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Linus Torvalds1da177e2005-04-16 15:20:36 -07001This is a small guide for those who want to write kernel drivers for I2C
2or SMBus devices.
3
4To set up a driver, you need to do several things. Some are optional, and
5some things can be done slightly or completely different. Use this as a
6guide, not as a rule book!
7
8
9General remarks
10===============
11
12Try to keep the kernel namespace as clean as possible. The best way to
13do this is to use a unique prefix for all global symbols. This is
14especially important for exported symbols, but it is a good idea to do
15it for non-exported symbols too. We will use the prefix `foo_' in this
16tutorial, and `FOO_' for preprocessor variables.
17
18
19The driver structure
20====================
21
22Usually, you will implement a single driver structure, and instantiate
23all clients from it. Remember, a driver structure contains general access
24routines, a client structure specific information like the actual I2C
25address.
26
27static struct i2c_driver foo_driver = {
Jean Delvared45d2042005-11-26 20:55:35 +010028 .driver = {
Jean Delvared45d2042005-11-26 20:55:35 +010029 .name = "foo",
30 },
Linus Torvalds1da177e2005-04-16 15:20:36 -070031 .attach_adapter = &foo_attach_adapter,
32 .detach_client = &foo_detach_client,
33 .command = &foo_command /* may be NULL */
34}
35
Jean Delvare7865e242005-10-08 00:00:31 +020036The name field must match the driver name, including the case. It must not
37contain spaces, and may be up to 31 characters long.
Linus Torvalds1da177e2005-04-16 15:20:36 -070038
Linus Torvalds1da177e2005-04-16 15:20:36 -070039All other fields are for call-back functions which will be explained
40below.
41
Linus Torvalds1da177e2005-04-16 15:20:36 -070042
43Extra client data
44=================
45
46The client structure has a special `data' field that can point to any
47structure at all. You can use this to keep client-specific data. You
48do not always need this, but especially for `sensors' drivers, it can
49be very useful.
50
51An example structure is below.
52
53 struct foo_data {
Jean Delvare2445eb62005-10-17 23:16:25 +020054 struct i2c_client client;
Linus Torvalds1da177e2005-04-16 15:20:36 -070055 struct semaphore lock; /* For ISA access in `sensors' drivers. */
56 int sysctl_id; /* To keep the /proc directory entry for
57 `sensors' drivers. */
58 enum chips type; /* To keep the chips type for `sensors' drivers. */
59
60 /* Because the i2c bus is slow, it is often useful to cache the read
61 information of a chip for some time (for example, 1 or 2 seconds).
62 It depends of course on the device whether this is really worthwhile
63 or even sensible. */
64 struct semaphore update_lock; /* When we are reading lots of information,
65 another process should not update the
66 below information */
67 char valid; /* != 0 if the following fields are valid. */
68 unsigned long last_updated; /* In jiffies */
69 /* Add the read information here too */
70 };
71
72
73Accessing the client
74====================
75
76Let's say we have a valid client structure. At some time, we will need
77to gather information from the client, or write new information to the
78client. How we will export this information to user-space is less
79important at this moment (perhaps we do not need to do this at all for
80some obscure clients). But we need generic reading and writing routines.
81
82I have found it useful to define foo_read and foo_write function for this.
83For some cases, it will be easier to call the i2c functions directly,
84but many chips have some kind of register-value idea that can easily
85be encapsulated. Also, some chips have both ISA and I2C interfaces, and
86it useful to abstract from this (only for `sensors' drivers).
87
88The below functions are simple examples, and should not be copied
89literally.
90
91 int foo_read_value(struct i2c_client *client, u8 reg)
92 {
93 if (reg < 0x10) /* byte-sized register */
94 return i2c_smbus_read_byte_data(client,reg);
95 else /* word-sized register */
96 return i2c_smbus_read_word_data(client,reg);
97 }
98
99 int foo_write_value(struct i2c_client *client, u8 reg, u16 value)
100 {
101 if (reg == 0x10) /* Impossible to write - driver error! */ {
102 return -1;
103 else if (reg < 0x10) /* byte-sized register */
104 return i2c_smbus_write_byte_data(client,reg,value);
105 else /* word-sized register */
106 return i2c_smbus_write_word_data(client,reg,value);
107 }
108
109For sensors code, you may have to cope with ISA registers too. Something
110like the below often works. Note the locking!
