linux-kernel - Re: [PATCH 5/7] iommu/arm-smmu: Support DOMAIN_ATTR_SPLIT

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Message-ID: <20190917172020.hpv5qqdpihvqkehp@willie-the-truck>
Date:   Tue, 17 Sep 2019 18:20:20 +0100
From:   Will Deacon <will@...nel.org>
To:     Jordan Crouse <jcrouse@...eaurora.org>
Cc:     freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 5/7] iommu/arm-smmu: Support DOMAIN_ATTR_SPLIT_TABLES

On Tue, Aug 20, 2019 at 01:06:30PM -0600, Jordan Crouse wrote:
> Support the DOMAIN_ATTR_SPLIT_TABLES attribute to let the leaf driver
> know if split pagetables are enabled for the domain.
> 
> Signed-off-by: Jordan Crouse <jcrouse@...eaurora.org>
> ---
> 
>  drivers/iommu/arm-smmu.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 3f41cf7..6a512ff 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -1442,6 +1442,9 @@ static int arm_smmu_domain_get_attr(struct iommu_domain *domain,
>  		case DOMAIN_ATTR_NESTING:
>  			*(int *)data = (smmu_domain->stage == ARM_SMMU_DOMAIN_NESTED);
>  			return 0;
> +		case DOMAIN_ATTR_SPLIT_TABLES:
> +			*(int *)data = !!(smmu_domain->split_pagetables);
> +			return 0;

Hmm. Could you move the setting of this attribute into
arm_smmu_domain_set_attr() and reject it if the ias != 48 in there? That way
the user of the domain can request this feature, rather than us enforcing it
based on the compatible string.

I'd also prefer to call it DOMAIN_ATTR_USE_TTBR1 instead, since it's pretty
ARM specific at this point.

Will