[3/3] iommu/io-pgtable-arm: Allow coherent walks for Mali
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Message ID 8eb563978e7e872ddde45c0413e1a3f30b792658.1568211045.git.robin.murphy@arm.com
State New
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  • iommu/io-pgtable-arm: Mali LPAE improvements
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Commit Message

Robin Murphy Sept. 11, 2019, 2:42 p.m. UTC
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>
---
 drivers/iommu/io-pgtable-arm.c | 3 +++
 1 file changed, 3 insertions(+)

Comments

Steven Price Sept. 12, 2019, 10:53 a.m. UTC | #1
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

> ---
>  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:
>

Patch
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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: