linux-kernel - Re: [PATCH] dma: tegra: implement suspend/resume callbacks

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Date:	Thu, 02 May 2013 12:42:30 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Vinod Koul <vinod.koul@...el.com>
CC:	Laxman Dewangan <ldewangan@...dia.com>, djbw@...com,
	linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma: tegra: implement suspend/resume callbacks

On 04/30/2013 04:30 AM, Vinod Koul wrote:
> On Wed, Apr 24, 2013 at 03:24:27PM +0530, Laxman Dewangan wrote:
>> Implement suspend/resume callbacks to store APB DMA channel's
>> register on suspend and restore APB DMA channel's register on
>> resume.
...
> You dont seem to handle suspend when DMA is active? Otherwise looks fine.
> Stephen, you okay with this patch?

Yes, I think this looks fine. Sorry for the slow response; I was on
vacation.

One question though: Laxman mentioned that DMA clients were responsible
for suspending their DMA accesses themselves. Does the dmaengine core
define the semantics here; are DMA drivers supposed to handle suspend
with active DMAs, or should DMA clients suspend their DMA accesses
themselves as Laxman suggests? If the latter, I wonder if we actually
need to save/restore all the registers, since after resume, a new DMA
access would be started in all cases, which would then reprogram the HW.
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