linux-kernel - Re: [PATCH 1/5] iommu: Add capability IOMMU_CAP

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Message-ID: <CAALAos_o25mtphxcVE0rr9dE8YAm-os2C_HD9oDnt41ZMDP8pA@mail.gmail.com>
Date:   Wed, 19 Jul 2017 16:49:00 +0530
From:   Anup Patel <anup.patel@...adcom.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Will Deacon <will.deacon@....com>, Joerg Roedel <joro@...tes.org>,
        Baptiste Reynal <b.reynal@...tualopensystems.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Scott Branden <sbranden@...adcom.com>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Linux ARM Kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        kvm@...r.kernel.org,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [PATCH 1/5] iommu: Add capability IOMMU_CAP_BYPASS

On Wed, Jul 19, 2017 at 4:28 PM, Robin Murphy <robin.murphy@....com> wrote:
> On 19/07/17 10:33, Anup Patel wrote:
>> Some of the IOMMUs (such as ARM SMMU) are capable of bypassing
>> transactions for which no IOMMU domain is configured.
>>
>> This patch adds IOMMU_CAP_BYPASS which can be used by IOMMU
>> drivers to advertise transation bypass capability of an IOMMU.
>
> Whatever the intended semantics of this are, I can't help thinking it
> would be better served by allowing callers to explicitly allocate their
> own IOMMU_DOMAIN_IDENTITY domains. That would also be useful for the
> problem we have with legacy virtio devices behind real IOMMUs.

We want to use VFIO no-IOMMU mode for FlexRM device but
currently it does not allow on our SOC because IOMMU ops are
registered for platform bus.

Regards,
Anup