linux-kernel - Re: [PATCH v7 3/6] iommu/arm-smmu: Invoke pm_runtime during probe, add/remove device

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Message-ID: <CAFp+6iGOsAxg63+T_xzAh5VmiPPsJp_0WxQVb+U0T407OTxvMQ@mail.gmail.com>
Date:   Wed, 14 Feb 2018 13:58:47 +0530
From:   Vivek Gautam <vivek.gautam@...eaurora.org>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     "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>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will.deacon@....com>,
        Rob Clark <robdclark@...il.com>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        devicetree@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        David Airlie <airlied@...ux.ie>,
        Greg KH <gregkh@...uxfoundation.org>,
        Stephen Boyd <sboyd@...eaurora.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH v7 3/6] iommu/arm-smmu: Invoke pm_runtime during probe,
 add/remove device

Hi Tomasz,


On Tue, Feb 13, 2018 at 1:54 PM, Tomasz Figa <tfiga@...omium.org> wrote:
> Hi Vivek,
>
> Thanks for the patch. Please see my comments inline.
>
> On Wed, Feb 7, 2018 at 7:31 PM, Vivek Gautam
> <vivek.gautam@...eaurora.org> 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>
>> ---
>>  drivers/iommu/arm-smmu.c | 42 ++++++++++++++++++++++++++++++++++++++----
>>  1 file changed, 38 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
>> index 9e2f917e16c2..c024f69c1682 100644
>> --- a/drivers/iommu/arm-smmu.c
>> +++ b/drivers/iommu/arm-smmu.c
>> @@ -913,11 +913,15 @@ static void arm_smmu_destroy_domain_context(struct iommu_domain *domain)
>>         struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
>>         struct arm_smmu_device *smmu = smmu_domain->smmu;
>>         struct arm_smmu_cfg *cfg = &smmu_domain->cfg;
>> -       int irq;
>> +       int ret, irq;
>>
>>         if (!smmu || domain->type == IOMMU_DOMAIN_IDENTITY)
>>                 return;
>>
>> +       ret = pm_runtime_get_sync(smmu->dev);
>> +       if (ret)
>> +               return;
>
> pm_runtime_get_sync() will return 0 if the device was powered off, 1
> if it was already/still powered on or runtime PM is not compiled in,
> or a negative value on error, so shouldn't the test be (ret < 0)?

Yes, I too noticed it while i was testing on a different platform, and
was hitting
a failure case. Will update at all places.

>
> Moreover, I'm actually wondering if it makes any sense to power up the
> hardware just to program it and power it down again. In a system where
> the IOMMU is located within a power domain, it would cause the IOMMU
> block to lose its state anyway.
>
> Actually, reflecting back on "[PATCH v7 2/6] iommu/arm-smmu: Add
> pm_runtime/sleep ops", perhaps it would make more sense to just
> control the clocks independently of runtime PM? Then, runtime PM could
> be used for real power management, e.g. really powering the block up
> and down, for further power saving.
>
> +Generally similar comments for other places in this patch.
>
>> +
>>         /*
>>          * Disable the context bank and free the page tables before freeing
>>          * it.
>> @@ -932,6 +936,8 @@ static void arm_smmu_destroy_domain_context(struct iommu_domain *domain)
>>
>>         free_io_pgtable_ops(smmu_domain->pgtbl_ops);
>>         __arm_smmu_free_bitmap(smmu->context_map, cfg->cbndx);
>> +
>> +       pm_runtime_put_sync(smmu->dev);
>
> Is there any point in the put being sync here?

No, I don't think. Can manage with just a 'put' here. Will modify.

best regards
Vivek

>
> [snip]
>
>> @@ -2131,6 +2152,14 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
>>         if (err)
>>                 return err;
>>
>> +       platform_set_drvdata(pdev, smmu);
>> +
>> +       pm_runtime_enable(dev);
>
> I suspect this may be a disaster for systems where IOMMUs are located
> inside power domains, because the driver doesn't take care of the
> IOMMU block losing its state on physical power down, as I mentioned in
> my comments above.
>
> Best regards,
> Tomasz



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