linux-kernel - Re: [PATCH] iommu/arm-smmu: request pcie devices to enable ACS

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Date:	Tue, 14 Jun 2016 09:56:27 +0100
From:	Will Deacon <will.deacon@....com>
To:	Wei Chen <wei.chen@...aro.org>
Cc:	Wei Chen <Wei.Chen@....com>, steve.capper@....com, joro@...tes.org,
	linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
	robin.murphy@....com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] iommu/arm-smmu: request pcie devices to enable ACS

On Tue, Jun 14, 2016 at 11:11:36AM +0800, Wei Chen wrote:
> On 13 June 2016 at 20:45, Will Deacon <will.deacon@....com> wrote:
> > On Mon, Jun 13, 2016 at 05:20:17PM +0800, Wei Chen wrote:
> >> The PCIe ACS capability will affect the layout of iommu groups.
> >> Generally speaking, if the path from root port to the PCIe device
> >> is ACS enabled, the iommu will create a single iommu group for this
> >> PCIe device. If all PCIe devices on the path are ACS enabled then
> >> Linux can determine this path is ACS enabled.
> >>
> >> Linux use two PCIe configuration registers to determine the ACS
> >> status of PCIe devices:
> >> ACS Capability Register and ACS Control Register.
> >>
> >> The first register is used to check the implementation of ACS function
> >> of a PCIe device, the second register is used to check the enable status
> >> of ACS function. If one PCIe device has implemented and enabled the ACS
> >> function then Linux will determine this PCIe device enabled ACS.
> >>
> >> From the Chapter:6.12 of PCI Express Base Specification Revision 3.1a,
> >> we can find that when a PCIe device implements ACS function, the enable
> >> status is set to disabled by default and can be enabled by ACS-aware
> >> software.
> >>
> >> ACS will affect the iommu groups topology, so, the iommu driver is
> >> ACS-aware software. This patch adds a call to pci_request_acs() to the
> >> arm-smmu driver to enable the ACS function in PCIe devices that support
> >> it.
> >>
> >> Signed-off-by: Wei Chen <Wei.Chen@....com>
> >> ---
> >>  drivers/iommu/arm-smmu-v3.c | 2 ++
> >>  drivers/iommu/arm-smmu.c    | 4 +++-
> >>  2 files changed, 5 insertions(+), 1 deletion(-)
> >
> > Thanks, queued for 4.8 w/ Robin and Eric's reviewed-by tags and the minor
> > commit wording change.
> >
> 
> Thanks, I will post a v2 patch to include above changes.

:/ As above, I've already queued this.

Will