111
112 int foo_read_value(struct i2c_client *client, u8 reg)
113 {
114 int res;
115 if (i2c_is_isa_client(client)) {
116 down(&(((struct foo_data *) (client->data)) -> lock));
117 outb_p(reg,client->addr + FOO_ADDR_REG_OFFSET);
118 res = inb_p(client->addr + FOO_DATA_REG_OFFSET);
119 up(&(((struct foo_data *) (client->data)) -> lock));
120 return res;
121 } else
122 return i2c_smbus_read_byte_data(client,reg);
123 }
124
125Writing is done the same way.
126
127
128Probing and attaching
129=====================
130
131Most i2c devices can be present on several i2c addresses; for some this
132is determined in hardware (by soldering some chip pins to Vcc or Ground),
133for others this can be changed in software (by writing to specific client
134registers). Some devices are usually on a specific address, but not always;
135and some are even more tricky. So you will probably need to scan several
136i2c addresses for your clients, and do some sort of detection to see
137whether it is actually a device supported by your driver.
138
139To give the user a maximum of possibilities, some default module parameters
140are defined to help determine what addresses are scanned. Several macros
141are defined in i2c.h to help you support them, as well as a generic
142detection algorithm.
143
144You do not have to use this parameter interface; but don't try to use
Jean Delvare2ed2dc32005-07-31 21:42:02 +0200145function i2c_probe() if you don't.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700146
147NOTE: If you want to write a `sensors' driver, the interface is slightly
148 different! See below.
149
150
151
Jean Delvaref4b50262005-07-31 21:49:03 +0200152Probing classes
153---------------
Linus Torvalds1da177e2005-04-16 15:20:36 -0700154
155All parameters are given as lists of unsigned 16-bit integers. Lists are
156terminated by I2C_CLIENT_END.
157The following lists are used internally:
158
159 normal_i2c: filled in by the module writer.
160 A list of I2C addresses which should normally be examined.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700161 probe: insmod parameter.
162 A list of pairs. The first value is a bus number (-1 for any I2C bus),
163 the second is the address. These addresses are also probed, as if they
164 were in the 'normal' list.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700165 ignore: insmod parameter.
166 A list of pairs. The first value is a bus number (-1 for any I2C bus),
167 the second is the I2C address. These addresses are never probed.
Jean Delvaref4b50262005-07-31 21:49:03 +0200168 This parameter overrules the 'normal_i2c' list only.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700169 force: insmod parameter.
170 A list of pairs. The first value is a bus number (-1 for any I2C bus),
171 the second is the I2C address. A device is blindly assumed to be on
172 the given address, no probing is done.
173
Jean Delvaref4b50262005-07-31 21:49:03 +0200174Additionally, kind-specific force lists may optionally be defined if
175the driver supports several chip kinds. They are grouped in a
176NULL-terminated list of pointers named forces, those first element if the
177generic force list mentioned above. Each additional list correspond to an
178insmod parameter of the form force_<kind>.
179
Jean Delvareb3d54962005-04-02 20:31:02 +0200180Fortunately, as a module writer, you just have to define the `normal_i2c'
181parameter. The complete declaration could look like this:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700182
Jean Delvareb3d54962005-04-02 20:31:02 +0200183 /* Scan 0x37, and 0x48 to 0x4f */
184 static unsigned short normal_i2c[] = { 0x37, 0x48, 0x49, 0x4a, 0x4b, 0x4c,
185 0x4d, 0x4e, 0x4f, I2C_CLIENT_END };
Linus Torvalds1da177e2005-04-16 15:20:36 -0700186
187 /* Magic definition of all other variables and things */
188 I2C_CLIENT_INSMOD;
Jean Delvaref4b50262005-07-31 21:49:03 +0200189 /* Or, if your driver supports, say, 2 kind of devices: */
190 I2C_CLIENT_INSMOD_2(foo, bar);
191
192If you use the multi-kind form, an enum will be defined for you:
193 enum chips { any_chip, foo, bar, ... }
194You can then (and certainly should) use it in the driver code.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700195
Jean Delvareb3d54962005-04-02 20:31:02 +0200196Note that you *have* to call the defined variable `normal_i2c',
197without any prefix!
