linux-kernel - Re: [PATCH v12 2/4] iommu/arm-smmu: Invoke pm

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Date:   Wed, 11 Jul 2018 19:05:06 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Vivek Gautam <vivek.gautam@...eaurora.org>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <joro@...tes.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will.deacon@....com>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        devicetree@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Rob Clark <robdclark@...il.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>, sboyd@...nel.org,
        Sricharan R <sricharan@...eaurora.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Archit Taneja <architt@...eaurora.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        jcrouse@...eaurora.org
Subject: Re: [PATCH v12 2/4] iommu/arm-smmu: Invoke pm_runtime during probe,
 add/remove device

Hi Rafael,

Thanks for review.

On Wed, Jul 11, 2018 at 6:53 PM Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>
> On Sunday, July 8, 2018 7:34:11 PM CEST Vivek Gautam wrote:
> > From: Sricharan R <sricharan@...eaurora.org>
> >
> > The smmu device probe/remove and add/remove master device callbacks
> > gets called when the smmu is not linked to its master, that is without
> > the context of the master device. So calling runtime apis in those places
> > separately.
> >
> > Signed-off-by: Sricharan R <sricharan@...eaurora.org>
> > [vivek: Cleanup pm runtime calls]
> > Signed-off-by: Vivek Gautam <vivek.gautam@...eaurora.org>
> > Reviewed-by: Tomasz Figa <tfiga@...omium.org>
> > ---
> >
> >  - Change since v11
> >    * Replaced pm_runtime_disable() with pm_runtime_force_suspend()
> >      to avoid warning about " Unpreparing enabled clock".
> >      Full warning text mentioned in cover patch.
> >
> >  drivers/iommu/arm-smmu.c | 92 +++++++++++++++++++++++++++++++++++++++++++-----
> >  1 file changed, 84 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> > index a01d0dde21dd..09265e206e2d 100644
> > --- a/drivers/iommu/arm-smmu.c
> > +++ b/drivers/iommu/arm-smmu.c
> > @@ -268,6 +268,20 @@ static struct arm_smmu_option_prop arm_smmu_options[] = {
> >       { 0, NULL},
> >  };
> >
> > +static inline int arm_smmu_rpm_get(struct arm_smmu_device *smmu)
> > +{
> > +     if (pm_runtime_enabled(smmu->dev))
>
> Why do you need the pm_runtime_enabled() checks here and below?
>
> pm_runtime_get_sync() and pm_runtime_put() should work just fine if
> runtime PM is not enabled.

Because pm_runtime_get_sync() acquires a spin lock, even if only for
the short time of checking if runtime PM is enabled and SMMU driver
maintainers didn't want any spin locks in certain IOMMU API code paths
on hardware implementations that don't need runtime PM, while we still
need to be able to control runtime PM there on hardware
implementations that need so.

Best regards,
Tomasz