Subject: [PATCH] iommu/arm-smmu: request pcie devices to enable ACS

From: [email-masked] (Robin Murphy)
Date: Mon, 13 Jun 2016 12:18:50 +0100

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 <[email-masked]>

Makes sense to me:

Reviewed-by: Robin Murphy <[email-masked]>

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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