Linus Torvalds1da177e2005-04-16 15:20:36 -0700198
199
Linus Torvalds1da177e2005-04-16 15:20:36 -0700200Attaching to an adapter
201-----------------------
202
203Whenever a new adapter is inserted, or for all adapters if the driver is
204being registered, the callback attach_adapter() is called. Now is the
205time to determine what devices are present on the adapter, and to register
206a client for each of them.
207
208The attach_adapter callback is really easy: we just call the generic
209detection function. This function will scan the bus for us, using the
210information as defined in the lists explained above. If a device is
211detected at a specific address, another callback is called.
212
213 int foo_attach_adapter(struct i2c_adapter *adapter)
214 {
215 return i2c_probe(adapter,&addr_data,&foo_detect_client);
216 }
217
Linus Torvalds1da177e2005-04-16 15:20:36 -0700218Remember, structure `addr_data' is defined by the macros explained above,
219so you do not have to define it yourself.
220
Jean Delvare2ed2dc32005-07-31 21:42:02 +0200221The i2c_probe function will call the foo_detect_client
Linus Torvalds1da177e2005-04-16 15:20:36 -0700222function only for those i2c addresses that actually have a device on
223them (unless a `force' parameter was used). In addition, addresses that
224are already in use (by some other registered client) are skipped.
225
226
227The detect client function
228--------------------------
229
Jean Delvare2ed2dc32005-07-31 21:42:02 +0200230The detect client function is called by i2c_probe. The `kind' parameter
231contains -1 for a probed detection, 0 for a forced detection, or a positive
232number for a forced detection with a chip type forced.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700233
234Below, some things are only needed if this is a `sensors' driver. Those
235parts are between /* SENSORS ONLY START */ and /* SENSORS ONLY END */
236markers.
237
Jean Delvarea89ba0b2005-08-09 20:17:55 +0200238Returning an error different from -ENODEV in a detect function will cause
239the detection to stop: other addresses and adapters won't be scanned.
240This should only be done on fatal or internal errors, such as a memory
241shortage or i2c_attach_client failing.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700242
243For now, you can ignore the `flags' parameter. It is there for future use.
244
245 int foo_detect_client(struct i2c_adapter *adapter, int address,
246 unsigned short flags, int kind)
247 {
248 int err = 0;
249 int i;
250 struct i2c_client *new_client;
251 struct foo_data *data;
252 const char *client_name = ""; /* For non-`sensors' drivers, put the real
253 name here! */
254
255 /* Let's see whether this adapter can support what we need.
256 Please substitute the things you need here!
257 For `sensors' drivers, add `! is_isa &&' to the if statement */
258 if (!i2c_check_functionality(adapter,I2C_FUNC_SMBUS_WORD_DATA |
259 I2C_FUNC_SMBUS_WRITE_BYTE))
260 goto ERROR0;
261
262 /* SENSORS ONLY START */
263 const char *type_name = "";
264 int is_isa = i2c_is_isa_adapter(adapter);
265
Jean Delvare02ff9822005-07-20 00:05:33 +0200266 /* Do this only if the chip can additionally be found on the ISA bus
267 (hybrid chip). */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700268
Jean Delvare02ff9822005-07-20 00:05:33 +0200269 if (is_isa) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700270
271 /* Discard immediately if this ISA range is already used */
Jeff Garzikd61780c2005-10-30 15:01:51 -0800272 /* FIXME: never use check_region(), only request_region() */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700273 if (check_region(address,FOO_EXTENT))
274 goto ERROR0;
275
276 /* Probe whether there is anything on this address.
