linux-kernel - Re: [PATCH] dma: pl330: Add support for DMA

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Message-ID: <537513A8.701@metafoo.de>
Date:	Thu, 15 May 2014 21:21:12 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Tushar Behera <tushar.behera@...aro.org>
CC:	Jassi Brar <jassisinghbrar@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	dmaengine@...r.kernel.org, Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Linux-ALSA <alsa-devel@...a-project.org>,
	Takashi Iwai <tiwai@...e.de>
Subject: Re: [PATCH] dma: pl330: Add support for DMA_PAUSE command

On 05/15/2014 02:01 PM, Tushar Behera wrote:
> On 14 May 2014 17:54, Lars-Peter Clausen <lars@...afoo.de> wrote:
>> On 05/14/2014 02:07 PM, Tushar Behera wrote:
>>>
>>> On 14 May 2014 17:29, Jassi Brar <jassisinghbrar@...il.com> wrote:
>>>>
>>>> On Wed, May 14, 2014 at 8:53 AM, Tushar Behera <tushar.behera@...aro.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.

Are you seeing an actual issue that you are trying to fix with your patch?

- Lars

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