Re: [PATCH] iommu/arm-smmu: Add clk_bulk_{prepare/unprepare} to system pm callbacks

[Sai Prakash Ranjan]

Hi Robin,

On 2021-07-27 16:03, Robin Murphy wrote:
> On 2021-07-27 11:25, Robin Murphy wrote:
> > On 2021-07-27 10:33, Sai Prakash Ranjan wrote:
> > > Some clocks for SMMU can have parent as XO such as 
> > > gpu_cc_hub_cx_int_clk
> > > of GPU SMMU in QTI SC7280 SoC and in order to enter deep sleep states 
> > > in
> > > such cases, we would need to drop the XO clock vote in unprepare call 
> > > and
> > > this unprepare callback for XO is in RPMh (Resource Power 
> > > Manager-Hardened)
> > > clock driver which controls RPMh managed clock resources for new QTI 
> > > SoCs
> > > and is a blocking call.
> > >
> > > Given we cannot have a sleeping calls such as clk_bulk_prepare() and
> > > clk_bulk_unprepare() in arm-smmu runtime pm callbacks since the iommu
> > > operations like map and unmap can be in atomic context and are in 
> > > fast
> > > path, add this prepare and unprepare call to drop the XO vote only 
> > > for
> > > system pm callbacks since it is not a fast path and we expect the 
> > > system
> > > to enter deep sleep states with system pm as opposed to runtime pm.
> > >
> > > This is a similar sequence of clock requests (prepare,enable and
> > > disable,unprepare) in arm-smmu probe and remove.
> >
> > Nope. We call arm_smmu_rpm_get(), which may resume the device, from 
> > atomic contexts. clk_prepare() may sleep. This doesn't work.
>
> Urgh, or maybe I skimmed the commit message too lightly *and* managed
> to totally misread the patch, sorry :(
>
> I'll wake up some more and try again later...

No worries, we took our time looking through that many times before 
posting this :)

Thanks,
Sai

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