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

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Message-ID: <CAHbNUh0fVND_oGLXWzsyKzbmJc_=FqhZTAnVHE4GGZ5aaJQbEg@mail.gmail.com>
Date:	Wed, 14 May 2014 17:37:03 +0530
From:	Tushar Behera <tushar.behera@...aro.org>
To:	Jassi Brar <jassisinghbrar@...il.com>
Cc:	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 17:29, 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.

> DMA_PAUSE means freezing the transfer, not dropping it. DMA_RESUME
> then moves the transfer again from that point. Clubbing PAUSE with
> TERMINATE is plain wrong.  Sorry.
>

Would you please suggest how should we go ahead with implementing
DMA_PAUSE/DMA_RESUME support for PL330 driver?

> Regards
> Jassi

Thanks,
-- 
Tushar Behera
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