linux-kernel - Re: [PATCH 0/5] FlexRM support in VFIO platform

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Date:   Wed, 19 Jul 2017 16:47:09 +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 0/5] FlexRM support in VFIO platform

On Wed, Jul 19, 2017 at 4:27 PM, Robin Murphy <robin.murphy@....com> wrote:
> On 19/07/17 10:33, Anup Patel wrote:
>> This patchset primarily adds Broadcom FlexRM reset module for
>> VFIO platform driver. We also have minor improvments in IOMMU
>> and VFIO driver to allow VFIO no-IOMMU mode access to FlexRM.
>
> I'm struggling to understand the IOMMU changes here - what's the
> FlexRM's hardware relationship with the IOMMU, and how is it different
> from any other device? Furthermore, if there *is* a relevant IOMMU
> present, why would no-IOMMU mode need to be involved at all?

We want to have FlexRM device accessible from user-space
using VFIO platform with and without IOMMU.

Currently, if IOMMU ops are available for platform bus then
I cannot access FlexRM device using VFIO no-IOMMU mode.

Since, SMMU can bypass transactions which do not match
any SMRs, we should allow no-IOMMU mode for devices
when IOMMU group is not available.

Regards,
Anup