Re: [PATCH 3/3] iommu/io-pgtable-arm: Allow coherent walks for Mali
From: Steven Price <steven.price@arm.com>
Date: 2019-09-12 10:54:10
Also in:
linux-iommu
On 11/09/2019 15:42, Robin Murphy wrote:
Midgard GPUs have ACE-Lite master interfaces which allows systems to integrate them in an I/O-coherent manner. It seems that from the GPU's viewpoint, the rest of the system is its outer shareable domain, and it will only emit snoop signals for outer shareable accesses. As such, setting the TTBR_SHARE_OUTER bit does indeed get coherent pagetable walks working nicely. Making data accesses coherent seems to be more of a challenge... Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com> Note the terminology in the GPU is *very* confusing here. Midgard refers to the system's inner shareable domain as "outer shareable", and uses "inner shareable" to mean purely within the GPU. For data access kbase sets up a different default MEMATTR if ACE is available: /* Set to implementation defined, outer caching */ #define AS_MEMATTR_LPAE_OUTER_IMPL_DEF 0x88ull [...] #define AS_MEMATTR_INDEX_DEFAULT_ACE 3 [...] /* Outer coherent, inner implementation defined policy */ #define AS_MEMATTR_INDEX_OUTER_IMPL_DEF 3 Steve
quoted hunk ↗ jump to hunk
--- drivers/iommu/io-pgtable-arm.c | 3 +++ 1 file changed, 3 insertions(+)diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c index 77f41c9dd9be..2794d4661339 100644 --- a/drivers/iommu/io-pgtable-arm.c +++ b/drivers/iommu/io-pgtable-arm.c@@ -1061,6 +1061,9 @@ arm_mali_lpae_alloc_pgtable(struct io_pgtable_cfg *cfg, void *cookie) cfg->arm_mali_lpae_cfg.transtab = virt_to_phys(data->pgd) | ARM_MALI_LPAE_TTBR_READ_INNER | ARM_MALI_LPAE_TTBR_ADRMODE_TABLE; + if (cfg->coherent_walk) + cfg->arm_mali_lpae_cfg.transtab |= ARM_MALI_LPAE_TTBR_SHARE_OUTER; + return &data->iop; out_free_data:
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