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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 .flags = I2C_DF_NOTIFY,
31 .attach_adapter = &foo_attach_adapter,
32 .detach_client = &foo_detach_client,
33 .command = &foo_command /* may be NULL */
34}
35
36The name can be chosen freely, and may be upto 40 characters long. Please
37use something descriptive here.
38
39Don't worry about the flags field; just put I2C_DF_NOTIFY into it. This
40means that your driver will be notified when new adapters are found.
41This is almost always what you want.
42
43All other fields are for call-back functions which will be explained
44below.
45
46There use to be two additional fields in this structure, inc_use et dec_use,
47for module usage count, but these fields were obsoleted and removed.
48
49
50Extra client data
51=================
52
53The client structure has a special `data' field that can point to any
54structure at all. You can use this to keep client-specific data. You
55do not always need this, but especially for `sensors' drivers, it can
56be very useful.
57
58An example structure is below.
59
60 struct foo_data {
61 struct semaphore lock; /* For ISA access in `sensors' drivers. */
62 int sysctl_id; /* To keep the /proc directory entry for
63 `sensors' drivers. */
64 enum chips type; /* To keep the chips type for `sensors' drivers. */
65
66 /* Because the i2c bus is slow, it is often useful to cache the read
67 information of a chip for some time (for example, 1 or 2 seconds).
68 It depends of course on the device whether this is really worthwhile
69 or even sensible. */
70 struct semaphore update_lock; /* When we are reading lots of information,
71 another process should not update the
72 below information */
73 char valid; /* != 0 if the following fields are valid. */
74 unsigned long last_updated; /* In jiffies */
75 /* Add the read information here too */
76 };
77
78
79Accessing the client
80====================
81
82Let's say we have a valid client structure. At some time, we will need
83to gather information from the client, or write new information to the
84client. How we will export this information to user-space is less
85important at this moment (perhaps we do not need to do this at all for
86some obscure clients). But we need generic reading and writing routines.
87
88I have found it useful to define foo_read and foo_write function for this.
89For some cases, it will be easier to call the i2c functions directly,
90but many chips have some kind of register-value idea that can easily
91be encapsulated. Also, some chips have both ISA and I2C interfaces, and
92it useful to abstract from this (only for `sensors' drivers).
93
94The below functions are simple examples, and should not be copied
95literally.
96
97 int foo_read_value(struct i2c_client *client, u8 reg)
98 {
99 if (reg < 0x10) /* byte-sized register */
100 return i2c_smbus_read_byte_data(client,reg);
101 else /* word-sized register */
102 return i2c_smbus_read_word_data(client,reg);
103 }
104
105 int foo_write_value(struct i2c_client *client, u8 reg, u16 value)
106 {
107 if (reg == 0x10) /* Impossible to write - driver error! */ {
108 return -1;
109 else if (reg < 0x10) /* byte-sized register */
110 return i2c_smbus_write_byte_data(client,reg,value);
111 else /* word-sized register */
112 return i2c_smbus_write_word_data(client,reg,value);
113 }
114
115For sensors code, you may have to cope with ISA registers too. Something
116like the below often works. Note the locking!
117
118 int foo_read_value(struct i2c_client *client, u8 reg)
119 {
120 int res;
121 if (i2c_is_isa_client(client)) {
122 down(&(((struct foo_data *) (client->data)) -> lock));
123 outb_p(reg,client->addr + FOO_ADDR_REG_OFFSET);
124 res = inb_p(client->addr + FOO_DATA_REG_OFFSET);
125 up(&(((struct foo_data *) (client->data)) -> lock));
126 return res;
127 } else
128 return i2c_smbus_read_byte_data(client,reg);
129 }
130
131Writing is done the same way.
132
133
134Probing and attaching
135=====================
136
137Most i2c devices can be present on several i2c addresses; for some this
138is determined in hardware (by soldering some chip pins to Vcc or Ground),
139for others this can be changed in software (by writing to specific client
140registers). Some devices are usually on a specific address, but not always;
141and some are even more tricky. So you will probably need to scan several
142i2c addresses for your clients, and do some sort of detection to see
143whether it is actually a device supported by your driver.
144
145To give the user a maximum of possibilities, some default module parameters
146are defined to help determine what addresses are scanned. Several macros
147are defined in i2c.h to help you support them, as well as a generic
148detection algorithm.
149
150You do not have to use this parameter interface; but don't try to use
151function i2c_probe() (or i2c_detect()) if you don't.
152
153NOTE: If you want to write a `sensors' driver, the interface is slightly
154 different! See below.
155
156
157
158Probing classes (i2c)
159---------------------
160
161All parameters are given as lists of unsigned 16-bit integers. Lists are
162terminated by I2C_CLIENT_END.
163The following lists are used internally:
164
165 normal_i2c: filled in by the module writer.
