linux-kernel - Re: [PATCH v16 1/5] iommu/arm-smmu: Add pm

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Date:   Mon, 1 Oct 2018 16:02:17 +0530
From:   Vivek Gautam <vivek.gautam@...eaurora.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, alex.williamson@...hat.com,
        Linux PM <linux-pm@...r.kernel.org>, sboyd@...nel.org,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Will Deacon <will.deacon@....com>,
        open list <linux-kernel@...r.kernel.org>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        "robh+dt" <robh+dt@...nel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH v16 1/5] iommu/arm-smmu: Add pm_runtime/sleep ops

On Mon, Oct 1, 2018 at 11:19 AM Vivek Gautam
<vivek.gautam@...eaurora.org> wrote:
>
> HI Ulf,
>
> On Fri, Sep 28, 2018 at 5:30 PM Ulf Hansson <ulf.hansson@...aro.org> wrote:
> >
> > On 30 August 2018 at 16:45, Vivek Gautam <vivek.gautam@...eaurora.org> wrote:
> > > From: Sricharan R <sricharan@...eaurora.org>
> > >
> > > The smmu needs to be functional only when the respective
> > > master's using it are active. The device_link feature
> > > helps to track such functional dependencies, so that the
> > > iommu gets powered when the master device enables itself
> > > using pm_runtime. So by adapting the smmu driver for
> > > runtime pm, above said dependency can be addressed.
> > >
> > > This patch adds the pm runtime/sleep callbacks to the
> > > driver and also the functions to parse the smmu clocks
> > > from DT and enable them in resume/suspend.
> > >
> > > Also, while we enable the runtime pm add a pm sleep suspend
> > > callback that pushes devices to low power state by turning
> > > the clocks off in a system sleep.
> > > Also add corresponding clock enable path in resume callback.
> > >
> > > Signed-off-by: Sricharan R <sricharan@...eaurora.org>
> > > Signed-off-by: Archit Taneja <architt@...eaurora.org>
> > > [vivek: rework for clock and pm ops]
> > > Signed-off-by: Vivek Gautam <vivek.gautam@...eaurora.org>
> > > Reviewed-by: Tomasz Figa <tfiga@...omium.org>
> > > Tested-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
> > > ---
> > >  drivers/iommu/arm-smmu.c | 77 ++++++++++++++++++++++++++++++++++++++++++++++--
> > >  1 file changed, 74 insertions(+), 3 deletions(-)
> > > diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> >
> > [...]
> >
> > > -static int __maybe_unused arm_smmu_pm_resume(struct device *dev)
> > > +static int __maybe_unused arm_smmu_runtime_resume(struct device *dev)
> > >  {
> > >         struct arm_smmu_device *smmu = dev_get_drvdata(dev);
> > > +       int ret;
> > > +
> > > +       ret = clk_bulk_enable(smmu->num_clks, smmu->clks);
> > > +       if (ret)
> > > +               return ret;
> > >
> > >         arm_smmu_device_reset(smmu);
> > > +
> > >         return 0;
> > >  }
> > >
> > > -static SIMPLE_DEV_PM_OPS(arm_smmu_pm_ops, NULL, arm_smmu_pm_resume);
> > > +static int __maybe_unused arm_smmu_runtime_suspend(struct device *dev)
> > > +{
> > > +       struct arm_smmu_device *smmu = dev_get_drvdata(dev);
> > > +
> > > +       clk_bulk_disable(smmu->num_clks, smmu->clks);
> > > +
> > > +       return 0;
> > > +}
> > > +
> > > +static int __maybe_unused arm_smmu_pm_resume(struct device *dev)
> > > +{
> > > +       if (pm_runtime_suspended(dev))
> > > +               return 0;
> >
> > Looks like you should be able use pm_runtime_force_resume(), instead
> > of using this local trick. Unless I am missing something, of course.
> >
> > In other words, just assign the system sleep callbacks for resume, to
> > pm_runtime_force_resume(). And vice verse for the system suspend
> > callbacks, pm_runtime_force_suspend(), of course.
>
> Thanks for the review. I will change this as suggested.

Coming back at this - actually Rafael suggested _not_ to use
pm_runtime_force_suspend/resume() when Marek had suggested
the same [1].
He also mentioned few caveats/limitations of using these APIs
for system sleep ops.
Let me know your opinion. Thanks.

[1] https://lkml.org/lkml/2018/7/11/978
[2] https://lkml.org/lkml/2018/7/23/334

Best regards
Vivek
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