On Fri, Jun 15, 2018 at 05:52:32PM +0100, Will Deacon wrote: > Hi Vivek, > > On Fri, Jun 15, 2018 at 04:23:29PM +0530, Vivek Gautam wrote: > > Qualcomm SoCs have an additional level of cache called as > > System cache or Last level cache[1]. This cache sits right > > before the DDR, and is tightly coupled with the memory > > controller. > > The cache is available to all the clients present in the > > SoC system. The clients request their slices from this system > > cache, make it active, and can then start using it. For these > > clients with smmu, to start using the system cache for > > dma buffers and related page tables [2], few of the memory > > attributes need to be set accordingly. > > This change makes the related memory Outer-Shareable, and > > updates the MAIR with necessary protection. > > > > The MAIR attribute requirements are: > > Inner Cacheablity = 0 > > Outer Cacheablity = 1, Write-Back Write Allocate > > Outer Shareablity = 1 > > Hmm, so is this cache coherent with the CPU or not? Why don't normal > non-cacheable mappings allocated in the LLC by default? > > > diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c > > index f7a96bcf94a6..8058e7205034 100644 > > --- a/drivers/iommu/arm-smmu.c > > +++ b/drivers/iommu/arm-smmu.c > > @@ -249,6 +249,7 @@ struct arm_smmu_domain { > > struct mutex init_mutex; /* Protects smmu pointer */ > > spinlock_t cb_lock; /* Serialises ATS1* ops and TLB syncs */ > > struct iommu_domain domain; > > + bool has_sys_cache; > > }; > > > > struct arm_smmu_option_prop { > > @@ -862,6 +863,8 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain, > > > > if (smmu->features & ARM_SMMU_FEAT_COHERENT_WALK) > > pgtbl_cfg.quirks = IO_PGTABLE_QUIRK_NO_DMA; > > + if (smmu_domain->has_sys_cache) > > + pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_SYS_CACHE; > > > > smmu_domain->smmu = smmu; > > pgtbl_ops = alloc_io_pgtable_ops(fmt, &pgtbl_cfg, smmu_domain); > > @@ -1477,6 +1480,9 @@ static int arm_smmu_domain_get_attr(struct iommu_domain *domain, > > case DOMAIN_ATTR_NESTING: > > *(int *)data = (smmu_domain->stage == ARM_SMMU_DOMAIN_NESTED); > > return 0; > > + case DOMAIN_ATTR_USE_SYS_CACHE: > > + *((int *)data) = smmu_domain->has_sys_cache; > > + return 0; > > I really don't like exposing this to clients directly like this, > particularly as there aren't any in-tree users. I would prefer that we > provide a way for the io-pgtable code to have its MAIR values overridden > so that all non-coherent DMA ends up using the system cache. FWIW here is a future in-tree user for LLC: https://patchwork.freedesktop.org/series/40545/ Specifically: https://patchwork.freedesktop.org/patch/212400/ Jordan -- The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html