1 =========
2 Bus Types
3 =========
4
5 Definition
6 ~~~~~~~~~~
7 See the kerneldoc for the struct bus_type.
8
9 int bus_register(struct bus_type * bus);
10
11
12 Declaration
13 ~~~~~~~~~~~
14
15 Each bus type in the kernel (PCI, USB, etc) sh
16 object of this type. They must initialize the
17 optionally initialize the match callback::
18
19 struct bus_type pci_bus_type = {
20 .name = "pci",
21 .match = pci_bus_match,
22 };
23
24 The structure should be exported to drivers in
25
26 extern struct bus_type pci_bus_type;
27
28
29 Registration
30 ~~~~~~~~~~~~
31
32 When a bus driver is initialized, it calls bus
33 initializes the rest of the fields in the bus
34 into a global list of bus types. Once the bus
35 the fields in it are usable by the bus driver.
36
37
38 Callbacks
39 ~~~~~~~~~
40
41 match(): Attaching Drivers to Devices
42 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
43
44 The format of device ID structures and the sem
45 them are inherently bus-specific. Drivers typi
46 of device IDs of devices they support that res
47 driver structure.
48
49 The purpose of the match callback is to give t
50 determine if a particular driver supports a pa
51 comparing the device IDs the driver supports w
52 particular device, without sacrificing bus-spe
53 type-safety.
54
55 When a driver is registered with the bus, the
56 iterated over, and the match callback is calle
57 does not have a driver associated with it.
58
59
60
61 Device and Driver Lists
62 ~~~~~~~~~~~~~~~~~~~~~~~
63
64 The lists of devices and drivers are intended
65 lists that many buses keep. They are lists of
66 struct device_drivers, respectively. Bus drive
67 lists as they please, but conversion to the bu
68 necessary.
69
70 The LDM core provides helper functions for ite
71
72 int bus_for_each_dev(struct bus_type * bus,
73 void * data,
74 int (*fn)(struct device
75
76 int bus_for_each_drv(struct bus_type * bus,
77 void * data, int (*fn)(
78
79 These helpers iterate over the respective list
80 for each device or driver in the list. All lis
81 synchronized by taking the bus's lock (read cu
82 count on each object in the list is incremente
83 called; it is decremented after the next objec
84 lock is not held when calling the callback.
85
86
87 sysfs
88 ~~~~~~~~
89 There is a top-level directory named 'bus'.
90
91 Each bus gets a directory in the bus directory
92 directories::
93
94 /sys/bus/pci/
95 |-- devices
96 `-- drivers
97
98 Drivers registered with the bus get a director
99 directory::
100
101 /sys/bus/pci/
102 |-- devices
103 `-- drivers
104 |-- Intel ICH
105 |-- Intel ICH Joystick
106 |-- agpgart
107 `-- e100
108
109 Each device that is discovered on a bus of tha
110 the bus's devices directory to the device's di
111 hierarchy::
112
113 /sys/bus/pci/
114 |-- devices
115 | |-- 00:00.0 -> ../../../root/pci0/
116 | |-- 00:01.0 -> ../../../root/pci0/
117 | `-- 00:02.0 -> ../../../root/pci0/
118 `-- drivers
119
120
121 Exporting Attributes
122 ~~~~~~~~~~~~~~~~~~~~
123
124 ::
125
126 struct bus_attribute {
127 struct attribute attr;
128 ssize_t (*show)(const struct bus_type
129 ssize_t (*store)(const struct bus_type
130 };
131
132 Bus drivers can export attributes using the BU
133 similarly to the DEVICE_ATTR_RW macro for devi
134 definition like this::
135
136 static BUS_ATTR_RW(debug);
137
138 is equivalent to declaring::
139
140 static bus_attribute bus_attr_debug;
141
142 This can then be used to add and remove the at
143 sysfs directory using::
144
145 int bus_create_file(struct bus_type *,
146 void bus_remove_file(struct bus_type *
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.