Date:   Mon, 1 Oct 2018 15:51:56 +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 3:09 PM Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> On 1 October 2018 at 07:49, 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.
> >
> >>
> >> > +
> >> > +       return arm_smmu_runtime_resume(dev);
> >> > +}
> >> > +
> >> > +static int __maybe_unused arm_smmu_pm_suspend(struct device *dev)
> >> > +{
> >> > +       if (pm_runtime_suspended(dev))
> >> > +               return 0;
> >> > +
> >> > +       return arm_smmu_runtime_suspend(dev);
> >> > +}
> >> > +
> >> > +static const struct dev_pm_ops arm_smmu_pm_ops = {
> >> > +       SET_SYSTEM_SLEEP_PM_OPS(arm_smmu_pm_suspend, arm_smmu_pm_resume)
> >>
> >> I am wondering if using the ->suspend|resume() callback is really
> >> "late/early" enough in the device suspend phase?
> >>
> >> Others is using the noirq phase and some is even using the syscore
> >> ops. Of course it depends on the behavior of the consumers of iommu
> >> device, and I guess not everyone is using device links, which for sure
> >> improves things in this regards as well.
> >
> > Well yes, as you said the device links should be able to take care of
> > maintaining the correct suspend/resume order of smmu and its clients,
> > or am I missing your point here?
> > Let me know and I will be happy to incorporate any suggestions.
> > Thanks
>
> If it works fine, then you may keep it as is.
>
> Just wanted to point out that if any consumers relies on the iommu to
> operational to say until the suspend-late phase, then this doesn't
> play. Then you need to move your callbacks to the corresponding same
> phase.

Although I have no means to test the suspend-late phase, tests with graphics
and display on db820 haven't shown any anomaly.

[snip]

Best regards
Vivek

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