1.. SPDX-License-Identifier: GPL-2.0+
2
3PCI with Driver Model
4=====================
5
6How busses are scanned
7----------------------
8
9Any config read will end up at pci_read_config(). This uses
10uclass_get_device_by_seq() to get the PCI bus for a particular bus number.
11Bus number 0 will need to be requested first, and the alias in the device
12tree file will point to the correct device::
13
14	aliases {
15		pci0 = &pcic;
16	};
17
18	pcic: pci@0 {
19		compatible = "sandbox,pci";
20		...
21	};
22
23
24If there is no alias the devices will be numbered sequentially in the device
25tree.
26
27The call to uclass_get_device() will cause the PCI bus to be probed.
28This does a scan of the bus to locate available devices. These devices are
29bound to their appropriate driver if available. If there is no driver, then
30they are bound to a generic PCI driver which does nothing.
31
32After probing a bus, the available devices will appear in the device tree
33under that bus.
34
35Note that this is all done on a lazy basis, as needed, so until something is
36touched on PCI (eg: a call to pci_find_devices()) it will not be probed.
37
38PCI devices can appear in the flattened device tree. If they do, their node
39often contains extra information which cannot be derived from the PCI IDs or
40PCI class of the device. Each PCI device node must have a <reg> property, as
41defined by the IEEE Std 1275-1994 PCI bus binding document v2.1. Compatible
42string list is optional and generally not needed, since PCI is discoverable
43bus, albeit there are justified exceptions. If the compatible string is
44present, matching on it takes precedence over PCI IDs and PCI classes.
45
46Note we must describe PCI devices with the same bus hierarchy as the
47hardware, otherwise driver model cannot detect the correct parent/children
48relationship during PCI bus enumeration thus PCI devices won't be bound to
49their drivers accordingly. A working example like below::
50
51	pci {
52		#address-cells = <3>;
53		#size-cells = <2>;
54		compatible = "pci-x86";
55		u-boot,dm-pre-reloc;
56		ranges = <0x02000000 0x0 0x40000000 0x40000000 0 0x80000000
57			  0x42000000 0x0 0xc0000000 0xc0000000 0 0x20000000
58			  0x01000000 0x0 0x2000 0x2000 0 0xe000>;
59
60		pcie@17,0 {
61			#address-cells = <3>;
62			#size-cells = <2>;
63			compatible = "pci-bridge";
64			u-boot,dm-pre-reloc;
65			reg = <0x0000b800 0x0 0x0 0x0 0x0>;
66
67			topcliff@0,0 {
68				#address-cells = <3>;
69				#size-cells = <2>;
70				compatible = "pci-bridge";
71				u-boot,dm-pre-reloc;
72				reg = <0x00010000 0x0 0x0 0x0 0x0>;
73
74				pciuart0: uart@a,1 {
75					compatible = "pci8086,8811.00",
76							"pci8086,8811",
77							"pciclass,070002",
78							"pciclass,0700",
79							"x86-uart";
80					u-boot,dm-pre-reloc;
81					reg = <0x00025100 0x0 0x0 0x0 0x0
82					       0x01025110 0x0 0x0 0x0 0x0>;
83					......
84				};
85
86				......
87			};
88		};
89
90		......
91	};
92
93In this example, the root PCI bus node is the "/pci" which matches "pci-x86"
94driver. It has a subnode "pcie@17,0" with driver "pci-bridge". "pcie@17,0"
95also has subnode "topcliff@0,0" which is a "pci-bridge" too. Under that bridge,
96a PCI UART device "uart@a,1" is described. This exactly reflects the hardware
97bus hierarchy: on the root PCI bus, there is a PCIe root port which connects
98to a downstream device Topcliff chipset. Inside Topcliff chipset, it has a
99PCIe-to-PCI bridge and all the chipset integrated devices like the PCI UART
100device are on the PCI bus. Like other devices in the device tree, if we want
101to bind PCI devices before relocation, "u-boot,dm-pre-reloc" must be declared
102in each of these nodes.
103
104If PCI devices are not listed in the device tree, U_BOOT_PCI_DEVICE can be used
105to specify the driver to use for the device. The device tree takes precedence
106over U_BOOT_PCI_DEVICE. Please note with U_BOOT_PCI_DEVICE, only drivers with
107DM_FLAG_PRE_RELOC will be bound before relocation. If neither device tree nor
108U_BOOT_PCI_DEVICE is provided, the built-in driver (either pci_bridge_drv or
109pci_generic_drv) will be used.
110
111
112Sandbox
113-------
114
115With sandbox we need a device emulator for each device on the bus since there
116is no real PCI bus. This works by looking in the device tree node for an
117emulator driver. For example::
118
119	pci@1f,0 {
120		compatible = "pci-generic";
121		reg = <0xf800 0 0 0 0>;
122		sandbox,emul = <&emul_1f>;
123	};
124	pci-emul {
125		compatible = "sandbox,pci-emul-parent";
126		emul_1f: emul@1f,0 {
127			compatible = "sandbox,swap-case";
128		};
129	};
130
131This means that there is a 'sandbox,swap-case' driver at that bus position.
132Note that the first cell in the 'reg' value is the bus/device/function. See
133PCI_BDF() for the encoding (it is also specified in the IEEE Std 1275-1994
134PCI bus binding document, v2.1)
135
136The pci-emul node should go outside the pci bus node, since otherwise it will
137be scanned as a PCI device, causing confusion.
138
139When this bus is scanned we will end up with something like this::
140
141   `- * pci@0 @ 05c660c8, 0
142    `-   pci@1f,0 @ 05c661c8, 63488
143   `-   emul@1f,0 @ 05c662c8
144
145When accesses go to the pci@1f,0 device they are forwarded to its emulator.
146
147The sandbox PCI drivers also support dynamic driver binding, allowing device
148driver to declare the driver binding information via U_BOOT_PCI_DEVICE(),
149eliminating the need to provide any device tree node under the host controller
150node. It is required a "sandbox,dev-info" property must be provided in the
151host controller node for this functionality to work.
152
153.. code-block:: none
154
155	pci1: pci@1 {
156		compatible = "sandbox,pci";
157		...
158		sandbox,dev-info = <0x08 0x00 0x1234 0x5678
159				    0x0c 0x00 0x1234 0x5678>;
160	};
161
162The "sandbox,dev-info" property specifies all dynamic PCI devices on this bus.
163Each dynamic PCI device is encoded as 4 cells a group. The first and second
164cells are PCI device number and function number respectively. The third and
165fourth cells are PCI vendor ID and device ID respectively.
166
167When this bus is scanned we will end up with something like this::
168
169 pci        [ + ]   pci_sandbo  |-- pci1
170 pci_emul   [   ]   sandbox_sw  |   |-- sandbox_swap_case_emul
171 pci_emul   [   ]   sandbox_sw  |   `-- sandbox_swap_case_emul
172