Messages in this thread | | | Date | Wed, 10 Apr 2024 13:10:59 +0530 | Subject | Re: [Query] ACS enablement in the DT based boot flow | From | Vidya Sagar <> |
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Hi folks, any thoughts on this?
On 01-04-2024 16:10, Vidya Sagar wrote: > Hi folks, > ACS (Access Control Services) is configured for a PCI device through pci_enable_acs(). > The first thing pci_enable_acs() checks for is whether the global flag 'pci_acs_enable' is set or not. > The global flag 'pci_acs_enable' is set by the function pci_request_acs(). > > pci_enable_acs() function is called whenever a new PCI device is added to the system > > pci_enable_acs+0x4c/0x2a4 > pci_acs_init+0x38/0x60 > pci_device_add+0x1a0/0x670 > pci_scan_single_device+0xc4/0x100 > pci_scan_slot+0x6c/0x1e0 > pci_scan_child_bus_extend+0x48/0x2e0 > pci_scan_root_bus_bridge+0x64/0xf0 > pci_host_probe+0x18/0xd0 > > In the case of a system that boots using device-tree blob, pci_request_acs() is called when the > device driver binds with the respective device > > of_iommu_configure+0xf4/0x230 > of_dma_configure_id+0x110/0x340 > pci_dma_configure+0x54/0x120 > really_probe+0x80/0x3e0 > __driver_probe_device+0x88/0x1c0 > driver_probe_device+0x3c/0x140 > __device_attach_driver+0xe8/0x1e0 > bus_for_each_drv+0x78/0xf0 > __device_attach+0x104/0x1e0 > device_attach+0x14/0x30 > pci_bus_add_device+0x50/0xd0 > pci_bus_add_devices+0x38/0x90 > pci_host_probe+0x40/0xd0 > > Since the device addition always happens first followed by the driver binding, this flow effectively > makes sure that ACS never gets enabled. > > Ideally, I would expect the pci_request_acs() get called (probably by the OF framework itself) before > calling pci_enable_acs(). > > This happens in the ACPI flow where pci_request_acs() is called during IORT node > initialization (i.e. iort_init_platform_devices() function). > > Is this understanding correct? If yes, would it make sense to call pci_request_acs() during > OF initialization (similar to IORT initialization in ACPI flow)? > > Thanks, > Vidya Sagar
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