Messages in this thread | | | Subject | Re: [PATCH V4 3/6] iommu/arm-smmu: Invoke pm_runtime during probe, add/remove device | From | Marek Szyprowski <> | Date | Thu, 13 Jul 2017 14:23:54 +0200 |
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Hi Rob,
On 2017-07-13 14:10, Rob Clark wrote: > On Thu, Jul 13, 2017 at 8:02 AM, Marek Szyprowski > <m.szyprowski@samsung.com> wrote: >> 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. >> > that seems like an interesting approach.. although I wonder if there > can be some race w/ new device memory access once clks are enabled > before tlb flush completes? That would be rather bad, since this > approach is letting the backing pages of memory be freed before tlb > flush.
Exynos IOMMU has spinlock for ensuring that there is no race between PM runtime suspend and unmap/tlb flush.
Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
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