Subject: Re: [PATCH v2 1/3] iommu/io-pgtable-arm: Support coherency for Mali LPAE

From: Boris Brezillon <[email-masked]>
Date: Mon, 5 Oct 2020 16:50:08 +0200

On Tue, 22 Sep 2020 15:16:48 +0100
Robin Murphy <[email-masked]> 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 so
> even when snoop signals are wired up, they are only emitted for outer
> shareable accesses. As such, setting the TTBR_SHARE_OUTER bit does
> indeed get coherent pagetable walks working nicely for the coherent
> T620 in the Arm Juno SoC.
> 
> Reviewed-by: Steven Price <[email-masked]>
> Tested-by: Neil Armstrong <[email-masked]>
> Signed-off-by: Robin Murphy <[email-masked]>
> ---
>  drivers/iommu/io-pgtable-arm.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
> index dc7bcf858b6d..b4072a18e45d 100644
> --- a/drivers/iommu/io-pgtable-arm.c
> +++ b/drivers/iommu/io-pgtable-arm.c
> @@ -440,7 +440,13 @@ static arm_lpae_iopte arm_lpae_prot_to_pte(struct arm_lpae_io_pgtable *data,
>  				<< ARM_LPAE_PTE_ATTRINDX_SHIFT);
>  	}
>  
> -	if (prot & IOMMU_CACHE)
> +	/*
> +	 * Also Mali has its own notions of shareability wherein its Inner
> +	 * domain covers the cores within the GPU, and its Outer domain is
> +	 * "outside the GPU" (i.e. either the Inner or System domain in CPU
> +	 * terms, depending on coherency).
> +	 */
> +	if (prot & IOMMU_CACHE && data->iop.fmt != ARM_MALI_LPAE)
>  		pte |= ARM_LPAE_PTE_SH_IS;
>  	else
>  		pte |= ARM_LPAE_PTE_SH_OS;

Actually, it still doesn't work on s922x :-/. For it to work I
correctly, I need to drop the outer shareable flag here.

> @@ -1049,6 +1055,9 @@ 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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