1 ===============================
2 Creating an input device driver
3 ===============================
4
5 The simplest example
6 ~~~~~~~~~~~~~~~~~~~~
7
8 Here comes a very simple example of an input d
9 just one button and the button is accessible a
10 pressed or released a BUTTON_IRQ happens. The
11
12 #include <linux/input.h>
13 #include <linux/module.h>
14 #include <linux/init.h>
15
16 #include <asm/irq.h>
17 #include <asm/io.h>
18
19 static struct input_dev *button_dev;
20
21 static irqreturn_t button_interrupt(int ir
22 {
23 input_report_key(button_dev, BTN_0
24 input_sync(button_dev);
25 return IRQ_HANDLED;
26 }
27
28 static int __init button_init(void)
29 {
30 int error;
31
32 if (request_irq(BUTTON_IRQ, button
33 printk(KERN_ERR "button.c:
34 return -EBUSY;
35 }
36
37 button_dev = input_allocate_device
38 if (!button_dev) {
39 printk(KERN_ERR "button.c:
40 error = -ENOMEM;
41 goto err_free_irq;
42 }
43
44 button_dev->evbit[0] = BIT_MASK(EV
45 button_dev->keybit[BIT_WORD(BTN_0)
46
47 error = input_register_device(butt
48 if (error) {
49 printk(KERN_ERR "button.c:
50 goto err_free_dev;
51 }
52
53 return 0;
54
55 err_free_dev:
56 input_free_device(button_dev);
57 err_free_irq:
58 free_irq(BUTTON_IRQ, button_interr
59 return error;
60 }
61
62 static void __exit button_exit(void)
63 {
64 input_unregister_device(button_dev
65 free_irq(BUTTON_IRQ, button_interr
66 }
67
68 module_init(button_init);
69 module_exit(button_exit);
70
71 What the example does
72 ~~~~~~~~~~~~~~~~~~~~~
73
74 First it has to include the <linux/input.h> fi
75 input subsystem. This provides all the definit
76
77 In the _init function, which is called either
78 booting the kernel, it grabs the required reso
79 for the presence of the device).
80
81 Then it allocates a new input device structure
82 and sets up input bitfields. This way the devi
83 parts of the input systems what it is - what e
84 accepted by this input device. Our example dev
85 type events, and from those only BTN_0 event c
86 two bits. We could have used::
87
88 set_bit(EV_KEY, button_dev->evbit);
89 set_bit(BTN_0, button_dev->keybit);
90
91 as well, but with more than single bits the fi
92 shorter.
93
94 Then the example driver registers the input de
95
96 input_register_device(button_dev);
97
98 This adds the button_dev structure to linked l
99 calls device handler modules _connect function
100 device has appeared. input_register_device() m
101 not be called from an interrupt or with a spin
102
103 While in use, the only used function of the dr
104
105 button_interrupt()
106
107 which upon every interrupt from the button che
108 via the::
109
110 input_report_key()
111
112 call to the input system. There is no need to
113 routine isn't reporting two same value events
114 the input system, because the input_report_* f
115 themselves.
116
117 Then there is the::
118
119 input_sync()
120
121 call to tell those who receive the events that
122 This doesn't seem important in the one button
123 for example for mouse movement, where you don'
124 to be interpreted separately, because that'd r
125
126 dev->open() and dev->close()
127 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
128
129 In case the driver has to repeatedly poll the
130 have an interrupt coming from it and the polli
131 all the time, or if the device uses a valuable
132 can use the open and close callback to know wh
133 release the interrupt and when it must resume
134 again. To do that, we would add this to our ex
135
136 static int button_open(struct input_dev *d
137 {
138 if (request_irq(BUTTON_IRQ, button
139 printk(KERN_ERR "button.c:
140 return -EBUSY;
141 }
142
143 return 0;
144 }
145
146 static void button_close(struct input_dev
147 {
148 free_irq(IRQ_AMIGA_VERTB, button_i
149 }
150
151 static int __init button_init(void)
152 {
153 ...
154 button_dev->open = button_open;
155 button_dev->close = button_close;
156 ...
157 }
158
159 Note that input core keeps track of number of
160 makes sure that dev->open() is called only whe
161 to the device and that dev->close() is called
162 disconnects. Calls to both callbacks are seria
163
164 The open() callback should return a 0 in case
165 in case of failure. The close() callback (whic
166
167 Inhibiting input devices
168 ~~~~~~~~~~~~~~~~~~~~~~~~
169
170 Inhibiting a device means ignoring input event
171 maintaining relationships with input handlers
172 relationships, or relationships to be establis
173 inhibited state.
174
175 If a device is inhibited, no input handler wil
176
177 The fact that nobody wants events from the dev
178 calling device's close() (if there are users)
179 inhibit and uninhibit operations, respectively
180 is to stop providing events to the input core
181 providing events to the input core.
182
183 Calling the device's close() method on inhibit
184 driver to save power. Either by directly power
185 releasing the runtime-PM reference it got in o
186 runtime-PM.
187
188 Inhibiting and uninhibiting are orthogonal to
189 input handlers. Userspace might want to inhibi
190 any handler is positively matched against it.
