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

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Date:	Thu, 15 May 2014 17:31:15 +0530
From:	Tushar Behera <tushar.behera@...aro.org>
To:	Lars-Peter Clausen <lars@...afoo.de>
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>
Subject: Re: [PATCH] dma: pl330: Add support for DMA_PAUSE command

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?


-- 
Tushar Behera
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