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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 18:20:36 -0400
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 18:20:36 -0400
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/i2c/writing-clients
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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1This 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 = {
28 .owner = THIS_MODULE,
29 .name = "Foo version 2.3 driver",
30 .id = I2C_DRIVERID_FOO, /* from i2c-id.h, optional */
31 .flags = I2C_DF_NOTIFY,
32 .attach_adapter = &foo_attach_adapter,
33 .detach_client = &foo_detach_client,
34 .command = &foo_command /* may be NULL */
35}
36
37The name can be chosen freely, and may be upto 40 characters long. Please
38use something descriptive here.
39
40If used, the id should be a unique ID. The range 0xf000 to 0xffff is
41reserved for local use, and you can use one of those until you start
42distributing the driver, at which time you should contact the i2c authors
43to get your own ID(s). Note that most of the time you don't need an ID
44at all so you can just omit it.
45
46Don't worry about the flags field; just put I2C_DF_NOTIFY into it. This
47means that your driver will be notified when new adapters are found.
48This is almost always what you want.
49
50All other fields are for call-back functions which will be explained
51below.
52
53There use to be two additional fields in this structure, inc_use et dec_use,
54for module usage count, but these fields were obsoleted and removed.
55
56
57Extra client data
58=================
59
60The client structure has a special `data' field that can point to any
61structure at all. You can use this to keep client-specific data. You
62do not always need this, but especially for `sensors' drivers, it can
63be very useful.
64
65An example structure is below.
66
67 struct foo_data {
68 struct semaphore lock; /* For ISA access in `sensors' drivers. */
69 int sysctl_id; /* To keep the /proc directory entry for
70 `sensors' drivers. */
71 enum chips type; /* To keep the chips type for `sensors' drivers. */
72
73 /* Because the i2c bus is slow, it is often useful to cache the read
74 information of a chip for some time (for example, 1 or 2 seconds).
75 It depends of course on the device whether this is really worthwhile
76 or even sensible. */
77 struct semaphore update_lock; /* When we are reading lots of information,
78 another process should not update the
79 below information */
80 char valid; /* != 0 if the following fields are valid. */
81 unsigned long last_updated; /* In jiffies */
82 /* Add the read information here too */
83 };
84
85
86Accessing the client
87====================
88
89Let's say we have a valid client structure. At some time, we will need
90to gather information from the client, or write new information to the
91client. How we will export this information to user-space is less
92important at this moment (perhaps we do not need to do this at all for
93some obscure clients). But we need generic reading and writing routines.
94
95I have found it useful to define foo_read and foo_write function for this.
96For some cases, it will be easier to call the i2c functions directly,
97but many chips have some kind of register-value idea that can easily
98be encapsulated. Also, some chips have both ISA and I2C interfaces, and
99it useful to abstract from this (only for `sensors' drivers).
100
101The below functions are simple examples, and should not be copied
102literally.
103
104 int foo_read_value(struct i2c_client *client, u8 reg)
105 {
106 if (reg < 0x10) /* byte-sized register */
107 return i2c_smbus_read_byte_data(client,reg);
108 else /* word-sized register */
109 return i2c_smbus_read_word_data(client,reg);
110 }
111
112 int foo_write_value(struct i2c_client *client, u8 reg, u16 value)
113 {
114 if (reg == 0x10) /* Impossible to write - driver error! */ {
115 return -1;
116 else if (reg < 0x10) /* byte-sized register */
117 return i2c_smbus_write_byte_data(client,reg,value);
118 else /* word-sized register */
119 return i2c_smbus_write_word_data(client,reg,value);
120 }
121
122For sensors code, you may have to cope with ISA registers too. Something
123like the below often works. Note the locking!
124
125 int foo_read_value(struct i2c_client *client, u8 reg)
126 {
127 int res;
128 if (i2c_is_isa_client(client)) {
129 down(&(((struct foo_data *) (client->data)) -> lock));
130 outb_p(reg,client->addr + FOO_ADDR_REG_OFFSET);
131 res = inb_p(client->addr + FOO_DATA_REG_OFFSET);
132 up(&(((struct foo_data *) (client->data)) -> lock));
133 return res;
134 } else
135 return i2c_smbus_read_byte_data(client,reg);
136 }
137
138Writing is done the same way.