277 Some example code is below, but you will have to adapt this
278 for your own driver */
279
280 if (kind < 0) /* Only if no force parameter was used */ {
281 /* We may need long timeouts at least for some chips. */
282 #define REALLY_SLOW_IO
283 i = inb_p(address + 1);
284 if (inb_p(address + 2) != i)
285 goto ERROR0;
286 if (inb_p(address + 3) != i)
287 goto ERROR0;
288 if (inb_p(address + 7) != i)
289 goto ERROR0;
290 #undef REALLY_SLOW_IO
291
292 /* Let's just hope nothing breaks here */
293 i = inb_p(address + 5) & 0x7f;
294 outb_p(~i & 0x7f,address+5);
295 if ((inb_p(address + 5) & 0x7f) != (~i & 0x7f)) {
296 outb_p(i,address+5);
297 return 0;
298 }
299 }
300 }
301
302 /* SENSORS ONLY END */
303
304 /* OK. For now, we presume we have a valid client. We now create the
305 client structure, even though we cannot fill it completely yet.
306 But it allows us to access several i2c functions safely */
307
Jean Delvare2445eb62005-10-17 23:16:25 +0200308 if (!(data = kzalloc(sizeof(struct foo_data), GFP_KERNEL))) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700309 err = -ENOMEM;
310 goto ERROR0;
311 }
312
Jean Delvare2445eb62005-10-17 23:16:25 +0200313 new_client = &data->client;
314 i2c_set_clientdata(new_client, data);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700315
316 new_client->addr = address;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700317 new_client->adapter = adapter;
318 new_client->driver = &foo_driver;
319 new_client->flags = 0;
320
321 /* Now, we do the remaining detection. If no `force' parameter is used. */
322
323 /* First, the generic detection (if any), that is skipped if any force
324 parameter was used. */
325 if (kind < 0) {
326 /* The below is of course bogus */
327 if (foo_read(new_client,FOO_REG_GENERIC) != FOO_GENERIC_VALUE)
328 goto ERROR1;
329 }
330
331 /* SENSORS ONLY START */
332
333 /* Next, specific detection. This is especially important for `sensors'
334 devices. */
335
336 /* Determine the chip type. Not needed if a `force_CHIPTYPE' parameter
337 was used. */
338 if (kind <= 0) {
339 i = foo_read(new_client,FOO_REG_CHIPTYPE);
340 if (i == FOO_TYPE_1)
341 kind = chip1; /* As defined in the enum */
342 else if (i == FOO_TYPE_2)
343 kind = chip2;
344 else {
345 printk("foo: Ignoring 'force' parameter for unknown chip at "
346 "adapter %d, address 0x%02x\n",i2c_adapter_id(adapter),address);
347 goto ERROR1;
348 }
349 }
350
351 /* Now set the type and chip names */
352 if (kind == chip1) {
353 type_name = "chip1"; /* For /proc entry */
354 client_name = "CHIP 1";
355 } else if (kind == chip2) {
356 type_name = "chip2"; /* For /proc entry */
357 client_name = "CHIP 2";
358 }
359
360 /* Reserve the ISA region */
361 if (is_isa)
362 request_region(address,FOO_EXTENT,type_name);
363
364 /* SENSORS ONLY END */
365
366 /* Fill in the remaining client fields. */
367 strcpy(new_client->name,client_name);
368
369 /* SENSORS ONLY BEGIN */
370 data->type = kind;
371 /* SENSORS ONLY END */
372
373 data->valid = 0; /* Only if you use this field */
374 init_MUTEX(&data->update_lock); /* Only if you use this field */
375
376 /* Any other initializations in data must be done here too. */
377
378 /* Tell the i2c layer a new client has arrived */
379 if ((err = i2c_attach_client(new_client)))
380 goto ERROR3;
381
382 /* SENSORS ONLY BEGIN */
383 /* Register a new directory entry with module sensors. See below for
384 the `template' structure. */
385 if ((i = i2c_register_entry(new_client, type_name,
386 foo_dir_table_template,THIS_MODULE)) < 0) {
387 err = i;
388 goto ERROR4;
389 }
390 data->sysctl_id = i;
391
392 /* SENSORS ONLY END */
393
394 /* This function can write default values to the client registers, if
395 needed. */
396 foo_init_client(new_client);
397 return 0;
398
399 /* OK, this is not exactly good programming practice, usually. But it is
400 very code-efficient in this case. */
401
402 ERROR4:
403 i2c_detach_client(new_client);
404 ERROR3:
405 ERROR2:
406 /* SENSORS ONLY START */
407 if (is_isa)
408 release_region(address,FOO_EXTENT);
409 /* SENSORS ONLY END */
410 ERROR1:
Jean Delvarea852daa2005-11-02 21:42:48 +0100411 kfree(data);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700412 ERROR0:
413 return err;
414 }
415
416
417Removing the client
418===================
419
420The detach_client call back function is called when a client should be
421removed. It may actually fail, but only when panicking. This code is
422much simpler than the attachment code, fortunately!
