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

From: Sai Prakash Ranjan
Date: Fri Jul 03 2020 - 10:53:13 EST


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?

Thanks,
Sai

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