From: Vidya Sagar <vidyas@nvidia.com>
To: "Bjorn Helgaas" <helgaas@kernel.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
"Krzysztof Wilczyński" <kw@linux.com>,
"Lorenzo Pieralisi" <lpieralisi@kernel.org>
Cc: "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Manikanta Maddireddy <mmaddireddy@nvidia.com>,
Shanker Donthineni <sdonthineni@nvidia.com>,
Krishna Thota <kthota@nvidia.com>
Subject: [Query] ACS enablement in the DT based boot flow
Date: Mon, 1 Apr 2024 10:40:15 +0000 [thread overview]
Message-ID: <PH8PR12MB667446D4A4CAD6E0A2F488B5B83F2@PH8PR12MB6674.namprd12.prod.outlook.com> (raw)
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
next reply other threads:[~2024-04-01 10:40 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-01 10:40 Vidya Sagar [this message]
2024-04-10 7:40 ` [Query] ACS enablement in the DT based boot flow Vidya Sagar
2024-04-10 19:28 ` Bjorn Helgaas
2024-04-28 7:23 ` Will Deacon
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