[+cc Will, Joerg]
On Mon, Apr 01, 2024 at 10:40:15AM +0000, 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)?
Your understanding looks correct to me. My call graph notes, FWIW:
mem_init
pci_iommu_alloc # x86 only
amd_iommu_detect # init_state = IOMMU_START_STATE
iommu_go_to_state(IOMMU_IVRS_DETECTED)
state_next
switch (init_state)
case IOMMU_START_STATE:
detect_ivrs
pci_request_acs
pci_acs_enable = 1 # <--
detect_intel_iommu
pci_request_acs
pci_acs_enable = 1 # <--
pci_scan_single_device # PCI enumeration
...
pci_init_capabilities
pci_acs_init
pci_enable_acs
if (pci_acs_enable) # <--
pci_std_enable_acs
__driver_probe_device
really_probe
pci_dma_configure # pci_bus_type.dma_configure
if (OF)
of_dma_configure
of_dma_configure_id
of_iommu_configure
pci_request_acs # <-- 6bf6c24720d3
iommu_probe_device
else if (ACPI)
acpi_dma_configure
acpi_dma_configure_id
acpi_iommu_configure_id
iommu_probe_device
The pci_request_acs() in of_iommu_configure(), which happens too late
to affect pci_enable_acs(), was added by 6bf6c24720d3 ("iommu/of:
Request ACS from the PCI core when configuring IOMMU linkage"), so I
cc'd Will and Joerg. I don't know if that *used* to work and got
broken somehow, or if it never worked as intended.
Bjorn