139
140
141Probing and attaching
142=====================
143
144Most i2c devices can be present on several i2c addresses; for some this
145is determined in hardware (by soldering some chip pins to Vcc or Ground),
146for others this can be changed in software (by writing to specific client
147registers). Some devices are usually on a specific address, but not always;
148and some are even more tricky. So you will probably need to scan several
149i2c addresses for your clients, and do some sort of detection to see
150whether it is actually a device supported by your driver.
151
152To give the user a maximum of possibilities, some default module parameters
153are defined to help determine what addresses are scanned. Several macros
154are defined in i2c.h to help you support them, as well as a generic
155detection algorithm.
156
157You do not have to use this parameter interface; but don't try to use
158function i2c_probe() (or i2c_detect()) if you don't.
159
160NOTE: If you want to write a `sensors' driver, the interface is slightly
161 different! See below.
162
163
164
165Probing classes (i2c)
166---------------------
167
168All parameters are given as lists of unsigned 16-bit integers. Lists are
169terminated by I2C_CLIENT_END.
170The following lists are used internally:
171
172 normal_i2c: filled in by the module writer.
173 A list of I2C addresses which should normally be examined.
174 normal_i2c_range: filled in by the module writer.
175 A list of pairs of I2C addresses, each pair being an inclusive range of
176 addresses which should normally be examined.
177 probe: insmod parameter.
178 A list of pairs. The first value is a bus number (-1 for any I2C bus),
179 the second is the address. These addresses are also probed, as if they
180 were in the 'normal' list.
181 probe_range: insmod parameter.
182 A list of triples. The first value is a bus number (-1 for any I2C bus),
183 the second and third are addresses. These form an inclusive range of
184 addresses that are also probed, as if they were in the 'normal' list.
185 ignore: insmod parameter.
186 A list of pairs. The first value is a bus number (-1 for any I2C bus),
187 the second is the I2C address. These addresses are never probed.
188 This parameter overrules 'normal' and 'probe', but not the 'force' lists.
189 ignore_range: insmod parameter.
190 A list of triples. The first value is a bus number (-1 for any I2C bus),
191 the second and third are addresses. These form an inclusive range of
192 I2C addresses that are never probed.
193 This parameter overrules 'normal' and 'probe', but not the 'force' lists.
194 force: insmod parameter.
195 A list of pairs. The first value is a bus number (-1 for any I2C bus),
196 the second is the I2C address. A device is blindly assumed to be on
197 the given address, no probing is done.
198
199Fortunately, as a module writer, you just have to define the `normal'
200and/or `normal_range' parameters. The complete declaration could look
201like this:
202
203 /* Scan 0x20 to 0x2f, 0x37, and 0x40 to 0x4f */
204 static unsigned short normal_i2c[] = { 0x37,I2C_CLIENT_END };
205 static unsigned short normal_i2c_range[] = { 0x20, 0x2f, 0x40, 0x4f,
206 I2C_CLIENT_END };
207
208 /* Magic definition of all other variables and things */
209 I2C_CLIENT_INSMOD;
210
211Note that you *have* to call the two defined variables `normal_i2c' and
212`normal_i2c_range', without any prefix!
213
214
215Probing classes (sensors)
216-------------------------
217
218If you write a `sensors' driver, you use a slightly different interface.
219As well as I2C addresses, we have to cope with ISA addresses. Also, we
220use a enum of chip types. Don't forget to include `sensors.h'.
221
222The following lists are used internally. They are all lists of integers.
223
224 normal_i2c: filled in by the module writer. Terminated by SENSORS_I2C_END.
225 A list of I2C addresses which should normally be examined.
226 normal_i2c_range: filled in by the module writer. Terminated by
227 SENSORS_I2C_END
228 A list of pairs of I2C addresses, each pair being an inclusive range of
229 addresses which should normally be examined.
230 normal_isa: filled in by the module writer. Terminated by SENSORS_ISA_END.
231 A list of ISA addresses which should normally be examined.
232 normal_isa_range: filled in by the module writer. Terminated by
233 SENSORS_ISA_END
234 A list of triples. The first two elements are ISA addresses, being an
235 range of addresses which should normally be examined. The third is the
236 modulo parameter: only addresses which are 0 module this value relative
237 to the first address of the range are actually considered.
238 probe: insmod parameter. Initialize this list with SENSORS_I2C_END values.
239 A list of pairs. The first value is a bus number (SENSORS_ISA_BUS for
240 the ISA bus, -1 for any I2C bus), the second is the address. These
241 addresses are also probed, as if they were in the 'normal' list.
