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

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Date:	Tue, 14 Jun 2016 11:11:36 +0800
From:	Wei Chen <wei.chen@...aro.org>
To:	Will Deacon <will.deacon@....com>
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 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.

> Will
>
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> linux-arm-kernel@...ts.infradead.org
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