423
424 int foo_detach_client(struct i2c_client *client)
425 {
426 int err,i;
427
428 /* SENSORS ONLY START */
429 /* Deregister with the `i2c-proc' module. */
430 i2c_deregister_entry(((struct lm78_data *)(client->data))->sysctl_id);
431 /* SENSORS ONLY END */
432
433 /* Try to detach the client from i2c space */
Jean Delvare7bef5592005-07-27 22:14:49 +0200434 if ((err = i2c_detach_client(client)))
Linus Torvalds1da177e2005-04-16 15:20:36 -0700435 return err;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700436
Jean Delvare02ff9822005-07-20 00:05:33 +0200437 /* HYBRID SENSORS CHIP ONLY START */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700438 if i2c_is_isa_client(client)
439 release_region(client->addr,LM78_EXTENT);
Jean Delvare02ff9822005-07-20 00:05:33 +0200440 /* HYBRID SENSORS CHIP ONLY END */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700441
Jean Delvarea852daa2005-11-02 21:42:48 +0100442 kfree(i2c_get_clientdata(client));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700443 return 0;
444 }
445
446
447Initializing the module or kernel
448=================================
449
450When the kernel is booted, or when your foo driver module is inserted,
451you have to do some initializing. Fortunately, just attaching (registering)
452the driver module is usually enough.
453
454 /* Keep track of how far we got in the initialization process. If several
455 things have to initialized, and we fail halfway, only those things
456 have to be cleaned up! */
457 static int __initdata foo_initialized = 0;
458
459 static int __init foo_init(void)
460 {
461 int res;
462 printk("foo version %s (%s)\n",FOO_VERSION,FOO_DATE);
463
464 if ((res = i2c_add_driver(&foo_driver))) {
465 printk("foo: Driver registration failed, module not inserted.\n");
466 foo_cleanup();
467 return res;
468 }
469 foo_initialized ++;
470 return 0;
471 }
472
473 void foo_cleanup(void)
474 {
475 if (foo_initialized == 1) {
476 if ((res = i2c_del_driver(&foo_driver))) {
477 printk("foo: Driver registration failed, module not removed.\n");
478 return;
479 }
480 foo_initialized --;
481 }
482 }
483
484 /* Substitute your own name and email address */
485 MODULE_AUTHOR("Frodo Looijaard <frodol@dds.nl>"
486 MODULE_DESCRIPTION("Driver for Barf Inc. Foo I2C devices");
487
488 module_init(foo_init);
489 module_exit(foo_cleanup);
490
491Note that some functions are marked by `__init', and some data structures
492by `__init_data'. Hose functions and structures can be removed after
493kernel booting (or module loading) is completed.
494
Jean Delvarefb687d72005-12-18 16:51:55 +0100495
Linus Torvalds1da177e2005-04-16 15:20:36 -0700496Command function
497================
498
499A generic ioctl-like function call back is supported. You will seldom
Jean Delvarefb687d72005-12-18 16:51:55 +0100500need this, and its use is deprecated anyway, so newer design should not
501use it. Set it to NULL.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700502
503
504Sending and receiving
505=====================
506
507If you want to communicate with your device, there are several functions
508to do this. You can find all of them in i2c.h.
509
510If you can choose between plain i2c communication and SMBus level
511communication, please use the last. All adapters understand SMBus level
512commands, but only some of them understand plain i2c!
