Document how pci devices are bound to device drivers.
Signed-off-by: Bin Meng bmeng.cn@gmail.com Acked-by: Simon Glass sjg@chromium.org
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Changes in v4: None Changes in v3: None
doc/driver-model/pci-info.txt | 71 +++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 68 insertions(+), 3 deletions(-)
diff --git a/doc/driver-model/pci-info.txt b/doc/driver-model/pci-info.txt index cf69167..52b4389 100644 --- a/doc/driver-model/pci-info.txt +++ b/doc/driver-model/pci-info.txt @@ -34,9 +34,74 @@ under that bus. Note that this is all done on a lazy basis, as needed, so until something is touched on PCI (eg: a call to pci_find_devices()) it will not be probed.
-PCI devices can appear in the device tree. If they do this serves to specify -the driver to use for the device. In this case they will be bound at -start-up. +PCI devices can appear in the flattened device tree. If they do this serves to +specify the driver to use for the device. In this case they will be bound at +first. Each PCI device node must have a compatible string list as well as a +<reg> property, as defined by the IEEE Std 1275-1994 PCI bus binding document +v2.1. Note we must describe PCI devices with the same bus hierarchy as the +hardware, otherwise driver model cannot detect the correct parent/children +relationship during PCI bus enumeration thus PCI devices won't be bound to +their drivers accordingly. A working example like below: + + pci { + #address-cells = <3>; + #size-cells = <2>; + compatible = "pci-x86"; + u-boot,dm-pre-reloc; + ranges = <0x02000000 0x0 0x40000000 0x40000000 0 0x80000000 + 0x42000000 0x0 0xc0000000 0xc0000000 0 0x20000000 + 0x01000000 0x0 0x2000 0x2000 0 0xe000>; + + pcie@17,0 { + #address-cells = <3>; + #size-cells = <2>; + compatible = "pci-bridge"; + u-boot,dm-pre-reloc; + reg = <0x0000b800 0x0 0x0 0x0 0x0>; + + topcliff@0,0 { + #address-cells = <3>; + #size-cells = <2>; + compatible = "pci-bridge"; + u-boot,dm-pre-reloc; + reg = <0x00010000 0x0 0x0 0x0 0x0>; + + pciuart0: uart@a,1 { + compatible = "pci8086,8811.00", + "pci8086,8811", + "pciclass,070002", + "pciclass,0700", + "x86-uart"; + u-boot,dm-pre-reloc; + reg = <0x00025100 0x0 0x0 0x0 0x0 + 0x01025110 0x0 0x0 0x0 0x0>; + ...... + }; + + ...... + }; + }; + + ...... + }; + +In this example, the root PCI bus node is the "/pci" which matches "pci-x86" +driver. It has a subnode "pcie@17,0" with driver "pci-bridge". "pcie@17,0" +also has subnode "topcliff@0,0" which is a "pci-bridge" too. Under that bridge, +a PCI UART device "uart@a,1" is described. This exactly reflects the hardware +bus hierarchy: on the root PCI bus, there is a PCIe root port which connects +to a downstream device Topcliff chipset. Inside Topcliff chipset, it has a +PCIe-to-PCI bridge and all the chipset integrated devices like the PCI UART +device are on the PCI bus. Like other devices in the device tree, if we want +to bind PCI devices before relocation, "u-boot,dm-pre-reloc" must be declared +in each of these nodes. + +If PCI devices are not listed in the device tree, U_BOOT_PCI_DEVICE can be used +to specify the driver to use for the device. The device tree takes precedence +over U_BOOT_PCI_DEVICE. Plese note with U_BOOT_PCI_DEVICE, only drivers with +DM_FLAG_PRE_RELOC will be bound before relocation. If neither device tree nor +U_BOOT_PCI_DEVICE is provided, the built-in driver (either pci_bridge_drv or +pci_generic_drv) will be used.
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