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Bin Mengb5986482019-07-18 00:33:56 -07001.. SPDX-License-Identifier: GPL-2.0+
2
Simon Glassff3e0772015-03-05 12:25:25 -07003PCI 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.
Bin Meng947eb432015-07-27 00:33:43 -070011Bus number 0 will need to be requested first, and the alias in the device
Bin Mengb5986482019-07-18 00:33:56 -070012tree file will point to the correct device::
Simon Glassff3e0772015-03-05 12:25:25 -070013
14 aliases {
Tom Rini42c64d12020-02-11 12:41:23 -050015 pci0 = &pcic;
Simon Glassff3e0772015-03-05 12:25:25 -070016 };
17
Tom Rini42c64d12020-02-11 12:41:23 -050018 pcic: pci@0 {
Simon Glassff3e0772015-03-05 12:25:25 -070019 compatible = "sandbox,pci";
20 ...
21 };
22
23
24If there is no alias the devices will be numbered sequentially in the device
25tree.
26
Bin Meng947eb432015-07-27 00:33:43 -070027The call to uclass_get_device() will cause the PCI bus to be probed.
Simon Glassff3e0772015-03-05 12:25:25 -070028This 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
Bin Meng947eb432015-07-27 00:33:43 -070036touched on PCI (eg: a call to pci_find_devices()) it will not be probed.
Simon Glassff3e0772015-03-05 12:25:25 -070037
Marek Vasut92ed9862018-10-10 21:27:07 +020038PCI 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
Bin Mengf4b5db72015-08-24 01:14:04 -070047hardware, otherwise driver model cannot detect the correct parent/children
48relationship during PCI bus enumeration thus PCI devices won't be bound to
Bin Mengb5986482019-07-18 00:33:56 -070049their drivers accordingly. A working example like below::
Bin Mengf4b5db72015-08-24 01:14:04 -070050
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
Simon Glassbdaa9762019-09-25 08:56:14 -0600106over U_BOOT_PCI_DEVICE. Please note with U_BOOT_PCI_DEVICE, only drivers with
Bin Mengf4b5db72015-08-24 01:14:04 -0700107DM_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.
Simon Glassff3e0772015-03-05 12:25:25 -0700110
111
112Sandbox
113-------
114
115With sandbox we need a device emulator for each device on the bus since there
Simon Glass9b69ba42019-09-25 08:56:10 -0600116is no real PCI bus. This works by looking in the device tree node for an
117emulator driver. For example::
Simon Glassff3e0772015-03-05 12:25:25 -0700118
119 pci@1f,0 {
120 compatible = "pci-generic";
121 reg = <0xf800 0 0 0 0>;
Simon Glass9b69ba42019-09-25 08:56:10 -0600122 sandbox,emul = <&emul_1f>;
123 };
124 pci-emul {
125 compatible = "sandbox,pci-emul-parent";
126 emul_1f: emul@1f,0 {
Simon Glassff3e0772015-03-05 12:25:25 -0700127 compatible = "sandbox,swap-case";
Simon Glass23f40a32021-02-03 06:01:16 -0700128 #emul-cells = <0>;
Simon Glassff3e0772015-03-05 12:25:25 -0700129 };
130 };
131
132This means that there is a 'sandbox,swap-case' driver at that bus position.
133Note that the first cell in the 'reg' value is the bus/device/function. See
134PCI_BDF() for the encoding (it is also specified in the IEEE Std 1275-1994
135PCI bus binding document, v2.1)
136
Simon Glass9b69ba42019-09-25 08:56:10 -0600137The pci-emul node should go outside the pci bus node, since otherwise it will
138be scanned as a PCI device, causing confusion.
139
Bin Mengb5986482019-07-18 00:33:56 -0700140When this bus is scanned we will end up with something like this::
Simon Glassff3e0772015-03-05 12:25:25 -0700141
Tom Rini42c64d12020-02-11 12:41:23 -0500142 `- * pci@0 @ 05c660c8, 0
Bin Mengb5986482019-07-18 00:33:56 -0700143 `- pci@1f,0 @ 05c661c8, 63488
Simon Glass9b69ba42019-09-25 08:56:10 -0600144 `- emul@1f,0 @ 05c662c8
Simon Glassff3e0772015-03-05 12:25:25 -0700145
Simon Glass9b69ba42019-09-25 08:56:10 -0600146When accesses go to the pci@1f,0 device they are forwarded to its emulator.
Bin Meng43459982018-08-03 01:14:45 -0700147
148The sandbox PCI drivers also support dynamic driver binding, allowing device
149driver to declare the driver binding information via U_BOOT_PCI_DEVICE(),
150eliminating the need to provide any device tree node under the host controller
151node. It is required a "sandbox,dev-info" property must be provided in the
152host controller node for this functionality to work.
153
Bin Mengb5986482019-07-18 00:33:56 -0700154.. code-block:: none
155
Tom Rini42c64d12020-02-11 12:41:23 -0500156 pci1: pci@1 {
Bin Meng43459982018-08-03 01:14:45 -0700157 compatible = "sandbox,pci";
158 ...
159 sandbox,dev-info = <0x08 0x00 0x1234 0x5678
160 0x0c 0x00 0x1234 0x5678>;
161 };
162
163The "sandbox,dev-info" property specifies all dynamic PCI devices on this bus.
164Each dynamic PCI device is encoded as 4 cells a group. The first and second
165cells are PCI device number and function number respectively. The third and
166fourth cells are PCI vendor ID and device ID respectively.
167
Bin Mengb5986482019-07-18 00:33:56 -0700168When this bus is scanned we will end up with something like this::
Bin Meng43459982018-08-03 01:14:45 -0700169
Tom Rini42c64d12020-02-11 12:41:23 -0500170 pci [ + ] pci_sandbo |-- pci1
Bin Meng43459982018-08-03 01:14:45 -0700171 pci_emul [ ] sandbox_sw | |-- sandbox_swap_case_emul
172 pci_emul [ ] sandbox_sw | `-- sandbox_swap_case_emul