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SubjectRe: [PATCH] iommu/arm-smmu: request pcie devices to enable ACS
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On 13/06/16 10:20, 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@arm.com>

Makes sense to me:

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

p.s. The confidential disclaimer is a good way to get patches ignored
here on the lists - please check with Steve about getting set up on the
appropriate SMTP server.

Robin.

> ---
> drivers/iommu/arm-smmu-v3.c | 2 ++
> drivers/iommu/arm-smmu.c | 4 +++-
> 2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index 94b6821..30ea899 100644
> --- a/drivers/iommu/arm-smmu-v3.c
> +++ b/drivers/iommu/arm-smmu-v3.c
> @@ -2686,6 +2686,8 @@ static int __init arm_smmu_init(void)
> if (ret)
> return ret;
>
> + pci_request_acs();
> +
> return bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
> }
>
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 9345a3f..ab365ec 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -2096,8 +2096,10 @@ static int __init arm_smmu_init(void)
> #endif
>
> #ifdef CONFIG_PCI
> - if (!iommu_present(&pci_bus_type))
> + if (!iommu_present(&pci_bus_type)) {
> + pci_request_acs();
> bus_set_iommu(&pci_bus_type, &arm_smmu_ops);
> + }
> #endif
>
> return 0;
> --
> 2.7.4
>
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>
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