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Subject: Re: [PATCH v12 2/4] iommu/arm-smmu: Invoke pm_runtime during probe,
 add/remove device
To:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Tomasz Figa <tfiga@chromium.org>
Cc:     "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        "list@263.net:IOMMU DRIVERS" <iommu@lists.linux-foundation.org>,
        Joerg Roedel <joro@8bytes.org>, joro@8bytes.org,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        "list@263.net:IOMMU DRIVERS" <iommu@lists.linux-foundation.org>,
        Joerg Roedel <joro@8bytes.org>,
        iommu@lists.linux-foundation.org,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Alex Williamson <alex.williamson@redhat.com>,
        Rob Clark <robdclark@gmail.com>,
        Linux PM <linux-pm@vger.kernel.org>,
        freedreno <freedreno@lists.freedesktop.org>,
        Stephen Boyd <sboyd@kernel.org>,
        Sricharan R <sricharan@codeaurora.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Archit Taneja <architt@codeaurora.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        jcrouse@codeaurora.org
References: <20180708173413.1965-1-vivek.gautam@codeaurora.org>
 <20180708173413.1965-3-vivek.gautam@codeaurora.org>
 <1694664.FhRBrgajmF@aspire.rjw.lan>
 <CAAFQd5COVfXRBuq2ofHoOvNb+cMVmAFDaekh5KM4DBB1ZEf5pA@mail.gmail.com>
 <CAJZ5v0hMQJQ0Z-H2OLaeCdT+-MW_eSWmg7saVzkpDqJ-=i3DnQ@mail.gmail.com>
From:   Vivek Gautam <vivek.gautam@codeaurora.org>
Message-ID: <1bc641d5-a5d0-e459-57cf-07b6b7e055f4@codeaurora.org>
Date:   Wed, 11 Jul 2018 17:00:14 +0530
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On 7/11/2018 4:29 PM, Rafael J. Wysocki wrote:
> On Wed, Jul 11, 2018 at 12:05 PM, Tomasz Figa <tfiga@chromium.org> wrote:
>> Hi Rafael,
>>
>> Thanks for review.
>>
>> On Wed, Jul 11, 2018 at 6:53 PM Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
>>> On Sunday, July 8, 2018 7:34:11 PM CEST Vivek Gautam wrote:
>>>> From: Sricharan R <sricharan@codeaurora.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@codeaurora.org>
>>>> [vivek: Cleanup pm runtime calls]
>>>> Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
>>>> Reviewed-by: Tomasz Figa <tfiga@chromium.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.
> OK, so it is an optimization.  It would be good to put a comment in
> there to that effect.

Yea, actually there's a comment placed in arm_smmu_device_probe()
  where the runtime PM is conditionally enabled.
I can add comments for these wrappers too if you would like.

Thanks & Regards
Vivek