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

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Date:   Wed, 12 Jul 2017 23:48:43 -0700
From:   Stephen Boyd <sboyd@...eaurora.org>
To:     Vivek Gautam <vivek.gautam@...eaurora.org>
Cc:     joro@...tes.org, robin.murphy@....com, robh+dt@...nel.org,
        mark.rutland@....com, will.deacon@....com,
        m.szyprowski@...sung.com, robdclark@...il.com,
        iommu@...ts.linux-foundation.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, sricharan@...eaurora.org,
        stanimir.varbanov@...aro.org, architt@...eaurora.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 07/13, 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?
> 

While removing the spinlock around the map/unmap path may be one
thing, I'm not sure that's all of them. Is there a path from an
atomic DMA allocation (GFP_ATOMIC sort of thing) mapped into an
IOMMU for a device that can eventually get down to here and
attempt to turn a clk on?

-- 
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