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/Documentation/driver-model/bus.txt

https://bitbucket.org/evzijst/gittest
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  1
  2Bus Types 
  3
  4Definition
  5~~~~~~~~~~
  6
  7struct 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, u32 state);
 22	int		(*resume)(struct device * dev);
 23};
 24
 25int bus_register(struct bus_type * bus);
 26
 27
 28Declaration
 29~~~~~~~~~~~
 30
 31Each bus type in the kernel (PCI, USB, etc) should declare one static
 32object of this type. They must initialize the name field, and may
 33optionally initialize the match callback.
 34
 35struct bus_type pci_bus_type = {
 36       .name	= "pci",
 37       .match	= pci_bus_match,
 38};
 39
 40The structure should be exported to drivers in a header file:
 41
 42extern struct bus_type pci_bus_type;
 43
 44
 45Registration
 46~~~~~~~~~~~~
 47
 48When a bus driver is initialized, it calls bus_register. This
 49initializes the rest of the fields in the bus object and inserts it
 50into a global list of bus types. Once the bus object is registered, 
 51the fields in it are usable by the bus driver. 
 52
 53
 54Callbacks
 55~~~~~~~~~
 56
 57match(): Attaching Drivers to Devices
 58~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 59
 60The format of device ID structures and the semantics for comparing
 61them are inherently bus-specific. Drivers typically declare an array
 62of device IDs of devices they support that reside in a bus-specific
 63driver structure. 
 64
 65The purpose of the match callback is provide the bus an opportunity to
 66determine if a particular driver supports a particular device by
 67comparing the device IDs the driver supports with the device ID of a
 68particular device, without sacrificing bus-specific functionality or
 69type-safety. 
 70
 71When a driver is registered with the bus, the bus's list of devices is
 72iterated over, and the match callback is called for each device that
 73does not have a driver associated with it. 
 74
 75
 76
 77Device and Driver Lists
 78~~~~~~~~~~~~~~~~~~~~~~~
 79
 80The lists of devices and drivers are intended to replace the local
 81lists that many buses keep. They are lists of struct devices and
 82struct device_drivers, respectively. Bus drivers are free to use the
 83lists as they please, but conversion to the bus-specific type may be
 84necessary. 
 85
 86The LDM core provides helper functions for iterating over each list.
 87
 88int bus_for_each_dev(struct bus_type * bus, struct device * start, void * data,
 89		     int (*fn)(struct device *, void *));
 90
 91int bus_for_each_drv(struct bus_type * bus, struct device_driver * start, 
 92		     void * data, int (*fn)(struct device_driver *, void *));
 93
 94These helpers iterate over the respective list, and call the callback
 95for each device or driver in the list. All list accesses are
 96synchronized by taking the bus's lock (read currently). The reference
 97count on each object in the list is incremented before the callback is
 98called; it is decremented after the next object has been obtained. The
 99lock is not held when calling the callback. 
100
101
102sysfs
103~~~~~~~~
104There is a top-level directory named 'bus'.
105
106Each bus gets a directory in the bus directory, along with two default
107directories:
108
109	/sys/bus/pci/
110	|-- devices
111	`-- drivers
112
113Drivers registered with the bus get a directory in the bus's drivers
114directory:
115
116	/sys/bus/pci/
117	|-- devices
118	`-- drivers
119	    |-- Intel ICH
120	    |-- Intel ICH Joystick
121	    |-- agpgart
122	    `-- e100
123
124Each device that is discovered on a bus of that type gets a symlink in
125the bus's devices directory to the device's directory in the physical
126hierarchy:
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
136Exporting Attributes
137~~~~~~~~~~~~~~~~~~~~
138struct 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
144Bus drivers can export attributes using the BUS_ATTR macro that works
145similarly to the DEVICE_ATTR macro for devices. For example, a definition 
146like this:
147
148static BUS_ATTR(debug,0644,show_debug,store_debug);
149
150is equivalent to declaring:
151
152static bus_attribute bus_attr_debug;
153
154This can then be used to add and remove the attribute from the bus's
155sysfs directory using:
156
157int bus_create_file(struct bus_type *, struct bus_attribute *);
158void bus_remove_file(struct bus_type *, struct bus_attribute *);
159
160