242 probe_range: insmod parameter. Initialize this list with SENSORS_I2C_END
243 values.
244 A list of triples. The first value is a bus number (SENSORS_ISA_BUS for
245 the ISA bus, -1 for any I2C bus), the second and third are addresses.
246 These form an inclusive range of addresses that are also probed, as
247 if they were in the 'normal' list.
248 ignore: insmod parameter. Initialize this list with SENSORS_I2C_END values.
249 A list of pairs. The first value is a bus number (SENSORS_ISA_BUS for
250 the ISA bus, -1 for any I2C bus), the second is the I2C address. These
251 addresses are never probed. This parameter overrules 'normal' and
252 'probe', but not the 'force' lists.
253 ignore_range: insmod parameter. Initialize this list with SENSORS_I2C_END
254 values.
255 A list of triples. The first value is a bus number (SENSORS_ISA_BUS for
256 the ISA bus, -1 for any I2C bus), the second and third are addresses.
257 These form an inclusive range of I2C addresses that are never probed.
258 This parameter overrules 'normal' and 'probe', but not the 'force' lists.
259
260Also used is a list of pointers to sensors_force_data structures:
261 force_data: insmod parameters. A list, ending with an element of which
262 the force field is NULL.
263 Each element contains the type of chip and a list of pairs.
264 The first value is a bus number (SENSORS_ISA_BUS for the ISA bus,
265 -1 for any I2C bus), the second is the address.
266 These are automatically translated to insmod variables of the form
267 force_foo.
268
269So we have a generic insmod variabled `force', and chip-specific variables
270`force_CHIPNAME'.
271
272Fortunately, as a module writer, you just have to define the `normal'
273and/or `normal_range' parameters, and define what chip names are used.
274The complete declaration could look like this:
275 /* Scan i2c addresses 0x20 to 0x2f, 0x37, and 0x40 to 0x4f
276 static unsigned short normal_i2c[] = {0x37,SENSORS_I2C_END};
277 static unsigned short normal_i2c_range[] = {0x20,0x2f,0x40,0x4f,
278 SENSORS_I2C_END};
279 /* Scan ISA address 0x290 */
280 static unsigned int normal_isa[] = {0x0290,SENSORS_ISA_END};
281 static unsigned int normal_isa_range[] = {SENSORS_ISA_END};
282
283 /* Define chips foo and bar, as well as all module parameters and things */
284 SENSORS_INSMOD_2(foo,bar);
285
286If you have one chip, you use macro SENSORS_INSMOD_1(chip), if you have 2
287you use macro SENSORS_INSMOD_2(chip1,chip2), etc. If you do not want to
288bother with chip types, you can use SENSORS_INSMOD_0.
289
290A enum is automatically defined as follows:
291 enum chips { any_chip, chip1, chip2, ... }
292
293
294Attaching to an adapter
295-----------------------
296
297Whenever a new adapter is inserted, or for all adapters if the driver is
298being registered, the callback attach_adapter() is called. Now is the
299time to determine what devices are present on the adapter, and to register
300a client for each of them.
301
302The attach_adapter callback is really easy: we just call the generic
303detection function. This function will scan the bus for us, using the
304information as defined in the lists explained above. If a device is
305detected at a specific address, another callback is called.
306
307 int foo_attach_adapter(struct i2c_adapter *adapter)
308 {
309 return i2c_probe(adapter,&addr_data,&foo_detect_client);
310 }
311
312For `sensors' drivers, use the i2c_detect function instead:
313
314 int foo_attach_adapter(struct i2c_adapter *adapter)
315 {
316 return i2c_detect(adapter,&addr_data,&foo_detect_client);
317 }
318
319Remember, structure `addr_data' is defined by the macros explained above,
320so you do not have to define it yourself.
321
322The i2c_probe or i2c_detect function will call the foo_detect_client
323function only for those i2c addresses that actually have a device on
324them (unless a `force' parameter was used). In addition, addresses that
325are already in use (by some other registered client) are skipped.
326
327
328The detect client function
329--------------------------
330
331The detect client function is called by i2c_probe or i2c_detect.
332The `kind' parameter contains 0 if this call is due to a `force'
333parameter, and -1 otherwise (for i2c_detect, it contains 0 if
334this call is due to the generic `force' parameter, and the chip type
335number if it is due to a specific `force' parameter).
