1PCI with Driver Model
2=====================
3
4How busses are scanned
5----------------------
6
7Any config read will end up at pci_read_config(). This uses
8uclass_get_device_by_seq() to get the PCI bus for a particular bus number.
9Bus number 0 will need to be requested first, and the alias in the device
10tree file will point to the correct device:
11
12
13	aliases {
14		pci0 = &pci;
15	};
16
17	pci: pci-controller {
18		compatible = "sandbox,pci";
19		...
20	};
21
22
23If there is no alias the devices will be numbered sequentially in the device
24tree.
25
26The call to uclass_get_device() will cause the PCI bus to be probed.
27This does a scan of the bus to locate available devices. These devices are
28bound to their appropriate driver if available. If there is no driver, then
29they are bound to a generic PCI driver which does nothing.
30
31After probing a bus, the available devices will appear in the device tree
32under that bus.
33
34Note that this is all done on a lazy basis, as needed, so until something is
35touched on PCI (eg: a call to pci_find_devices()) it will not be probed.
36
37PCI devices can appear in the flattened device tree. If they do this serves to
38specify the driver to use for the device. In this case they will be bound at
39first. Each PCI device node must have a compatible string list as well as a
40<reg> property, as defined by the IEEE Std 1275-1994 PCI bus binding document
41v2.1. Note we must describe PCI devices with the same bus hierarchy as the
42hardware, otherwise driver model cannot detect the correct parent/children
43relationship during PCI bus enumeration thus PCI devices won't be bound to
44their drivers accordingly. A working example like below:
45
46	pci {
47		#address-cells = <3>;
48		#size-cells = <2>;
49		compatible = "pci-x86";
50		u-boot,dm-pre-reloc;
51		ranges = <0x02000000 0x0 0x40000000 0x40000000 0 0x80000000
52			  0x42000000 0x0 0xc0000000 0xc0000000 0 0x20000000
53			  0x01000000 0x0 0x2000 0x2000 0 0xe000>;
54
55		pcie@17,0 {
56			#address-cells = <3>;
57			#size-cells = <2>;
58			compatible = "pci-bridge";
59			u-boot,dm-pre-reloc;
60			reg = <0x0000b800 0x0 0x0 0x0 0x0>;
61
62			topcliff@0,0 {
63				#address-cells = <3>;
64				#size-cells = <2>;
65				compatible = "pci-bridge";
66				u-boot,dm-pre-reloc;
67				reg = <0x00010000 0x0 0x0 0x0 0x0>;
68
69				pciuart0: uart@a,1 {
70					compatible = "pci8086,8811.00",
71							"pci8086,8811",
72							"pciclass,070002",
73							"pciclass,0700",
74							"x86-uart";
75					u-boot,dm-pre-reloc;
76					reg = <0x00025100 0x0 0x0 0x0 0x0
77					       0x01025110 0x0 0x0 0x0 0x0>;
78					......
79				};
80
81				......
82			};
83		};
84
85		......
86	};
87
88In this example, the root PCI bus node is the "/pci" which matches "pci-x86"
89driver. It has a subnode "pcie@17,0" with driver "pci-bridge". "pcie@17,0"
90also has subnode "topcliff@0,0" which is a "pci-bridge" too. Under that bridge,
91a PCI UART device "uart@a,1" is described. This exactly reflects the hardware
92bus hierarchy: on the root PCI bus, there is a PCIe root port which connects
93to a downstream device Topcliff chipset. Inside Topcliff chipset, it has a
94PCIe-to-PCI bridge and all the chipset integrated devices like the PCI UART
95device are on the PCI bus. Like other devices in the device tree, if we want
96to bind PCI devices before relocation, "u-boot,dm-pre-reloc" must be declared
97in each of these nodes.
98
99If PCI devices are not listed in the device tree, U_BOOT_PCI_DEVICE can be used
100to specify the driver to use for the device. The device tree takes precedence
101over U_BOOT_PCI_DEVICE. Plese note with U_BOOT_PCI_DEVICE, only drivers with
102DM_FLAG_PRE_RELOC will be bound before relocation. If neither device tree nor
103U_BOOT_PCI_DEVICE is provided, the built-in driver (either pci_bridge_drv or
104pci_generic_drv) will be used.
105
106
107Sandbox
108-------
109
110With sandbox we need a device emulator for each device on the bus since there
111is no real PCI bus. This works by looking in the device tree node for a
112driver. For example:
113
114
115	pci@1f,0 {
116		compatible = "pci-generic";
117		reg = <0xf800 0 0 0 0>;
118		emul@1f,0 {
119			compatible = "sandbox,swap-case";
120		};
121	};
122
123This means that there is a 'sandbox,swap-case' driver at that bus position.
124Note that the first cell in the 'reg' value is the bus/device/function. See
125PCI_BDF() for the encoding (it is also specified in the IEEE Std 1275-1994
126PCI bus binding document, v2.1)
127
128When this bus is scanned we will end up with something like this:
129
130`- * pci-controller @ 05c660c8, 0
131 `-   pci@1f,0 @ 05c661c8, 63488
132  `-   emul@1f,0 @ 05c662c8
133
134When accesses go to the pci@1f,0 device they are forwarded to its child, the
135emulator.
136