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

[Rob Clark]

On Mon, Aug 2, 2021 at 9:12 AM Will Deacon <will@xxxxxxxxxx> wrote:
>
> On Tue, Jul 27, 2021 at 03:03:22PM +0530, 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.
> >
> > Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
> > Co-developed-by: Rajendra Nayak <rnayak@xxxxxxxxxxxxxx>
> > Signed-off-by: Rajendra Nayak <rnayak@xxxxxxxxxxxxxx>
> > ---
> >  drivers/iommu/arm/arm-smmu/arm-smmu.c | 20 ++++++++++++++++++--
> >  1 file changed, 18 insertions(+), 2 deletions(-)
>
> [+Rob]
>
> How does this work with that funny GPU which writes to the SMMU registers
> directly? Does the SMMU need to remain independently clocked for that to
> work or is it all in the same clock domain?

AFAIU the device_link stuff should keep the SMMU clocked as long as
the GPU is alive, so I think this should work out ok.. ie. the SMMU
won't suspend while the GPU is not suspended.

BR,
-R


> > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > index d3c6f54110a5..9561ba4c5d39 100644
> > --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > @@ -2277,6 +2277,13 @@ static int __maybe_unused arm_smmu_runtime_suspend(struct device *dev)
> >
> >  static int __maybe_unused arm_smmu_pm_resume(struct device *dev)
> >  {
> > +     int ret;
> > +     struct arm_smmu_device *smmu = dev_get_drvdata(dev);
> > +
> > +     ret = clk_bulk_prepare(smmu->num_clks, smmu->clks);
> > +     if (ret)
> > +             return ret;
> > +
> >       if (pm_runtime_suspended(dev))
> >               return 0;
>
> If we subsequently fail to enable the clks in arm_smmu_runtime_resume()
> should we unprepare them again?
>
> Will
>
> > @@ -2285,10 +2292,19 @@ static int __maybe_unused arm_smmu_pm_resume(struct device *dev)
> >
> >  static int __maybe_unused arm_smmu_pm_suspend(struct device *dev)
> >  {
> > +     int ret = 0;
> > +     struct arm_smmu_device *smmu = dev_get_drvdata(dev);
> > +
> >       if (pm_runtime_suspended(dev))
> > -             return 0;
> > +             goto clk_unprepare;
> >
> > -     return arm_smmu_runtime_suspend(dev);
> > +     ret = arm_smmu_runtime_suspend(dev);
> > +     if (ret)
> > +             return ret;
> > +
> > +clk_unprepare:
> > +     clk_bulk_unprepare(smmu->num_clks, smmu->clks);
> > +     return ret;
> >  }
> >
> >  static const struct dev_pm_ops arm_smmu_pm_ops = {
> > --
> > QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
> > of Code Aurora Forum, hosted by The Linux Foundation
> >
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