linux-kernel - Re: [PATCHv8 1/8] iommu/io-pgtable-arm: Add support to use system cache

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Message-ID: <20201123150616.GB11033@willie-the-truck>
Date:   Mon, 23 Nov 2020 15:06:17 +0000
From:   Will Deacon <will@...nel.org>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Cc:     Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Rob Clark <robdclark@...il.com>,
        Akhil P Oommen <akhilpo@...eaurora.org>,
        freedreno@...ts.freedesktop.org,
        "Kristian H . Kristensen" <hoegsberg@...gle.com>,
        dri-devel@...ts.freedesktop.org, iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCHv8 1/8] iommu/io-pgtable-arm: Add support to use system
 cache

On Tue, Nov 17, 2020 at 08:00:40PM +0530, Sai Prakash Ranjan wrote:
> Add a quirk IO_PGTABLE_QUIRK_ARM_OUTER_WBWA to override
> the attributes set in TCR for the page table walker when
> using system cache.
> 
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
> ---
>  drivers/iommu/io-pgtable-arm.c | 10 ++++++++--
>  include/linux/io-pgtable.h     |  4 ++++
>  2 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
> index a7a9bc08dcd1..7c9ea9d7874a 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_ARM_OUTER_WBWA))
>  		return NULL;
>  
>  	data = arm_lpae_alloc_pgtable(cfg);
> @@ -773,10 +774,15 @@ 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;
> +		if (cfg->quirks & IO_PGTABLE_QUIRK_ARM_OUTER_WBWA)
> +			goto out_free_data;
>  	} else {
>  		tcr->sh = ARM_LPAE_TCR_SH_OS;
>  		tcr->irgn = ARM_LPAE_TCR_RGN_NC;
> -		tcr->orgn = ARM_LPAE_TCR_RGN_NC;
> +		if (!(cfg->quirks & IO_PGTABLE_QUIRK_ARM_OUTER_WBWA))
> +			tcr->orgn = ARM_LPAE_TCR_RGN_NC;
> +		else
> +			tcr->orgn = ARM_LPAE_TCR_RGN_WBWA;
>  	}
>  
>  	tg1 = cfg->quirks & IO_PGTABLE_QUIRK_ARM_TTBR1;
> diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
> index 4cde111e425b..a9a2c59fab37 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_ARM_OUTER_WBWA: Override the attributes set in TCR for
> +	 *	the page table walker when using system cache.

Please can you reword this to say:

  "Override the outer-cacheability attributes set in the TCR for a non-coherent
   page-table walker."

Will