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

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Date:	Tue, 14 Jun 2016 10:00:21 +0000
From:	Wei Chen <Wei.Chen@....com>
To:	Will Deacon <Will.Deacon@....com>, Wei Chen <wei.chen@...aro.org>
CC:	Steve Capper <Steve.Capper@....com>,
	"joro@...tes.org" <joro@...tes.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"Robin Murphy" <Robin.Murphy@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH] iommu/arm-smmu: request pcie devices to enable ACS



> -----Original Message-----
> From: Will Deacon [mailto:will.deacon@....com]
> Sent: 2016年6月14日 16:56
> To: Wei Chen
> Cc: Wei Chen; Steve Capper; joro@...tes.org; linux-kernel@...r.kernel.org;
> iommu@...ts.linux-foundation.org; Robin Murphy; 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.
Oh, thank you :)
>
> Will

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