191
192 Inhibiting and uninhibiting are orthogonal to
193 too. Being a wakeup source plays a role when t
194 the system is operating. How drivers should p
195 inhibiting, sleeping and being a wakeup source
196
197 Taking the analogy with the network devices -
198 doesn't mean that it should be impossible be w
199 this interface. So, there may be input drivers
200 sources even when inhibited. Actually, in many
201 is declared a wakeup interrupt and its handlin
202 is not aware of input-specific inhibit (nor sh
203 containing several interfaces can be inhibited
204 inhibiting one interface shouldn't affect the
205 wakeup source.
206
207 If a device is to be considered a wakeup sourc
208 must be taken when programming its suspend(),
209 open(). Depending on what close() means for th
210 opening() it before going to sleep might make
211 wakeup events. The device is going to sleep an
212
213 Basic event types
214 ~~~~~~~~~~~~~~~~~
215
216 The most simple event type is EV_KEY, which is
217 It's reported to the input system via::
218
219 input_report_key(struct input_dev *dev
220
221 See uapi/linux/input-event-codes.h for the all
222 KEY_MAX). Value is interpreted as a truth valu
223 key pressed, zero value means key released. Th
224 in case the value is different from before.
225
226 In addition to EV_KEY, there are two more basi
227 EV_ABS. They are used for relative and absolut
228 device. A relative value may be for example a
229 The mouse reports it as a relative difference
230 because it doesn't have any absolute coordinat
231 events are namely for joysticks and digitizers
232 absolute coordinate systems.
233
234 Having the device report EV_REL buttons is as
235 set the corresponding bits and call the::
236
237 input_report_rel(struct input_dev *dev
238
239 function. Events are generated only for non-ze
240
241 However EV_ABS requires a little special care.
242 input_register_device, you have to fill additi
243 struct for each absolute axis your device has.
244 the ABS_X axis::
245
246 button_dev.absmin[ABS_X] = 0;
247 button_dev.absmax[ABS_X] = 255;
248 button_dev.absfuzz[ABS_X] = 4;
249 button_dev.absflat[ABS_X] = 8;
250
251 Or, you can just say::
252
253 input_set_abs_params(button_dev, ABS_X
254
255 This setting would be appropriate for a joysti
256 0, maximum of 255 (which the joystick *must* b
257 it sometimes reports more, but it must be able
258 max values), with noise in the data up to +- 4
259 position of size 8.
260
261 If you don't need absfuzz and absflat, you can
262 that the thing is precise and always returns t
263 (if it has any).
264
265 BITS_TO_LONGS(), BIT_WORD(), BIT_MASK()
266 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
267
268 These three macros from bitops.h help some bit
269
270 BITS_TO_LONGS(x) - returns the length
271 x bits
272 BIT_WORD(x) - returns the index i
273 BIT_MASK(x) - returns the index i
274
275 The id* and name fields
276 ~~~~~~~~~~~~~~~~~~~~~~~
277
278 The dev->name should be set before registering
279 device driver. It's a string like 'Generic but
280 user friendly name of the device.
281
282 The id* fields contain the bus ID (PCI, USB, .
283 of the device. The bus IDs are defined in inpu
284 are defined in pci_ids.h, usb_ids.h and simila
285 should be set by the input device driver befor
286
287 The idtype field can be used for specific info
288 driver.
289
290 The id and name fields can be passed to userla
291
292 The keycode, keycodemax, keycodesize fields
293 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
294
295 These three fields should be used by input dev
296 The keycode is an array used to map from scanc
297 The keycode max should contain the size of the
298 size of each entry in it (in bytes).
299
300 Userspace can query and alter current scancode
301 EVIOCGKEYCODE and EVIOCSKEYCODE ioctls on corr
302 When a device has all 3 aforementioned fields
303 rely on kernel's default implementation of set
304 mappings.
305
306 dev->getkeycode() and dev->setkeycode()
307 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
308
309 getkeycode() and setkeycode() callbacks allow
310 keycode/keycodesize/keycodemax mapping mechani
311 and implement sparse keycode maps.
312
313 Key autorepeat
314 ~~~~~~~~~~~~~~
315
316 ... is simple. It is handled by the input.c mo
317 not used, because it's not present in many dev
318 present, it is broken sometimes (at keyboards:
319 autorepeat for your device, just set EV_REP in
320 handled by the input system.
321
322 Other event types, handling output events
323 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
324
325 The other event types up to now are:
326
327 - EV_LED - used for the keyboard LEDs.
328 - EV_SND - used for keyboard beeps.
329
330 They are very similar to for example key event
331 direction - from the system to the input devic
332 driver can handle these events, it has to set
333 *and* also the callback routine::
334
335 button_dev->event = button_event;
336
337 int button_event(struct input_dev *dev, un
338 unsigned int code, int va
339 {
340 if (type == EV_SND && code == SND_
341 outb(value, BUTTON_BELL);
342 return 0;
343 }
344 return -1;
345 }
346
347 This callback routine can be called from an in
348 isn't a rule), and thus must not sleep, and mu
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