336
337Below, some things are only needed if this is a `sensors' driver. Those
338parts are between /* SENSORS ONLY START */ and /* SENSORS ONLY END */
339markers.
340
341This function should only return an error (any value != 0) if there is
342some reason why no more detection should be done anymore. If the
343detection just fails for this address, return 0.
344
345For now, you can ignore the `flags' parameter. It is there for future use.
346
347 int foo_detect_client(struct i2c_adapter *adapter, int address,
348 unsigned short flags, int kind)
349 {
350 int err = 0;
351 int i;
352 struct i2c_client *new_client;
353 struct foo_data *data;
354 const char *client_name = ""; /* For non-`sensors' drivers, put the real
355 name here! */
356
357 /* Let's see whether this adapter can support what we need.
358 Please substitute the things you need here!
359 For `sensors' drivers, add `! is_isa &&' to the if statement */
360 if (!i2c_check_functionality(adapter,I2C_FUNC_SMBUS_WORD_DATA |
361 I2C_FUNC_SMBUS_WRITE_BYTE))
362 goto ERROR0;
363
364 /* SENSORS ONLY START */
365 const char *type_name = "";
366 int is_isa = i2c_is_isa_adapter(adapter);
367
368 if (is_isa) {
369
370 /* If this client can't be on the ISA bus at all, we can stop now
371 (call `goto ERROR0'). But for kicks, we will assume it is all
372 right. */
373
374 /* Discard immediately if this ISA range is already used */
375 if (check_region(address,FOO_EXTENT))
376 goto ERROR0;
377
378 /* Probe whether there is anything on this address.
379 Some example code is below, but you will have to adapt this
380 for your own driver */
381
382 if (kind < 0) /* Only if no force parameter was used */ {
383 /* We may need long timeouts at least for some chips. */
384 #define REALLY_SLOW_IO
385 i = inb_p(address + 1);
386 if (inb_p(address + 2) != i)
387 goto ERROR0;
388 if (inb_p(address + 3) != i)
389 goto ERROR0;
390 if (inb_p(address + 7) != i)
391 goto ERROR0;
392 #undef REALLY_SLOW_IO
393
394 /* Let's just hope nothing breaks here */
395 i = inb_p(address + 5) & 0x7f;
396 outb_p(~i & 0x7f,address+5);
397 if ((inb_p(address + 5) & 0x7f) != (~i & 0x7f)) {
398 outb_p(i,address+5);
399 return 0;
400 }
401 }
402 }
403
404 /* SENSORS ONLY END */
405
406 /* OK. For now, we presume we have a valid client. We now create the
407 client structure, even though we cannot fill it completely yet.
408 But it allows us to access several i2c functions safely */
409
410 /* Note that we reserve some space for foo_data too. If you don't
411 need it, remove it. We do it here to help to lessen memory
412 fragmentation. */
413 if (! (new_client = kmalloc(sizeof(struct i2c_client) +
414 sizeof(struct foo_data),
415 GFP_KERNEL))) {
416 err = -ENOMEM;
417 goto ERROR0;
418 }
419
420 /* This is tricky, but it will set the data to the right value. */
421 client->data = new_client + 1;
422 data = (struct foo_data *) (client->data);
423
424 new_client->addr = address;
425 new_client->data = data;
426 new_client->adapter = adapter;
427 new_client->driver = &foo_driver;
428 new_client->flags = 0;
429
430 /* Now, we do the remaining detection. If no `force' parameter is used. */
431
432 /* First, the generic detection (if any), that is skipped if any force
433 parameter was used. */
434 if (kind < 0) {
435 /* The below is of course bogus */
436 if (foo_read(new_client,FOO_REG_GENERIC) != FOO_GENERIC_VALUE)
437 goto ERROR1;
438 }
439
440 /* SENSORS ONLY START */
441
442 /* Next, specific detection. This is especially important for `sensors'
443 devices. */
444
445 /* Determine the chip type. Not needed if a `force_CHIPTYPE' parameter
446 was used. */
447 if (kind <= 0) {
448 i = foo_read(new_client,FOO_REG_CHIPTYPE);
449 if (i == FOO_TYPE_1)
450 kind = chip1; /* As defined in the enum */
451 else if (i == FOO_TYPE_2)
452 kind = chip2;
453 else {
454 printk("foo: Ignoring 'force' parameter for unknown chip at "
455 "adapter %d, address 0x%02x\n",i2c_adapter_id(adapter),address);
456 goto ERROR1;
457 }
458 }
459
460 /* Now set the type and chip names */
461 if (kind == chip1) {
462 type_name = "chip1"; /* For /proc entry */
