view Documentation/input/input-programming.txt @ 452:c7ed6fe5dca0

kexec: dont initialise regions in reserve_memory()

There is no need to initialise efi_memmap_res and boot_param_res in
reserve_memory() for the initial xen domain as it is done in
machine_kexec_setup_resources() using values from the kexec hypercall.

Signed-off-by: Simon Horman <horms@verge.net.au>
author Keir Fraser <keir.fraser@citrix.com>
date Thu Feb 28 10:55:18 2008 +0000 (2008-02-28)
parents 831230e53067
line source
1 $Id: input-programming.txt,v 1.4 2001/05/04 09:47:14 vojtech Exp $
3 Programming input drivers
4 ~~~~~~~~~~~~~~~~~~~~~~~~~
6 1. Creating an input device driver
7 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
9 1.0 The simplest example
10 ~~~~~~~~~~~~~~~~~~~~~~~~
12 Here comes a very simple example of an input device driver. The device has
13 just one button and the button is accessible at i/o port BUTTON_PORT. When
14 pressed or released a BUTTON_IRQ happens. The driver could look like:
16 #include <linux/input.h>
17 #include <linux/module.h>
18 #include <linux/init.h>
20 #include <asm/irq.h>
21 #include <asm/io.h>
23 static void button_interrupt(int irq, void *dummy, struct pt_regs *fp)
24 {
25 input_report_key(&button_dev, BTN_1, inb(BUTTON_PORT) & 1);
26 input_sync(&button_dev);
27 }
29 static int __init button_init(void)
30 {
31 if (request_irq(BUTTON_IRQ, button_interrupt, 0, "button", NULL)) {
32 printk(KERN_ERR "button.c: Can't allocate irq %d\n", button_irq);
33 return -EBUSY;
34 }
36 button_dev.evbit[0] = BIT(EV_KEY);
37 button_dev.keybit[LONG(BTN_0)] = BIT(BTN_0);
39 input_register_device(&button_dev);
40 }
42 static void __exit button_exit(void)
43 {
44 input_unregister_device(&button_dev);
45 free_irq(BUTTON_IRQ, button_interrupt);
46 }
48 module_init(button_init);
49 module_exit(button_exit);
51 1.1 What the example does
52 ~~~~~~~~~~~~~~~~~~~~~~~~~
54 First it has to include the <linux/input.h> file, which interfaces to the
55 input subsystem. This provides all the definitions needed.
57 In the _init function, which is called either upon module load or when
58 booting the kernel, it grabs the required resources (it should also check
59 for the presence of the device).
61 Then it sets the input bitfields. This way the device driver tells the other
62 parts of the input systems what it is - what events can be generated or
63 accepted by this input device. Our example device can only generate EV_KEY type
64 events, and from those only BTN_0 event code. Thus we only set these two
65 bits. We could have used
67 set_bit(EV_KEY, button_dev.evbit);
68 set_bit(BTN_0, button_dev.keybit);
70 as well, but with more than single bits the first approach tends to be
71 shorter.
73 Then the example driver registers the input device structure by calling
75 input_register_device(&button_dev);
77 This adds the button_dev structure to linked lists of the input driver and
78 calls device handler modules _connect functions to tell them a new input
79 device has appeared. Because the _connect functions may call kmalloc(,
80 GFP_KERNEL), which can sleep, input_register_device() must not be called
81 from an interrupt or with a spinlock held.
83 While in use, the only used function of the driver is
85 button_interrupt()
87 which upon every interrupt from the button checks its state and reports it
88 via the
90 input_report_key()
92 call to the input system. There is no need to check whether the interrupt
93 routine isn't reporting two same value events (press, press for example) to
94 the input system, because the input_report_* functions check that
95 themselves.
97 Then there is the
99 input_sync()
101 call to tell those who receive the events that we've sent a complete report.
102 This doesn't seem important in the one button case, but is quite important
103 for for example mouse movement, where you don't want the X and Y values
104 to be interpreted separately, because that'd result in a different movement.
106 1.2 dev->open() and dev->close()
107 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
109 In case the driver has to repeatedly poll the device, because it doesn't
110 have an interrupt coming from it and the polling is too expensive to be done
111 all the time, or if the device uses a valuable resource (eg. interrupt), it
112 can use the open and close callback to know when it can stop polling or
113 release the interrupt and when it must resume polling or grab the interrupt
114 again. To do that, we would add this to our example driver:
116 int button_used = 0;
118 static int button_open(struct input_dev *dev)
119 {
120 if (button_used++)
121 return 0;
123 if (request_irq(BUTTON_IRQ, button_interrupt, 0, "button", NULL)) {
124 printk(KERN_ERR "button.c: Can't allocate irq %d\n", button_irq);
125 button_used--;
126 return -EBUSY;
127 }
129 return 0;
130 }
132 static void button_close(struct input_dev *dev)
133 {
134 if (!--button_used)
135 free_irq(IRQ_AMIGA_VERTB, button_interrupt);
136 }
138 static int __init button_init(void)
139 {
140 ...
141 button_dev.open = button_open;
142 button_dev.close = button_close;
143 ...
144 }
146 Note the button_used variable - we have to track how many times the open
147 function was called to know when exactly our device stops being used.
149 The open() callback should return a 0 in case of success or any nonzero value
150 in case of failure. The close() callback (which is void) must always succeed.
152 1.3 Basic event types
153 ~~~~~~~~~~~~~~~~~~~~~
