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SubjectRe: [PATCH] iommu/arm-smmu: request pcie devices to enable ACS
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Wei,
Le 13/06/2016 à 13:18, Robin Murphy a écrit :
> 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.
nit: I would add ", when they get probed."

Besides Reviewed-by: Eric Auger <eric.auger@redhat.com>

Best Regards

Eric
>>
>> 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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>>
>
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