Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 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 to give 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