513
514
515Plain i2c communication
516-----------------------
517
518 extern int i2c_master_send(struct i2c_client *,const char* ,int);
519 extern int i2c_master_recv(struct i2c_client *,char* ,int);
520
521These routines read and write some bytes from/to a client. The client
522contains the i2c address, so you do not have to include it. The second
523parameter contains the bytes the read/write, the third the length of the
524buffer. Returned is the actual number of bytes read/written.
525
526 extern int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msg,
527 int num);
528
529This sends a series of messages. Each message can be a read or write,
530and they can be mixed in any way. The transactions are combined: no
531stop bit is sent between transaction. The i2c_msg structure contains
532for each message the client address, the number of bytes of the message
533and the message data itself.
534
535You can read the file `i2c-protocol' for more information about the
536actual i2c protocol.
537
538
539SMBus communication
540-------------------
541
542 extern s32 i2c_smbus_xfer (struct i2c_adapter * adapter, u16 addr,
543 unsigned short flags,
544 char read_write, u8 command, int size,
545 union i2c_smbus_data * data);
546
547 This is the generic SMBus function. All functions below are implemented
548 in terms of it. Never use this function directly!
549
550
551 extern s32 i2c_smbus_write_quick(struct i2c_client * client, u8 value);
552 extern s32 i2c_smbus_read_byte(struct i2c_client * client);
553 extern s32 i2c_smbus_write_byte(struct i2c_client * client, u8 value);
554 extern s32 i2c_smbus_read_byte_data(struct i2c_client * client, u8 command);
555 extern s32 i2c_smbus_write_byte_data(struct i2c_client * client,
556 u8 command, u8 value);
557 extern s32 i2c_smbus_read_word_data(struct i2c_client * client, u8 command);
558 extern s32 i2c_smbus_write_word_data(struct i2c_client * client,
559 u8 command, u16 value);
560 extern s32 i2c_smbus_write_block_data(struct i2c_client * client,
561 u8 command, u8 length,
562 u8 *values);
Jean Delvare7865e242005-10-08 00:00:31 +0200563 extern s32 i2c_smbus_read_i2c_block_data(struct i2c_client * client,
564 u8 command, u8 *values);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700565
566These ones were removed in Linux 2.6.10 because they had no users, but could
567be added back later if needed:
568
Linus Torvalds1da177e2005-04-16 15:20:36 -0700569 extern s32 i2c_smbus_read_block_data(struct i2c_client * client,
570 u8 command, u8 *values);
571 extern s32 i2c_smbus_write_i2c_block_data(struct i2c_client * client,
572 u8 command, u8 length,
573 u8 *values);
574 extern s32 i2c_smbus_process_call(struct i2c_client * client,
575 u8 command, u16 value);
576 extern s32 i2c_smbus_block_process_call(struct i2c_client *client,
577 u8 command, u8 length,
578 u8 *values)
579
580All these transactions return -1 on failure. The 'write' transactions
581return 0 on success; the 'read' transactions return the read value, except
582for read_block, which returns the number of values read. The block buffers
583need not be longer than 32 bytes.
584
585You can read the file `smbus-protocol' for more information about the
586actual SMBus protocol.
587
588
589General purpose routines
590========================
591
592Below all general purpose routines are listed, that were not mentioned
593before.
594
595 /* This call returns a unique low identifier for each registered adapter,
596 * or -1 if the adapter was not registered.
597 */
598 extern int i2c_adapter_id(struct i2c_adapter *adap);
599
600
601The sensors sysctl/proc interface
602=================================
603
604This section only applies if you write `sensors' drivers.
605
606Each sensors driver creates a directory in /proc/sys/dev/sensors for each
607registered client. The directory is called something like foo-i2c-4-65.
608The sensors module helps you to do this as easily as possible.
609
610The template
611------------
612
613You will need to define a ctl_table template. This template will automatically
614be copied to a newly allocated structure and filled in where necessary when
615you call sensors_register_entry.
616
617First, I will give an example definition.
