linux-kernel - Re: [PATCH] iommu: io-pgtable: Support non-coherent page tables

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Message-ID: <20190618173929.GG4270@fuggles.cambridge.arm.com>
Date:   Tue, 18 Jun 2019 18:39:29 +0100
From:   Will Deacon <will.deacon@....com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Vivek Gautam <vgautam@....qualcomm.com>
Subject: Re: [PATCH] iommu: io-pgtable: Support non-coherent page tables

Hi Bjorn,

On Wed, May 15, 2019 at 04:32:34PM -0700, Bjorn Andersson wrote:
> Describe the memory related to page table walks as non-cachable for iommu
> instances that are not DMA coherent.
> 
> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> ---
>  drivers/iommu/io-pgtable-arm.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
> index 4e21efbc4459..68ff22ffd2cb 100644
> --- a/drivers/iommu/io-pgtable-arm.c
> +++ b/drivers/iommu/io-pgtable-arm.c
> @@ -803,9 +803,15 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg *cfg, void *cookie)
>  		return NULL;
>  
>  	/* TCR */
> -	reg = (ARM_LPAE_TCR_SH_IS << ARM_LPAE_TCR_SH0_SHIFT) |
> -	      (ARM_LPAE_TCR_RGN_WBWA << ARM_LPAE_TCR_IRGN0_SHIFT) |
> -	      (ARM_LPAE_TCR_RGN_WBWA << ARM_LPAE_TCR_ORGN0_SHIFT);
> +	if (cfg->quirks & IO_PGTABLE_QUIRK_NO_DMA) {
> +		reg = (ARM_LPAE_TCR_SH_IS << ARM_LPAE_TCR_SH0_SHIFT) |
> +		      (ARM_LPAE_TCR_RGN_WBWA << ARM_LPAE_TCR_IRGN0_SHIFT) |
> +		      (ARM_LPAE_TCR_RGN_WBWA << ARM_LPAE_TCR_ORGN0_SHIFT);
> +	} else {
> +		reg = (ARM_LPAE_TCR_SH_IS << ARM_LPAE_TCR_SH0_SHIFT) |

Nit: this should be outer-shareable (ARM_LPAE_TCR_SH_OS).

> +		      (ARM_LPAE_TCR_RGN_NC << ARM_LPAE_TCR_IRGN0_SHIFT) |
> +		      (ARM_LPAE_TCR_RGN_NC << ARM_LPAE_TCR_ORGN0_SHIFT);
> +	}

Should we also be doing something similar for the short-descriptor code
in io-pgtable-arm-v7s.c? Looks like you just need to use ARM_V7S_RGN_NC
instead of ARM_V7S_RGN_WBWA when initialising ttbr0 for non-coherent
SMMUs.

Will