On Fri, Jul 3, 2020 at 7:53 AM Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx> wrote: > > Hi Will, > > On 2020-07-03 19:07, Will Deacon wrote: > > On Mon, Jun 29, 2020 at 09:22:50PM +0530, Sai Prakash Ranjan wrote: > >> diff --git a/drivers/gpu/drm/msm/msm_iommu.c > >> b/drivers/gpu/drm/msm/msm_iommu.c > >> index f455c597f76d..bd1d58229cc2 100644 > >> --- a/drivers/gpu/drm/msm/msm_iommu.c > >> +++ b/drivers/gpu/drm/msm/msm_iommu.c > >> @@ -218,6 +218,9 @@ static int msm_iommu_map(struct msm_mmu *mmu, > >> uint64_t iova, > >> iova |= GENMASK_ULL(63, 49); > >> > >> > >> + if (mmu->features & MMU_FEATURE_USE_SYSTEM_CACHE) > >> + prot |= IOMMU_SYS_CACHE_ONLY; > > > > Given that I think this is the only user of IOMMU_SYS_CACHE_ONLY, then > > it > > looks like it should actually be a property on the domain because we > > never > > need to configure it on a per-mapping basis within a domain, and > > therefore > > it shouldn't be exposed by the IOMMU API as a prot flag. > > > > Do you agree? > > > > GPU being the only user is for now, but there are other clients which > can use this. > Plus how do we set the memory attributes if we do not expose this as > prot flag? It does appear that the downstream kgsl driver sets this for basically all mappings.. well there is some conditional stuff around DOMAIN_ATTR_USE_LLC_NWA but it seems based on the property of the domain. (Jordan may know more about what that is about.) But looks like there are a lot of different paths into iommu_map in kgsl so I might have missed something. Assuming there isn't some case where we specifically don't want to use the system cache for some mapping, I think it could be a domain attribute that sets an io_pgtable_cfg::quirks flag BR, -R
