Subject: [PATCH] iommu/arm-smmu: Don't allocate resources for bypass domains

From: [email-masked] (Will Deacon)
Date: Fri, 15 Apr 2016 14:05:21 +0100

On Wed, Apr 13, 2016 at 03:46:57PM +0100, Robin Murphy wrote:
> Until we get fully plumbed into of_iommu_configure, our default
> IOMMU_DOMAIN_DMA domains just bypass translation. Since we achieve that
> by leaving the stream table entries set to bypass instead of pointing at
> a translation context, the context bank we allocate for the domain is
> completely wasted. Context banks are typically a rather limited
> resource, so don't hog ones we don't need.

Eric, does this resolve your remaining passthrough regressions when applied
on top of my patch?

Will

> Reported-by: Eric Auger <[email-masked]>
> Signed-off-by: Robin Murphy <[email-masked]>
> ---
>  drivers/iommu/arm-smmu.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 5158feb..7c39ac4 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -826,6 +826,12 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
>  	if (smmu_domain->smmu)
>  		goto out_unlock;
>  
> +	/* We're bypassing these SIDs, so don't allocate an actual context */
> +	if (domain->type == IOMMU_DOMAIN_DMA) {
> +		smmu_domain->smmu = smmu;
> +		goto out_unlock;
> +	}
> +
>  	/*
>  	 * Mapping the requested stage onto what we support is surprisingly
>  	 * complicated, mainly because the spec allows S1+S2 SMMUs without
> @@ -948,7 +954,7 @@ static void arm_smmu_destroy_domain_context(struct iommu_domain *domain)
>  	void __iomem *cb_base;
>  	int irq;
>  
> -	if (!smmu)
> +	if (!smmu || domain->type == IOMMU_DOMAIN_DMA)
>  		return;
>  
>  	/*
> -- 
> 2.7.3.dirty
>