Re: [PATCH v2] dmaengine: fsl-edma: add PM suspend/resume support

From: Li Yang
Date: Fri Aug 14 2015 - 19:48:43 EST

On Fri, Aug 14, 2015 at 1:24 AM, Yao Yuan <yao.yuan@xxxxxxxxxxxxx> wrote:
> Hi Leo,
> Thanks for your review.
> About those two methods for DMA suspend that you have mentioned. We have a lot of the discussions in other DMA driver like DMA for Freescale PowerPC.
> Finally, we think the device which used the DMA transmission service should cancel the transmission service in its suspend.
> So DMA in suspend should be idle.

If that's the case you should clearly state this in the commit message
and in code, although I don't know if it is safe to make such
assumption. There could be user of the DMA that doesn't track the
completion of transfers.

> Once the DMA in late_suspend is not be idle, we think some driver haven't canceled the DMA transmission. So maybe something is error when other driver in suspend.
> In the case, we should return failed to stop PM. DMA should not make a choice for other drivers(which used DMA) to force stop DMA transmission.

The suspend entrance should be terminated by wakeup events and only
critical issues. I don't think we should just terminate the suspend
entrance just because having on-going I/O without even try to stop it.

> Thanks.
> Best Regards,
> Yuan Yao
>> -----Original Message-----
>> From: pku.leo@xxxxxxxxx [mailto:pku.leo@xxxxxxxxx] On Behalf Of Li Yang
>> Sent: Friday, August 14, 2015 4:58 AM
>> To: Yuan Yao-B46683
>> Cc: Vinod Koul; stefan@xxxxxxxx; Arnd Bergmann; Dan Williams;
>> dmaengine@xxxxxxxxxxxxxxx; lkml; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-
>> pm@xxxxxxxxxxxxxxx
>> Subject: Re: [PATCH v2] dmaengine: fsl-edma: add PM suspend/resume
>> support
>> On Tue, Jul 21, 2015 at 3:56 AM, Yuan Yao <yao.yuan@xxxxxxxxxxxxx> wrote:
>> > This add power management suspend/resume support for the fsl-edma
>> > driver.
>> >
>> > eDMA acted as a basic function used by others. What it needs to do is
>> > the two steps below to support power management.
>> >
>> > In fsl_edma_suspend_late:
>> > Check whether the DMA chan is idle and if it is not idle, stop PM
>> > operation.
>> You should try to quiesce the device on suspend instead of depending on itself
>> to be happen in idle and failing if it is not.
>> Regards,
>> Leo

- Leo
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