On Thu, Jul 13, 2017 at 5:50 AM, Robin Murphy <robin.mur...@arm.com> wrote: > On 13/07/17 07:48, Stephen Boyd wrote: >> 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? > > Yes, in the DMA path map/unmap will frequently be called from IRQ > handlers (think e.g. network packets). The whole point of removing the > lock was to allow multiple maps/unmaps to execute in parallel (since we > know they will be safely operating on different areas of the pagetable). > AFAICS this change is going to largely reintroduce that bottleneck via > dev->power_lock, which is anything but what we want :( >
Maybe __pm_runtime_resume() needs some sort of fast-path if already enabled? Or otherwise we need some sort of flag to tell the iommu that it cannot rely on the unmapping device to be resumed? BR, -R