1
2 Bus Types
3
4 Definition
5 ~~~~~~~~~~
6
7 struct bus_type {
8 char * name;
9
10 struct subsystem subsys;
11 struct kset drivers;
12 struct kset devices;
13
14 struct bus_attribute * bus_attrs;
15 struct device_attribute * dev_attrs;
16 struct driver_attribute * drv_attrs;
17
18 int (*match)(struct device * dev, struct device_driver * drv);
19 int (*hotplug) (struct device *dev, char **envp,
20 int num_envp, char *buffer, int buffer_size);
21 int (*suspend)(struct device * dev, pm_message_t state);
22 int (*resume)(struct device * dev);
23 };
24
25 int bus_register(struct bus_type * bus);
26
27
28 Declaration
29 ~~~~~~~~~~~
30
31 Each bus type in the kernel (PCI, USB, etc) should declare one static
32 object of this type. They must initialize the name field, and may
33 optionally initialize the match callback.
34
35 struct bus_type pci_bus_type = {
36 .name = "pci",
37 .match = pci_bus_match,
38 };
39
40 The structure should be exported to drivers in a header file:
41
42 extern struct bus_type pci_bus_type;
43
44
45 Registration
46 ~~~~~~~~~~~~
47
48 When a bus driver is initialized, it calls bus_register. This
49 initializes the rest of the fields in the bus object and inserts it
50 into a global list of bus types. Once the bus object is registered,
51 the fields in it are usable by the bus driver.
52
53
54 Callbacks
55 ~~~~~~~~~
56
57 match(): Attaching Drivers to Devices
58 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
59
60 The format of device ID structures and the semantics for comparing
61 them are inherently bus-specific. Drivers typically declare an array
62 of device IDs of devices they support that reside in a bus-specific
63 driver structure.
64
65 The purpose of the match callback is provide the bus an opportunity to
66 determine if a particular driver supports a particular device by
67 comparing the device IDs the driver supports with the device ID of a
68 particular device, without sacrificing bus-specific functionality or
69 type-safety.
70
71 When a driver is registered with the bus, the bus's list of devices is
72 iterated over, and the match callback is called for each device that
73 does not have a driver associated with it.
74
75
76
77 Device and Driver Lists
78 ~~~~~~~~~~~~~~~~~~~~~~~
79
80 The lists of devices and drivers are intended to replace the local
81 lists that many buses keep. They are lists of struct devices and
82 struct device_drivers, respectively. Bus drivers are free to use the
83 lists as they please, but conversion to the bus-specific type may be
84 necessary.
85
86 The LDM core provides helper functions for iterating over each list.
87
88 int bus_for_each_dev(struct bus_type * bus, struct device * start, void * data,
89 int (*fn)(struct device *, void *));
90
91 int bus_for_each_drv(struct bus_type * bus, struct device_driver * start,
92 void * data, int (*fn)(struct device_driver *, void *));
93
94 These helpers iterate over the respective list, and call the callback
95 for each device or driver in the list. All list accesses are
96 synchronized by taking the bus's lock (read currently). The reference
97 count on each object in the list is incremented before the callback is
98 called; it is decremented after the next object has been obtained. The
99 lock is not held when calling the callback.
100
101
102 sysfs
103 ~~~~~~~~
104 There is a top-level directory named 'bus'.
105
106 Each bus gets a directory in the bus directory, along with two default
107 directories:
108
109 /sys/bus/pci/
110 |-- devices
111 `-- drivers
112
113 Drivers registered with the bus get a directory in the bus's drivers
114 directory:
115
116 /sys/bus/pci/
117 |-- devices
118 `-- drivers
119 |-- Intel ICH
120 |-- Intel ICH Joystick
121 |-- agpgart
122 `-- e100
123
124 Each device that is discovered on a bus of that type gets a symlink in
125 the bus's devices directory to the device's directory in the physical
126 hierarchy:
127
128 /sys/bus/pci/
129 |-- devices
130 | |-- 00:00.0 -> ../../../root/pci0/00:00.0
131 | |-- 00:01.0 -> ../../../root/pci0/00:01.0
132 | `-- 00:02.0 -> ../../../root/pci0/00:02.0
133 `-- drivers
134
135
136 Exporting Attributes
137 ~~~~~~~~~~~~~~~~~~~~
138 struct bus_attribute {
139 struct attribute attr;
140 ssize_t (*show)(struct bus_type *, char * buf);
141 ssize_t (*store)(struct bus_type *, const char * buf, size_t count);
142 };
143
144 Bus drivers can export attributes using the BUS_ATTR macro that works
145 similarly to the DEVICE_ATTR macro for devices. For example, a definition
146 like this:
147
148 static BUS_ATTR(debug,0644,show_debug,store_debug);
149
150 is equivalent to declaring:
151
152 static bus_attribute bus_attr_debug;
153
154 This can then be used to add and remove the attribute from the bus's
155 sysfs directory using:
156
157 int bus_create_file(struct bus_type *, struct bus_attribute *);
158 void bus_remove_file(struct bus_type *, struct bus_attribute *);
159
160
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