155 The most simple event type is EV_KEY, which is used for keys and buttons.
156 It's reported to the input system via:
158 input_report_key(struct input_dev *dev, int code, int value)
160 See linux/input.h for the allowable values of code (from 0 to KEY_MAX).
161 Value is interpreted as a truth value, ie any nonzero value means key
162 pressed, zero value means key released. The input code generates events only
163 in case the value is different from before.
165 In addition to EV_KEY, there are two more basic event types: EV_REL and
166 EV_ABS. They are used for relative and absolute values supplied by the
167 device. A relative value may be for example a mouse movement in the X axis.
168 The mouse reports it as a relative difference from the last position,
169 because it doesn't have any absolute coordinate system to work in. Absolute
170 events are namely for joysticks and digitizers - devices that do work in an
171 absolute coordinate systems.
173 Having the device report EV_REL buttons is as simple as with EV_KEY, simply
174 set the corresponding bits and call the
176 input_report_rel(struct input_dev *dev, int code, int value)
178 function. Events are generated only for nonzero value.
180 However EV_ABS requires a little special care. Before calling
181 input_register_device, you have to fill additional fields in the input_dev
182 struct for each absolute axis your device has. If our button device had also
183 the ABS_X axis:
185 button_dev.absmin[ABS_X] = 0;
186 button_dev.absmax[ABS_X] = 255;
187 button_dev.absfuzz[ABS_X] = 4;
188 button_dev.absflat[ABS_X] = 8;
190 This setting would be appropriate for a joystick X axis, with the minimum of
191 0, maximum of 255 (which the joystick *must* be able to reach, no problem if
192 it sometimes reports more, but it must be able to always reach the min and
193 max values), with noise in the data up to +- 4, and with a center flat
194 position of size 8.
196 If you don't need absfuzz and absflat, you can set them to zero, which mean
197 that the thing is precise and always returns to exactly the center position
198 (if it has any).
200 1.4 The void *private field
201 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
203 This field in the input structure can be used to point to any private data
204 structures in the input device driver, in case the driver handles more than
205 one device. You'll need it in the open and close callbacks.
207 1.5 NBITS(), LONG(), BIT()
208 ~~~~~~~~~~~~~~~~~~~~~~~~~~
210 These three macros from input.h help some bitfield computations:
212 NBITS(x) - returns the length of a bitfield array in longs for x bits
213 LONG(x) - returns the index in the array in longs for bit x
214 BIT(x) - returns the index in a long for bit x
216 1.6 The number, id* and name fields
217 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
219 The dev->number is assigned by the input system to the input device when it
220 is registered. It has no use except for identifying the device to the user
221 in system messages.
223 The dev->name should be set before registering the input device by the input
224 device driver. It's a string like 'Generic button device' containing a
225 user friendly name of the device.
227 The id* fields contain the bus ID (PCI, USB, ...), vendor ID and device ID
228 of the device. The bus IDs are defined in input.h. The vendor and device ids
229 are defined in pci_ids.h, usb_ids.h and similar include files. These fields
230 should be set by the input device driver before registering it.
232 The idtype field can be used for specific information for the input device
233 driver.
235 The id and name fields can be passed to userland via the evdev interface.
237 1.7 The keycode, keycodemax, keycodesize fields
238 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
240 These two fields will be used for any input devices that report their data
241 as scancodes. If not all scancodes can be known by autodetection, they may
242 need to be set by userland utilities. The keycode array then is an array
243 used to map from scancodes to input system keycodes. The keycode max will
244 contain the size of the array and keycodesize the size of each entry in it
245 (in bytes).
247 1.8 Key autorepeat
248 ~~~~~~~~~~~~~~~~~~
250 ... is simple. It is handled by the input.c module. Hardware autorepeat is
251 not used, because it's not present in many devices and even where it is
252 present, it is broken sometimes (at keyboards: Toshiba notebooks). To enable
253 autorepeat for your device, just set EV_REP in dev->evbit. All will be
254 handled by the input system.
256 1.9 Other event types, handling output events
257 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
259 The other event types up to now are:
261 EV_LED - used for the keyboard LEDs.
262 EV_SND - used for keyboard beeps.
264 They are very similar to for example key events, but they go in the other
265 direction - from the system to the input device driver. If your input device
266 driver can handle these events, it has to set the respective bits in evbit,
267 *and* also the callback routine:
269 button_dev.event = button_event;
271 int button_event(struct input_dev *dev, unsigned int type, unsigned int code, int value);
272 {
273 if (type == EV_SND && code == SND_BELL) {
274 outb(value, BUTTON_BELL);
275 return 0;
276 }
277 return -1;
278 }
280 This callback routine can be called from an interrupt or a BH (although that
281 isn't a rule), and thus must not sleep, and must not take too long to finish.