Re: [PATCH v14 0/4] iommu/arm-smmu: Add runtime pm/sleep support

On 20/08/18 10:31, Tomasz Figa wrote:

Hi Robin,

On Fri, Jul 27, 2018 at 4:02 PM Vivek Gautam
[off-list ref] wrote:

quoted

This series provides the support for turning on the arm-smmu's
clocks/power domains using runtime pm. This is done using
device links between smmu and client devices. The device link
framework keeps the two devices in correct order for power-cycling
across runtime PM or across system-wide PM.

With addition of a new device link flag DL_FLAG_AUTOREMOVE_SUPPLIER [8]
(available in linux-next of Rafael's linux-pm tree [9]), the device links
created between arm-smmu and its clients will be automatically purged
when arm-smmu driver unbinds from its device.

As not all implementations support clock/power gating, we are checking
for a valid 'smmu->dev's pm_domain' to conditionally enable the runtime
power management for such smmu implementations that can support it.
Otherwise, the clocks are turned to be always on in .probe until .remove.
With conditional runtime pm now, we avoid touching dev->power.lock
in fastpaths for smmu implementations that don't need to do anything
useful with pm_runtime.
This lets us to use the much-argued pm_runtime_get_sync/put_sync()
calls in map/unmap callbacks so that the clients do not have to
worry about handling any of the arm-smmu's power.

This series also adds support for Qcom's arm-smmu-v2 variant that
has different clocks and power requirements.

Previous version of this patch series is @ [2].

Tested this series on msm8996, and sdm845 after pulling in Rafael's linux-pm
linux-next[9] and Joerg's iommu next[10] branches, and related changes for
device tree, etc.

Hi Robin, Will,
I have addressed the comments for v13. If there's still a chance
can you please consider pulling this for v4.19.
Thanks.

[v14]
    * Moved arm_smmu_device_reset() from arm_smmu_pm_resume() to
      arm_smmu_runtime_resume() so that the pm_resume callback calls
      only runtime_resume to resume the device.
      This should take care of restoring the state of smmu in systems
      in which smmu lose register state on power-domain collapse.

It's been a while since this series was posted and no more comments
seem to be left anymore. Would you have some time to take a look
again? Thanks.

Other than the binding issue which turned up in the meantime, I *think* 
this is looking OK now in terms of being sufficiently safe for all the 
various awkward retention vs. state-loss combinations. There's almost 
certainly still ways to improve it in future, but what we have now seems 
like a reasonable starting point that isn't impossibly complicated to 
reason about.

Robin.