Subject: Re: [PATCH 2/5] iommu/arm-smmu: add IOMMU_CAP_BYPASS to the ARM SMMU
 driver
To: Anup Patel <anup.patel@broadcom.com>,
        Will Deacon <will.deacon@arm.com>, Joerg Roedel <joro@8bytes.org>,
        Baptiste Reynal <b.reynal@virtualopensystems.com>,
        Alex Williamson <alex.williamson@redhat.com>
Cc: Scott Branden <sbranden@broadcom.com>, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, iommu@lists.linux-foundation.org,
        kvm@vger.kernel.org, bcm-kernel-feedback-list@broadcom.com
References: <1500456838-18405-1-git-send-email-anup.patel@broadcom.com>
 <1500456838-18405-3-git-send-email-anup.patel@broadcom.com>
From: Robin Murphy <robin.murphy@arm.com>
Message-ID: <71d21ee4-6112-0ec9-9074-b2a00f5c207c@arm.com>
Date: Wed, 19 Jul 2017 11:59:37 +0100
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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@broadcom.com>
> ---
>  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;
>  	}
>