618 static ctl_table foo_dir_table_template[] = {
619 { FOO_SYSCTL_FUNC1, "func1", NULL, 0, 0644, NULL, &i2c_proc_real,
620 &i2c_sysctl_real,NULL,&foo_func },
621 { FOO_SYSCTL_FUNC2, "func2", NULL, 0, 0644, NULL, &i2c_proc_real,
622 &i2c_sysctl_real,NULL,&foo_func },
623 { FOO_SYSCTL_DATA, "data", NULL, 0, 0644, NULL, &i2c_proc_real,
624 &i2c_sysctl_real,NULL,&foo_data },
625 { 0 }
626 };
627
628In the above example, three entries are defined. They can either be
629accessed through the /proc interface, in the /proc/sys/dev/sensors/*
630directories, as files named func1, func2 and data, or alternatively
631through the sysctl interface, in the appropriate table, with identifiers
632FOO_SYSCTL_FUNC1, FOO_SYSCTL_FUNC2 and FOO_SYSCTL_DATA.
633
634The third, sixth and ninth parameters should always be NULL, and the
635fourth should always be 0. The fifth is the mode of the /proc file;
6360644 is safe, as the file will be owned by root:root.
637
638The seventh and eighth parameters should be &i2c_proc_real and
639&i2c_sysctl_real if you want to export lists of reals (scaled
640integers). You can also use your own function for them, as usual.
641Finally, the last parameter is the call-back to gather the data
642(see below) if you use the *_proc_real functions.
643
644
645Gathering the data
646------------------
647
648The call back functions (foo_func and foo_data in the above example)
649can be called in several ways; the operation parameter determines
650what should be done:
651
652 * If operation == SENSORS_PROC_REAL_INFO, you must return the
653 magnitude (scaling) in nrels_mag;
654 * If operation == SENSORS_PROC_REAL_READ, you must read information
655 from the chip and return it in results. The number of integers
656 to display should be put in nrels_mag;
657 * If operation == SENSORS_PROC_REAL_WRITE, you must write the
658 supplied information to the chip. nrels_mag will contain the number
659 of integers, results the integers themselves.
660
661The *_proc_real functions will display the elements as reals for the
662/proc interface. If you set the magnitude to 2, and supply 345 for
663SENSORS_PROC_REAL_READ, it would display 3.45; and if the user would
664write 45.6 to the /proc file, it would be returned as 4560 for
665SENSORS_PROC_REAL_WRITE. A magnitude may even be negative!
666
667An example function:
668
669 /* FOO_FROM_REG and FOO_TO_REG translate between scaled values and
670 register values. Note the use of the read cache. */
671 void foo_in(struct i2c_client *client, int operation, int ctl_name,
672 int *nrels_mag, long *results)
673 {
674 struct foo_data *data = client->data;
675 int nr = ctl_name - FOO_SYSCTL_FUNC1; /* reduce to 0 upwards */
676
677 if (operation == SENSORS_PROC_REAL_INFO)
678 *nrels_mag = 2;
679 else if (operation == SENSORS_PROC_REAL_READ) {
680 /* Update the readings cache (if necessary) */
681 foo_update_client(client);
682 /* Get the readings from the cache */
683 results[0] = FOO_FROM_REG(data->foo_func_base[nr]);
684 results[1] = FOO_FROM_REG(data->foo_func_more[nr]);
685 results[2] = FOO_FROM_REG(data->foo_func_readonly[nr]);
686 *nrels_mag = 2;
687 } else if (operation == SENSORS_PROC_REAL_WRITE) {
688 if (*nrels_mag >= 1) {
689 /* Update the cache */
690 data->foo_base[nr] = FOO_TO_REG(results[0]);
691 /* Update the chip */
692 foo_write_value(client,FOO_REG_FUNC_BASE(nr),data->foo_base[nr]);
693 }
694 if (*nrels_mag >= 2) {
695 /* Update the cache */
696 data->foo_more[nr] = FOO_TO_REG(results[1]);
697 /* Update the chip */
698 foo_write_value(client,FOO_REG_FUNC_MORE(nr),data->foo_more[nr]);
699 }
700 }
701 }