Re: [PATCHv3 7/7] drm/msm/a6xx: Add support for using system cache(LLC)

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:

quoted

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?

Thanks,
Sai

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