463 client_name = "CHIP 1";
464 } else if (kind == chip2) {
465 type_name = "chip2"; /* For /proc entry */
466 client_name = "CHIP 2";
467 }
468
469 /* Reserve the ISA region */
470 if (is_isa)
471 request_region(address,FOO_EXTENT,type_name);
472
473 /* SENSORS ONLY END */
474
475 /* Fill in the remaining client fields. */
476 strcpy(new_client->name,client_name);
477
478 /* SENSORS ONLY BEGIN */
479 data->type = kind;
480 /* SENSORS ONLY END */
481
482 data->valid = 0; /* Only if you use this field */
483 init_MUTEX(&data->update_lock); /* Only if you use this field */
484
485 /* Any other initializations in data must be done here too. */
486
487 /* Tell the i2c layer a new client has arrived */
488 if ((err = i2c_attach_client(new_client)))
489 goto ERROR3;
490
491 /* SENSORS ONLY BEGIN */
492 /* Register a new directory entry with module sensors. See below for
493 the `template' structure. */
494 if ((i = i2c_register_entry(new_client, type_name,
495 foo_dir_table_template,THIS_MODULE)) < 0) {
496 err = i;
497 goto ERROR4;
498 }
499 data->sysctl_id = i;
500
501 /* SENSORS ONLY END */
502
503 /* This function can write default values to the client registers, if
504 needed. */
505 foo_init_client(new_client);
506 return 0;
507
508 /* OK, this is not exactly good programming practice, usually. But it is
509 very code-efficient in this case. */
510
511 ERROR4:
512 i2c_detach_client(new_client);
513 ERROR3:
514 ERROR2:
515 /* SENSORS ONLY START */
516 if (is_isa)
517 release_region(address,FOO_EXTENT);
518 /* SENSORS ONLY END */
519 ERROR1:
520 kfree(new_client);
521 ERROR0:
522 return err;
523 }
524
525
526Removing the client
527===================
528
529The detach_client call back function is called when a client should be
530removed. It may actually fail, but only when panicking. This code is
531much simpler than the attachment code, fortunately!
532
533 int foo_detach_client(struct i2c_client *client)
534 {
535 int err,i;
536
537 /* SENSORS ONLY START */
538 /* Deregister with the `i2c-proc' module. */
539 i2c_deregister_entry(((struct lm78_data *)(client->data))->sysctl_id);
540 /* SENSORS ONLY END */
541
542 /* Try to detach the client from i2c space */
543 if ((err = i2c_detach_client(client))) {
544 printk("foo.o: Client deregistration failed, client not detached.\n");
545 return err;
546 }
547
548 /* SENSORS ONLY START */
549 if i2c_is_isa_client(client)
550 release_region(client->addr,LM78_EXTENT);
551 /* SENSORS ONLY END */
552
553 kfree(client); /* Frees client data too, if allocated at the same time */
554 return 0;
555 }
556
557
558Initializing the module or kernel
559=================================
560
561When the kernel is booted, or when your foo driver module is inserted,
562you have to do some initializing. Fortunately, just attaching (registering)
563the driver module is usually enough.
564
565 /* Keep track of how far we got in the initialization process. If several
566 things have to initialized, and we fail halfway, only those things
567 have to be cleaned up! */
568 static int __initdata foo_initialized = 0;
569
570 static int __init foo_init(void)
571 {
572 int res;
573 printk("foo version %s (%s)\n",FOO_VERSION,FOO_DATE);
574
575 if ((res = i2c_add_driver(&foo_driver))) {
576 printk("foo: Driver registration failed, module not inserted.\n");
577 foo_cleanup();
578 return res;
579 }
580 foo_initialized ++;
581 return 0;
582 }
583
584 void foo_cleanup(void)
585 {
586 if (foo_initialized == 1) {
587 if ((res = i2c_del_driver(&foo_driver))) {
588 printk("foo: Driver registration failed, module not removed.\n");
589 return;
590 }
591 foo_initialized --;
592 }
593 }
594
595 /* Substitute your own name and email address */
596 MODULE_AUTHOR("Frodo Looijaard <frodol@dds.nl>"
597 MODULE_DESCRIPTION("Driver for Barf Inc. Foo I2C devices");
598
599 module_init(foo_init);
600 module_exit(foo_cleanup);
601
602Note that some functions are marked by `__init', and some data structures
603by `__init_data'. Hose functions and structures can be removed after
604kernel booting (or module loading) is completed.
