Re: [PATCH 2/5] iommu/arm-smmu: add IOMMU_CAP_BYPASS to the ARM SMMU driver

[Robin Murphy]

On 19/07/17 10:33, Anup Patel wrote:
> The ARM SMMUv1 and SMMUv2 support bypassing transactions for
> which domain is not configured. The patch adds corresponding
> IOMMU capability to advertise this fact.
> 
> Signed-off-by: Anup Patel <anup.patel@xxxxxxxxxxxx>
> ---
>  drivers/iommu/arm-smmu.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index bc89b4d..08a9020 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -1483,6 +1483,8 @@ static bool arm_smmu_capable(enum iommu_cap cap)
>  		return true;
>  	case IOMMU_CAP_NOEXEC:
>  		return true;
> +	case IOMMU_CAP_BYPASS:
> +		return true;

Except when it isn't, of course.

Beware that what we'd like to do in the long term is flip the polarity
of disable_bypass, because there isn't generally a good reason for
Non-Secure DMA to be happening behind Linux's back.

Robin.

>  	default:
>  		return false;
>  	}
>