[Question] PCI ACS is broken for ARM SMMU v3?

[lorenzo.pieralisi@arm.com (Lorenzo Pieralisi)]

On Tue, Sep 05, 2017 at 08:47:15PM +0800, Zhou Wang wrote:
> On 2017/9/4 23:59, Lorenzo Pieralisi wrote:
> > On Mon, Sep 04, 2017 at 08:33:22PM +0800, Zhou Wang wrote:
> >> +to: Lorenzo
> >>
> >> On 2017/8/31 22:21, Zhou Wang wrote:
> >>> Hi Will and Alex,
> >>>
> >>> pci_request_acs is called in drivers/iommu/arm-smmu-v3.c to set pci_acs_enable.
> >>>
> >>> PCI subsystem tries to enable ACS as below:
> >>>
> >>> 	pci_device_add
> >>> 		--> pci_init_capabilities
> >>> 			--> pci_enable_acs
> >>>
> >>> in ACPI PCI driver. However, ACPI PCI driver will be called before SMMU v3 driver,
> >>> which will lead pci_enable_acs to return directly as pci_acs_enable is not set
> >>> before SMMU v3 driver loading.
> >>>
> >>> I think this is a bug, what do you think about this problem?
> > 
> > I think that it is a bug that affects OF/ACPI alike. One way of solving
> 
> Yes, DT also has this problem.
> 
> > it is requesting ACS at IORT init following appropriate checks (ie
> > mappings PCI->IOMMU - that would not solve the OF path though). I can
> > put together a quick fix, the overall problem needs some thinking
> > though.
> 
> I am not familiar with IORT init, but can we do it like:
> 
> diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
> index a3215ee..a6f1a21 100644
> --- a/drivers/acpi/arm64/iort.c
> +++ b/drivers/acpi/arm64/iort.c
> @@ -1131,6 +1131,7 @@ static void __init iort_init_platform_devices(void)
> 				acpi_free_fwnode_static(fwnode);
> 				return;
> 			}
> + 			pci_request_acs();
> 		}
> 
> 		iort_node = ACPI_ADD_PTR(struct acpi_iort_node, iort_node,
> 

Yep, will send something similar shortly.

Thanks,
Lorenzo