605
606Command function
607================
608
609A generic ioctl-like function call back is supported. You will seldom
610need this. You may even set it to NULL.
611
612 /* No commands defined */
613 int foo_command(struct i2c_client *client, unsigned int cmd, void *arg)
614 {
615 return 0;
616 }
617
618
619Sending and receiving
620=====================
621
622If you want to communicate with your device, there are several functions
623to do this. You can find all of them in i2c.h.
624
625If you can choose between plain i2c communication and SMBus level
626communication, please use the last. All adapters understand SMBus level
627commands, but only some of them understand plain i2c!
628
629
630Plain i2c communication
631-----------------------
632
633 extern int i2c_master_send(struct i2c_client *,const char* ,int);
634 extern int i2c_master_recv(struct i2c_client *,char* ,int);
635
636These routines read and write some bytes from/to a client. The client
637contains the i2c address, so you do not have to include it. The second
638parameter contains the bytes the read/write, the third the length of the
639buffer. Returned is the actual number of bytes read/written.
640
641 extern int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msg,
642 int num);
643
644This sends a series of messages. Each message can be a read or write,
645and they can be mixed in any way. The transactions are combined: no
646stop bit is sent between transaction. The i2c_msg structure contains
647for each message the client address, the number of bytes of the message
648and the message data itself.
649
650You can read the file `i2c-protocol' for more information about the
651actual i2c protocol.
652
653
654SMBus communication
655-------------------
656
657 extern s32 i2c_smbus_xfer (struct i2c_adapter * adapter, u16 addr,
658 unsigned short flags,
659 char read_write, u8 command, int size,
660 union i2c_smbus_data * data);
661
662 This is the generic SMBus function. All functions below are implemented
663 in terms of it. Never use this function directly!
664
665
666 extern s32 i2c_smbus_write_quick(struct i2c_client * client, u8 value);
667 extern s32 i2c_smbus_read_byte(struct i2c_client * client);
668 extern s32 i2c_smbus_write_byte(struct i2c_client * client, u8 value);
669 extern s32 i2c_smbus_read_byte_data(struct i2c_client * client, u8 command);
670 extern s32 i2c_smbus_write_byte_data(struct i2c_client * client,
671 u8 command, u8 value);
672 extern s32 i2c_smbus_read_word_data(struct i2c_client * client, u8 command);
673 extern s32 i2c_smbus_write_word_data(struct i2c_client * client,
674 u8 command, u16 value);
675 extern s32 i2c_smbus_write_block_data(struct i2c_client * client,
676 u8 command, u8 length,
677 u8 *values);
678
679These ones were removed in Linux 2.6.10 because they had no users, but could
680be added back later if needed:
681
682 extern s32 i2c_smbus_read_i2c_block_data(struct i2c_client * client,
683 u8 command, u8 *values);
684 extern s32 i2c_smbus_read_block_data(struct i2c_client * client,
685 u8 command, u8 *values);
686 extern s32 i2c_smbus_write_i2c_block_data(struct i2c_client * client,
687 u8 command, u8 length,
688 u8 *values);
689 extern s32 i2c_smbus_process_call(struct i2c_client * client,
690 u8 command, u16 value);
691 extern s32 i2c_smbus_block_process_call(struct i2c_client *client,
692 u8 command, u8 length,
693 u8 *values)
694
695All these transactions return -1 on failure. The 'write' transactions
696return 0 on success; the 'read' transactions return the read value, except
697for read_block, which returns the number of values read. The block buffers
698need not be longer than 32 bytes.
699
700You can read the file `smbus-protocol' for more information about the
701actual SMBus protocol.
702
703
704General purpose routines
705========================
706
707Below all general purpose routines are listed, that were not mentioned
708before.
709
710 /* This call returns a unique low identifier for each registered adapter,
711 * or -1 if the adapter was not registered.
712 */
713 extern int i2c_adapter_id(struct i2c_adapter *adap);
714
715
716The sensors sysctl/proc interface
717=================================
718
719This section only applies if you write `sensors' drivers.
720
721Each sensors driver creates a directory in /proc/sys/dev/sensors for each
722registered client. The directory is called something like foo-i2c-4-65.
