linux-kernel - Re: [PATCH V4 3/6] iommu/arm-smmu: Invoke pm_runtime during probe, add/remove device

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Message-ID: <CAF6AEGsFOtsOjt1sLNPSFLEcu-7d1zxCOhTeC+P8e0TDbb1dSA@mail.gmail.com>
Date:   Thu, 13 Jul 2017 07:50:31 -0400
From:   Rob Clark <robdclark@...il.com>
To:     Sricharan R <sricharan@...eaurora.org>
Cc:     Vivek Gautam <vivek.gautam@...eaurora.org>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Joerg Roedel <joro@...tes.org>,
        Robin Murphy <robin.murphy@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will.deacon@....com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        Archit Taneja <architt@...eaurora.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH V4 3/6] iommu/arm-smmu: Invoke pm_runtime during probe,
 add/remove device

On Thu, Jul 13, 2017 at 1:35 AM, Sricharan R <sricharan@...eaurora.org> wrote:
> Hi Vivek,
>
> On 7/13/2017 10:43 AM, Vivek Gautam wrote:
>> Hi Stephen,
>>
>>
>> On 07/13/2017 04:24 AM, Stephen Boyd wrote:
>>> On 07/06, Vivek Gautam wrote:
>>>> @@ -1231,12 +1237,18 @@ static int arm_smmu_map(struct iommu_domain *domain, unsigned long iova,
>>>>   static size_t arm_smmu_unmap(struct iommu_domain *domain, unsigned long iova,
>>>>                    size_t size)
>>>>   {
>>>> -    struct io_pgtable_ops *ops = to_smmu_domain(domain)->pgtbl_ops;
>>>> +    struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
>>>> +    struct io_pgtable_ops *ops = smmu_domain->pgtbl_ops;
>>>> +    size_t ret;
>>>>         if (!ops)
>>>>           return 0;
>>>>   -    return ops->unmap(ops, iova, size);
>>>> +    pm_runtime_get_sync(smmu_domain->smmu->dev);
>>> Can these map/unmap ops be called from an atomic context? I seem
>>> to recall that being a problem before.
>>
>> That's something which was dropped in the following patch merged in master:
>> 523d7423e21b iommu/arm-smmu: Remove io-pgtable spinlock
>>
>> Looks like we don't  need locks here anymore?
>
>  Apart from the locking, wonder why a explicit pm_runtime is needed
>  from unmap. Somehow looks like some path in the master using that
>  should have enabled the pm ?
>

Yes, there are a bunch of scenarios where unmap can happen with
disabled master (but not in atomic context).  On the gpu side we
opportunistically keep a buffer mapping until the buffer is freed
(which can happen after gpu is disabled).  Likewise, v4l2 won't unmap
an exported dmabuf while some other driver holds a reference to it
(which can be dropped when the v4l2 device is suspended).

Since unmap triggers tbl flush which touches iommu regs, the iommu
driver *definitely* needs a pm_runtime_get_sync().

BR,
-R