On 19/07/17 12:17, Anup Patel wrote:

On Wed, Jul 19, 2017 at 4:27 PM, Robin Murphy [off-list ref] wrote:

quoted

On 19/07/17 10:33, Anup Patel wrote:

quoted

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.

So does the FlexRM hardware master through the SMMU or not? If it does,
why do you need no-IOMMU mode? If it doesn't, then that's yet another
reason to fix the real problem, which is the utterly broken notion of
there being 'an IOMMU' on the platform 'bus', rather than papering over
it in VFIO.

Robin.

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