On Fri, Jul 03, 2020 at 09:04:49AM -0700, Rob Clark wrote: > 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. Downstream does set it universally. There are some theoretical use cases where it might be beneficial to set it on a per-mapping basis with a bunch of hinting from userspace and nobody has tried to characterize this on real hardware so it is not clear to me if it is worth it. I think a domain wide attribute works for now but if a compelling per-mapping use case does comes down the pipeline we need to have a backup in mind - possibly a prot flag to disable NWA? Jordan > 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 -- The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
