Commit | Line | Data |
---|---|---|
1da177e4 LT |
1 | |
2 | Device Drivers | |
3 | ||
63dc355a | 4 | See the kerneldoc for the struct device_driver. |
1da177e4 LT |
5 | |
6 | ||
7 | Allocation | |
8 | ~~~~~~~~~~ | |
9 | ||
10 | Device drivers are statically allocated structures. Though there may | |
11 | be multiple devices in a system that a driver supports, struct | |
12 | device_driver represents the driver as a whole (not a particular | |
13 | device instance). | |
14 | ||
15 | Initialization | |
16 | ~~~~~~~~~~~~~~ | |
17 | ||
18 | The driver must initialize at least the name and bus fields. It should | |
19 | also initialize the devclass field (when it arrives), so it may obtain | |
20 | the proper linkage internally. It should also initialize as many of | |
21 | the callbacks as possible, though each is optional. | |
22 | ||
23 | Declaration | |
24 | ~~~~~~~~~~~ | |
25 | ||
26 | As stated above, struct device_driver objects are statically | |
27 | allocated. Below is an example declaration of the eepro100 | |
28 | driver. This declaration is hypothetical only; it relies on the driver | |
29 | being converted completely to the new model. | |
30 | ||
31 | static struct device_driver eepro100_driver = { | |
32 | .name = "eepro100", | |
33 | .bus = &pci_bus_type, | |
1da177e4 LT |
34 | |
35 | .probe = eepro100_probe, | |
36 | .remove = eepro100_remove, | |
37 | .suspend = eepro100_suspend, | |
38 | .resume = eepro100_resume, | |
39 | }; | |
40 | ||
41 | Most drivers will not be able to be converted completely to the new | |
42 | model because the bus they belong to has a bus-specific structure with | |
43 | bus-specific fields that cannot be generalized. | |
44 | ||
45 | The most common example of this are device ID structures. A driver | |
46 | typically defines an array of device IDs that it supports. The format | |
47 | of these structures and the semantics for comparing device IDs are | |
48 | completely bus-specific. Defining them as bus-specific entities would | |
49 | sacrifice type-safety, so we keep bus-specific structures around. | |
50 | ||
51 | Bus-specific drivers should include a generic struct device_driver in | |
52 | the definition of the bus-specific driver. Like this: | |
53 | ||
54 | struct pci_driver { | |
55 | const struct pci_device_id *id_table; | |
56 | struct device_driver driver; | |
57 | }; | |
58 | ||
59 | A definition that included bus-specific fields would look like | |
60 | (using the eepro100 driver again): | |
61 | ||
62 | static struct pci_driver eepro100_driver = { | |
63 | .id_table = eepro100_pci_tbl, | |
64 | .driver = { | |
65 | .name = "eepro100", | |
66 | .bus = &pci_bus_type, | |
1da177e4 LT |
67 | .probe = eepro100_probe, |
68 | .remove = eepro100_remove, | |
69 | .suspend = eepro100_suspend, | |
70 | .resume = eepro100_resume, | |
71 | }, | |
72 | }; | |
73 | ||
74 | Some may find the syntax of embedded struct initialization awkward or | |
75 | even a bit ugly. So far, it's the best way we've found to do what we want... | |
76 | ||
77 | Registration | |
78 | ~~~~~~~~~~~~ | |
79 | ||
80 | int driver_register(struct device_driver * drv); | |
81 | ||
82 | The driver registers the structure on startup. For drivers that have | |
83 | no bus-specific fields (i.e. don't have a bus-specific driver | |
84 | structure), they would use driver_register and pass a pointer to their | |
85 | struct device_driver object. | |
86 | ||
87 | Most drivers, however, will have a bus-specific structure and will | |
88 | need to register with the bus using something like pci_driver_register. | |
89 | ||
90 | It is important that drivers register their driver structure as early as | |
91 | possible. Registration with the core initializes several fields in the | |
92 | struct device_driver object, including the reference count and the | |
93 | lock. These fields are assumed to be valid at all times and may be | |
94 | used by the device model core or the bus driver. | |
95 | ||
96 | ||
97 | Transition Bus Drivers | |
98 | ~~~~~~~~~~~~~~~~~~~~~~ | |
99 | ||
100 | By defining wrapper functions, the transition to the new model can be | |
101 | made easier. Drivers can ignore the generic structure altogether and | |
102 | let the bus wrapper fill in the fields. For the callbacks, the bus can | |
103 | define generic callbacks that forward the call to the bus-specific | |
104 | callbacks of the drivers. | |
105 | ||
106 | This solution is intended to be only temporary. In order to get class | |
107 | information in the driver, the drivers must be modified anyway. Since | |
108 | converting drivers to the new model should reduce some infrastructural | |
109 | complexity and code size, it is recommended that they are converted as | |
110 | class information is added. | |
111 | ||
112 | Access | |
