Re: [PATCHv7 1/7] iommu/io-pgtable-arm: Add support to use system cache

[Will Deacon <will@kernel.org>]

On Fri, Oct 30, 2020 at 02:53:08PM +0530, Sai Prakash Ranjan wrote:
> Add a quirk IO_PGTABLE_QUIRK_SYS_CACHE to override the
> attributes set in TCR for the page table walker when
> using system cache.
> 
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
> ---
>  drivers/iommu/io-pgtable-arm.c | 7 ++++++-
>  include/linux/io-pgtable.h     | 4 ++++
>  2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
> index a7a9bc08dcd1..a356caf1683a 100644
> --- a/drivers/iommu/io-pgtable-arm.c
> +++ b/drivers/iommu/io-pgtable-arm.c
> @@ -761,7 +761,8 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg *cfg, void *cookie)
>  
>  	if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_NS |
>  			    IO_PGTABLE_QUIRK_NON_STRICT |
> -			    IO_PGTABLE_QUIRK_ARM_TTBR1))
> +			    IO_PGTABLE_QUIRK_ARM_TTBR1 |
> +			    IO_PGTABLE_QUIRK_SYS_CACHE))
>  		return NULL;
>  
>  	data = arm_lpae_alloc_pgtable(cfg);
> @@ -773,6 +774,10 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg *cfg, void *cookie)
>  		tcr->sh = ARM_LPAE_TCR_SH_IS;
>  		tcr->irgn = ARM_LPAE_TCR_RGN_WBWA;
>  		tcr->orgn = ARM_LPAE_TCR_RGN_WBWA;
> +	} else if (cfg->quirks & IO_PGTABLE_QUIRK_SYS_CACHE) {
> +		tcr->sh = ARM_LPAE_TCR_SH_OS;
> +		tcr->irgn = ARM_LPAE_TCR_RGN_NC;
> +		tcr->orgn = ARM_LPAE_TCR_RGN_WBWA;

Given that this only applies in the case where then page-table walker is
non-coherent, I think we'd be better off renaming the quirk to something
like IO_PGTABLE_QUIRK_ARM_OUTER_WBWA and then rejecting it in the
non-coherent case.

>  	} else {
>  		tcr->sh = ARM_LPAE_TCR_SH_OS;
>  		tcr->irgn = ARM_LPAE_TCR_RGN_NC;
> diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
> index 4cde111e425b..86631f711e05 100644
> --- a/include/linux/io-pgtable.h
> +++ b/include/linux/io-pgtable.h
> @@ -86,6 +86,9 @@ struct io_pgtable_cfg {
>  	 *
>  	 * IO_PGTABLE_QUIRK_ARM_TTBR1: (ARM LPAE format) Configure the table
>  	 *	for use in the upper half of a split address space.
> +	 *
> +	 * IO_PGTABLE_QUIRK_SYS_CACHE: Override the attributes set in TCR for
> +	 *	the page table walker when using system cache.

and then update this accordingly.

Will