723The sensors module helps you to do this as easily as possible.
724
725The template
726------------
727
728You will need to define a ctl_table template. This template will automatically
729be copied to a newly allocated structure and filled in where necessary when
730you call sensors_register_entry.
731
732First, I will give an example definition.
733 static ctl_table foo_dir_table_template[] = {
734 { FOO_SYSCTL_FUNC1, "func1", NULL, 0, 0644, NULL, &i2c_proc_real,
735 &i2c_sysctl_real,NULL,&foo_func },
736 { FOO_SYSCTL_FUNC2, "func2", NULL, 0, 0644, NULL, &i2c_proc_real,
737 &i2c_sysctl_real,NULL,&foo_func },
738 { FOO_SYSCTL_DATA, "data", NULL, 0, 0644, NULL, &i2c_proc_real,
739 &i2c_sysctl_real,NULL,&foo_data },
740 { 0 }
741 };
742
743In the above example, three entries are defined. They can either be
744accessed through the /proc interface, in the /proc/sys/dev/sensors/*
745directories, as files named func1, func2 and data, or alternatively
746through the sysctl interface, in the appropriate table, with identifiers
747FOO_SYSCTL_FUNC1, FOO_SYSCTL_FUNC2 and FOO_SYSCTL_DATA.
748
749The third, sixth and ninth parameters should always be NULL, and the
750fourth should always be 0. The fifth is the mode of the /proc file;
7510644 is safe, as the file will be owned by root:root.
752
753The seventh and eighth parameters should be &i2c_proc_real and
754&i2c_sysctl_real if you want to export lists of reals (scaled
755integers). You can also use your own function for them, as usual.
756Finally, the last parameter is the call-back to gather the data
757(see below) if you use the *_proc_real functions.
758
759
760Gathering the data
761------------------
762
763The call back functions (foo_func and foo_data in the above example)
764can be called in several ways; the operation parameter determines
765what should be done:
766
767 * If operation == SENSORS_PROC_REAL_INFO, you must return the
768 magnitude (scaling) in nrels_mag;
769 * If operation == SENSORS_PROC_REAL_READ, you must read information
770 from the chip and return it in results. The number of integers
771 to display should be put in nrels_mag;
772 * If operation == SENSORS_PROC_REAL_WRITE, you must write the
773 supplied information to the chip. nrels_mag will contain the number
774 of integers, results the integers themselves.
775
776The *_proc_real functions will display the elements as reals for the
777/proc interface. If you set the magnitude to 2, and supply 345 for
778SENSORS_PROC_REAL_READ, it would display 3.45; and if the user would
779write 45.6 to the /proc file, it would be returned as 4560 for
780SENSORS_PROC_REAL_WRITE. A magnitude may even be negative!
781
782An example function:
783
784 /* FOO_FROM_REG and FOO_TO_REG translate between scaled values and
785 register values. Note the use of the read cache. */
786 void foo_in(struct i2c_client *client, int operation, int ctl_name,
787 int *nrels_mag, long *results)
788 {
789 struct foo_data *data = client->data;
790 int nr = ctl_name - FOO_SYSCTL_FUNC1; /* reduce to 0 upwards */
791
792 if (operation == SENSORS_PROC_REAL_INFO)
793 *nrels_mag = 2;
794 else if (operation == SENSORS_PROC_REAL_READ) {
795 /* Update the readings cache (if necessary) */
796 foo_update_client(client);
797 /* Get the readings from the cache */
798 results[0] = FOO_FROM_REG(data->foo_func_base[nr]);
799 results[1] = FOO_FROM_REG(data->foo_func_more[nr]);
800 results[2] = FOO_FROM_REG(data->foo_func_readonly[nr]);
801 *nrels_mag = 2;
802 } else if (operation == SENSORS_PROC_REAL_WRITE) {
803 if (*nrels_mag >= 1) {
804 /* Update the cache */
805 data->foo_base[nr] = FOO_TO_REG(results[0]);
806 /* Update the chip */
807 foo_write_value(client,FOO_REG_FUNC_BASE(nr),data->foo_base[nr]);
808 }
809 if (*nrels_mag >= 2) {
810 /* Update the cache */
811 data->foo_more[nr] = FOO_TO_REG(results[1]);
812 /* Update the chip */
813 foo_write_value(client,FOO_REG_FUNC_MORE(nr),data->foo_more[nr]);
814 }
815 }
816 }