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dm: pci: Document binding of pci device drivers

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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>
This commit is contained in:
Bin Meng 2015-08-24 01:14:04 -07:00 committed by Simon Glass
parent a1f1582b73
commit f4b5db7c53
1 changed files with 68 additions and 3 deletions
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71
doc/driver-model/pci-info.txt
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@ -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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