linux-kernel - RE: [PATCH] dmaengine: fsl-edma: add PM suspend/resume support

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Date:	Fri, 17 Jul 2015 05:41:55 +0000
From:	Yao Yuan <yao.yuan@...escale.com>
To:	Vinod Koul <vinod.koul@...el.com>
CC:	"stefan@...er.ch" <stefan@...er.ch>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH] dmaengine: fsl-edma: add PM suspend/resume support

Hi Vinod,

eDMA sullpies the data transmission service for other IPs, so it should be suspended later and resumed earlier.
For example:
Synchronous Audio Interface (SAI), SAI use DMA to transfer the data.
When suspend:
1, SAI using suspend handlers to stop the DMA transmission.
2, DMA using suspend_late  handlers to check whether DMA chan is idle.
When resume:
1, DMA using resume_early   to enable. And then can servicing for others.
2, SAI using resume and then can use DMA to data transmission.

We must sure the order is right, so I think DMA should using early/late handlers.

Thanks.

Best Regards,
Yuan Yao

On Thursday, July 16, 2015 9:24 PM, Vinod wrote:
> On Wed, Jul 15, 2015 at 05:32:58PM +0800, Yuan Yao wrote:
> > +
> > +static const struct dev_pm_ops fsl_edma_pm_ops = {
> > +	.suspend_late   = fsl_edma_suspend_late,
> > +	.resume_early   = fsl_edma_resume_early,
> any reason why you are using early/late handlers?
> 
> --
> ~Vinod

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