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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:02 EST.

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