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

[Robin Murphy]

On 20/08/18 10:31, Tomasz Figa wrote:
> Hi Robin,
>
> On Fri, Jul 27, 2018 at 4:02 PM Vivek Gautam
> <vivek.gautam@xxxxxxxxxxxxxx> wrote:
> > 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.