[PATCH v4 0/4] DMA Engine: switch PL330 driver to non-irq-safe runtime PM

[Ulf Hansson]

+Arnd

On 13 January 2017 at 08:26, Marek Szyprowski <m.szyprowski at samsung.com> wrote:
> Hello,
>
> This patchset changes the way the runtime PM is implemented in the PL330 DMA
> engine driver. The main goal of such change is to add support for the audio
> power domain to Exynos5 SoCs (5250, 542x, 5433, probably others) and let
> it to be properly turned off, when no audio is being used. Switching to
> non-irq-safe runtime PM is required to properly let power domain to be
> turned off (irq-safe runtime PM keeps power domain turned on all the time)
> and to integrate with clock controller's runtime PM (this cannot be
> workarounded any other way, PL330 uses clocks from the controller, which
> belongs to the same power domain).
>
> For more details of the proposed change to the PL330 driver see patch #4.
>
> Audio power domain on Exynos5 SoCs contains following hardware modules:
> 1. clock controller
> 2. pin controller
> 3. PL330 DMA controller
> 4. I2S audio controller
>
> Patches for adding or fixing runtime PM for each of the above devices is
> handled separately.
>
> Runtime PM patches for clock controllers is possible and has been proposed
> in the following thread (pending review): "[PATCH v4 0/4] Add runtime PM
> support for clocks (on Exynos SoC example)",
> http://www.spinics.net/lists/arm-kernel/msg550747.html
>
> Runtime PM support for Exynos pin controller has been posted in the
> following thread: "[PATCH 0/9] Runtime PM for Exynos pin controller driver",
> http://www.spinics.net/lists/arm-kernel/msg550161.html
>
> Exynos I2S driver supports runtime PM, but some fixes were needed for it
> and they are already queued to linux-next.
>
> This patchset is based on linux-next from 13th January 2017 with "dmaengine:
> pl330: fix double lock" patch applied.
>
> Best regards
> Marek Szyprowski
> Samsung R&D Institute Poland


Marek, this is great work! It's been on my TODO list forever, so I
really appreciate your work here.

I did only a brief review so far, particularly concentrating on the
changes for device links and runtime PM. I like it!

Perhaps we can get someone like Arnd/Vinod to comment in general idea
from a DT and DMA slave channel point of view. I don't know that stuff
good enough to give good opinion.

A couple of things that crosses my mind so far:
1) I have planned to extend pm_runtime_force_suspend|resume() to cover
also device links. Seems like that becomes really useful together with
these changes.
2) I think there will be some corner cases during system
suspend/resume for pl330. Not sure yet though. However, fixing 1) and
converting the driver to use pm_runtime_force_suspend|resume() should
probably work anyway.

Allow me to help out looking into 1) and 2). If not for pl330, I am
pretty sure it will be useful for other DMA controllers that
implements device links and runtime PM.

[...]

Kind regards
Uffe