changed the semantics on pause/resume on which applications rely. If
>> pause/resume are not implemented applications usually workaround it.
>> - Lars
> So should we return -EINVAL in case of following?

Don't set the SNDRV_PCM_INFO_PAUSE and SNDRV_PCM_INFO_RESUME bits in the
pcm_hardware struct and use snd_dmaengine_pcm_trigger as your trigger
callback. The ALSA core will take care of everything else.

- Lars

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