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

+Arnd

On 13 January 2017 at 08:26, Marek Szyprowski [off-list ref] 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