mirror of
https://github.com/brain-hackers/u-boot-brain
synced 2024-08-29 05:18:51 +09:00
![Bin Meng](/assets/img/avatar_default.png)
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>
136 lines
4.4 KiB
Plaintext
136 lines
4.4 KiB
Plaintext
PCI with Driver Model
|
|
=====================
|
|
|
|
How busses are scanned
|
|
----------------------
|
|
|
|
Any config read will end up at pci_read_config(). This uses
|
|
uclass_get_device_by_seq() to get the PCI bus for a particular bus number.
|
|
Bus number 0 will need to be requested first, and the alias in the device
|
|
tree file will point to the correct device:
|
|
|
|
|
|
aliases {
|
|
pci0 = &pci;
|
|
};
|
|
|
|
pci: pci-controller {
|
|
compatible = "sandbox,pci";
|
|
...
|
|
};
|
|
|
|
|
|
If there is no alias the devices will be numbered sequentially in the device
|
|
tree.
|
|
|
|
The call to uclass_get_device() will cause the PCI bus to be probed.
|
|
This does a scan of the bus to locate available devices. These devices are
|
|
bound to their appropriate driver if available. If there is no driver, then
|
|
they are bound to a generic PCI driver which does nothing.
|
|
|
|
After probing a bus, the available devices will appear in the device tree
|
|
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 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.
|
|
|
|
|
|
Sandbox
|
|
-------
|
|
|
|
With sandbox we need a device emulator for each device on the bus since there
|
|
is no real PCI bus. This works by looking in the device tree node for a
|
|
driver. For example:
|
|
|
|
|
|
pci@1f,0 {
|
|
compatible = "pci-generic";
|
|
reg = <0xf800 0 0 0 0>;
|
|
emul@1f,0 {
|
|
compatible = "sandbox,swap-case";
|
|
};
|
|
};
|
|
|
|
This means that there is a 'sandbox,swap-case' driver at that bus position.
|
|
Note that the first cell in the 'reg' value is the bus/device/function. See
|
|
PCI_BDF() for the encoding (it is also specified in the IEEE Std 1275-1994
|
|
PCI bus binding document, v2.1)
|
|
|
|
When this bus is scanned we will end up with something like this:
|
|
|
|
`- * pci-controller @ 05c660c8, 0
|
|
`- pci@1f,0 @ 05c661c8, 63488
|
|
`- emul@1f,0 @ 05c662c8
|
|
|
|
When accesses go to the pci@1f,0 device they are forwarded to its child, the
|
|
emulator.
|