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

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Message-ID: <20160613124531.GE1605@arm.com>
Date:	Mon, 13 Jun 2016 13:45:32 +0100
From:	Will Deacon <will.deacon@....com>
To:	Wei Chen <Wei.Chen@....com>
Cc:	linux-arm-kernel@...ts.infradead.org,
	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	robin.murphy@....com, joro@...tes.org, steve.capper@....com
Subject: Re: [PATCH] iommu/arm-smmu: request pcie devices to enable ACS

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.

Will