Subject: Re: [PATCH V4 3/6] iommu/arm-smmu: Invoke pm_runtime during probe,
 add/remove device
To: Rob Clark <robdclark@gmail.com>,
        Sricharan R <sricharan@codeaurora.org>
Cc: Vivek Gautam <vivek.gautam@codeaurora.org>,
        Stephen Boyd <sboyd@codeaurora.org>, Joerg Roedel <joro@8bytes.org>,
        Robin Murphy <robin.murphy@arm.com>, Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>, Will Deacon <will.deacon@arm.com>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-clk <linux-clk@vger.kernel.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Stanimir Varbanov <stanimir.varbanov@linaro.org>,
        Archit Taneja <architt@codeaurora.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>
From: Marek Szyprowski <m.szyprowski@samsung.com>
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Date: Thu, 13 Jul 2017 14:02:40 +0200
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Hi All,

On 2017-07-13 13:50, Rob Clark wrote:
> On Thu, Jul 13, 2017 at 1:35 AM, Sricharan R <sricharan@codeaurora.org> wrote:
>> On 7/13/2017 10:43 AM, Vivek Gautam wrote:
>>> 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().

Afair unmap might be called from atomic context as well, for example as
a result of dma_unmap_page(). In exynos IOMMU I simply check the runtime
PM state of IOMMU device. TLB flush is performed only when IOMMU is in 
active
state. If it is suspended, I assume that the IOMMU controller's context
is already lost and its respective power domain might be already turned off,
so there is no point in touching IOMMU registers.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland