On Fri, Jul 14, 2017 at 1:07 PM, Will Deacon <will.deacon@xxxxxxx> wrote: > On Thu, Jul 13, 2017 at 10:55:10AM -0400, Rob Clark wrote: >> On Thu, Jul 13, 2017 at 9:53 AM, Sricharan R <sricharan@xxxxxxxxxxxxxx> wrote: >> > Hi, >> > >> > On 7/13/2017 5:20 PM, Rob Clark wrote: >> >> On Thu, Jul 13, 2017 at 1:35 AM, Sricharan R <sricharan@xxxxxxxxxxxxxx> 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(). >> > >> > Ok, with that being the case, there are two things here, >> > >> > 1) If the device links are still intact at these places where unmap is called, >> > then pm_runtime from the master would setup the all the clocks. That would >> > avoid reintroducing the locking indirectly here. >> > >> > 2) If not, then doing it here is the only way. But for both cases, since >> > the unmap can be called from atomic context, resume handler here should >> > avoid doing clk_prepare_enable , instead move the clk_prepare to the init. >> > >> >> I do kinda like the approach Marek suggested.. of deferring the tlb >> flush until resume. I'm wondering if we could combine that with >> putting the mmu in a stalled state when we suspend (and not resume the >> mmu until after the pending tlb flush)? > > I'm not sure that a stalled state is what we're after here, because we need > to take care to prevent any table walks if we've freed the underlying pages. > What we could try to do is disable the SMMU (put into global bypass) and > invalidate the TLB when performing a suspend operation, then we just ignore > invalidation whilst the clocks are stopped and, on resume, enable the SMMU > again. wouldn't stalled just block any memory transactions by device(s) using the context bank? Putting it in bypass isn't really a good thing if there is any chance the device can sneak in a memory access before we've taking it back out of bypass (ie. makes gpu a giant userspace controlled root hole). BR, -R > That said, I don't think we can tolerate suspend/resume racing with > map/unmap, and it's not clear to me how we avoid that without penalising > the fastpath. > > Will -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html