113 | ~~~~~~ | |
114 | ||
115 | Once the object has been registered, it may access the common fields of | |
116 | the object, like the lock and the list of devices. | |
117 | ||
118 | int driver_for_each_dev(struct device_driver * drv, void * data, | |
119 | int (*callback)(struct device * dev, void * data)); | |
120 | ||
121 | The devices field is a list of all the devices that have been bound to | |
122 | the driver. The LDM core provides a helper function to operate on all | |
123 | the devices a driver controls. This helper locks the driver on each | |
124 | node access, and does proper reference counting on each device as it | |
125 | accesses it. | |
126 | ||
127 | ||
128 | sysfs | |
129 | ~~~~~ | |
130 | ||
131 | When a driver is registered, a sysfs directory is created in its | |
132 | bus's directory. In this directory, the driver can export an interface | |
133 | to userspace to control operation of the driver on a global basis; | |
134 | e.g. toggling debugging output in the driver. | |
135 | ||
136 | A future feature of this directory will be a 'devices' directory. This | |
137 | directory will contain symlinks to the directories of devices it | |
138 | supports. | |
139 | ||
140 | ||
141 | ||
142 | Callbacks | |
143 | ~~~~~~~~~ | |
144 | ||
145 | int (*probe) (struct device * dev); | |
146 | ||
4109aca0 DB |
147 | The probe() entry is called in task context, with the bus's rwsem locked |
148 | and the driver partially bound to the device. Drivers commonly use | |
149 | container_of() to convert "dev" to a bus-specific type, both in probe() | |
150 | and other routines. That type often provides device resource data, such | |
151 | as pci_dev.resource[] or platform_device.resources, which is used in | |
152 | addition to dev->platform_data to initialize the driver. | |
153 | ||
154 | This callback holds the driver-specific logic to bind the driver to a | |
155 | given device. That includes verifying that the device is present, that | |
156 | it's a version the driver can handle, that driver data structures can | |
157 | be allocated and initialized, and that any hardware can be initialized. | |
158 | Drivers often store a pointer to their state with dev_set_drvdata(). | |
159 | When the driver has successfully bound itself to that device, then probe() | |
160 | returns zero and the driver model code will finish its part of binding | |
161 | the driver to that device. | |
162 | ||
163 | A driver's probe() may return a negative errno value to indicate that | |
164 | the driver did not bind to this device, in which case it should have | |
d6bc8ac9 | 165 | released all resources it allocated. |
1da177e4 LT |
166 | |
167 | int (*remove) (struct device * dev); | |
168 | ||
4109aca0 | 169 | remove is called to unbind a driver from a device. This may be |
1da177e4 | 170 | called if a device is physically removed from the system, if the |
4109aca0 DB |
171 | driver module is being unloaded, during a reboot sequence, or |
172 | in other cases. | |
1da177e4 LT |
173 | |
174 | It is up to the driver to determine if the device is present or | |
175 | not. It should free any resources allocated specifically for the | |
176 | device; i.e. anything in the device's driver_data field. | |
177 | ||
178 | If the device is still present, it should quiesce the device and place | |
179 | it into a supported low-power state. | |
180 | ||
1a222bca | 181 | int (*suspend) (struct device * dev, pm_message_t state); |
1da177e4 | 182 | |
9480e307 | 183 | suspend is called to put the device in a low power state. |
1da177e4 | 184 | |
1a222bca | 185 | int (*resume) (struct device * dev); |
1da177e4 | 186 | |
9480e307 | 187 | Resume is used to bring a device back from a low power state. |
1da177e4 LT |
188 | |
189 | ||
190 | Attributes | |
191 | ~~~~~~~~~~ | |
192 | struct driver_attribute { | |
193 | struct attribute attr; | |
909662e1 | 194 | ssize_t (*show)(struct device_driver *driver, char *buf); |
195 | ssize_t (*store)(struct device_driver *, const char * buf, size_t count); | |
1da177e4 LT |
196 | }; |
197 | ||
198 | Device drivers can export attributes via their sysfs directories. | |
199 | Drivers can declare attributes using a DRIVER_ATTR macro that works | |
200 | identically to the DEVICE_ATTR macro. | |
201 | ||
202 | Example: | |
203 | ||
204 | DRIVER_ATTR(debug,0644,show_debug,store_debug); | |
205 | ||
206 | This is equivalent to declaring: | |
207 | ||
208 | struct driver_attribute driver_attr_debug; | |
209 | ||
210 | This can then be used to add and remove the attribute from the | |
211 | driver's directory using: | |
212 | ||
099c2f21 PC |
213 | int driver_create_file(struct device_driver *, const struct driver_attribute *); |
214 | void driver_remove_file(struct device_driver *, const struct driver_attribute *); |