166 A list of I2C addresses which should normally be examined.
167 probe: insmod parameter.
168 A list of pairs. The first value is a bus number (-1 for any I2C bus),
169 the second is the address. These addresses are also probed, as if they
170 were in the 'normal' list.
171 ignore: insmod parameter.
172 A list of pairs. The first value is a bus number (-1 for any I2C bus),
173 the second is the I2C address. These addresses are never probed.
174 This parameter overrules 'normal' and 'probe', but not the 'force' lists.
175 force: insmod parameter.
176 A list of pairs. The first value is a bus number (-1 for any I2C bus),
177 the second is the I2C address. A device is blindly assumed to be on
178 the given address, no probing is done.
179
180Fortunately, as a module writer, you just have to define the `normal_i2c'
181parameter. The complete declaration could look like this:
182
183 /* 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 };
186
187 /* Magic definition of all other variables and things */
188 I2C_CLIENT_INSMOD;
189
190Note that you *have* to call the defined variable `normal_i2c',
191without any prefix!
192
193
194Probing classes (sensors)
195-------------------------
196
197If you write a `sensors' driver, you use a slightly different interface.
198Also, we use a enum of chip types. Don't forget to include `sensors.h'.
199
200The following lists are used internally. They are all lists of integers.
201
202 normal_i2c: filled in by the module writer. Terminated by I2C_CLIENT_END.
203 A list of I2C addresses which should normally be examined.
204 probe: insmod parameter. Initialize this list with I2C_CLIENT_END values.
205 A list of pairs. The first value is a bus number (ANY_I2C_BUS for any
206 I2C bus), the second is the address. These addresses are also probed,
207 as if they were in the 'normal' list.
208 ignore: insmod parameter. Initialize this list with I2C_CLIENT_END values.
209 A list of pairs. The first value is a bus number (ANY_I2C_BUS for any
210 I2C bus), the second is the I2C address. These addresses are never
211 probed. This parameter overrules 'normal' and 'probe', but not the
212 'force' lists.
213
214Also used is a list of pointers to sensors_force_data structures:
215 force_data: insmod parameters. A list, ending with an element of which
216 the force field is NULL.
217 Each element contains the type of chip and a list of pairs.
218 The first value is a bus number (ANY_I2C_BUS for any I2C bus), the
219 second is the address.
220 These are automatically translated to insmod variables of the form
221 force_foo.
222
223So we have a generic insmod variabled `force', and chip-specific variables
224`force_CHIPNAME'.
225
226Fortunately, as a module writer, you just have to define the `normal_i2c'
227parameter, and define what chip names are used. The complete declaration
228could look like this:
229 /* Scan i2c addresses 0x37, and 0x48 to 0x4f */
230 static unsigned short normal_i2c[] = { 0x37, 0x48, 0x49, 0x4a, 0x4b, 0x4c,
231 0x4d, 0x4e, 0x4f, I2C_CLIENT_END };
232
233 /* Define chips foo and bar, as well as all module parameters and things */
234 SENSORS_INSMOD_2(foo,bar);
235
236If you have one chip, you use macro SENSORS_INSMOD_1(chip), if you have 2
237you use macro SENSORS_INSMOD_2(chip1,chip2), etc. If you do not want to
238bother with chip types, you can use SENSORS_INSMOD_0.
239
240A enum is automatically defined as follows:
241 enum chips { any_chip, chip1, chip2, ... }
242
243
244Attaching to an adapter
245-----------------------
246
247Whenever a new adapter is inserted, or for all adapters if the driver is
248being registered, the callback attach_adapter() is called. Now is the
249time to determine what devices are present on the adapter, and to register
250a client for each of them.
251
252The attach_adapter callback is really easy: we just call the generic
253detection function. This function will scan the bus for us, using the
254information as defined in the lists explained above. If a device is
255detected at a specific address, another callback is called.
256
257 int foo_attach_adapter(struct i2c_adapter *adapter)
258 {
259 return i2c_probe(adapter,&addr_data,&foo_detect_client);
260 }
261
262For `sensors' drivers, use the i2c_detect function instead:
263
264 int foo_attach_adapter(struct i2c_adapter *adapter)
265 {
266 return i2c_detect(adapter,&addr_data,&foo_detect_client);
267 }
268
269Remember, structure `addr_data' is defined by the macros explained above,
270so you do not have to define it yourself.
271
272The i2c_probe or i2c_detect function will call the foo_detect_client
273function only for those i2c addresses that actually have a device on
274them (unless a `force' parameter was used). In addition, addresses that
275are already in use (by some other registered client) are skipped.
276
277
278The detect client function
279--------------------------
280
281The detect client function is called by i2c_probe or i2c_detect.
282The `kind' parameter contains 0 if this call is due to a `force'
283parameter, and -1 otherwise (for i2c_detect, it contains 0 if
284this call is due to the generic `force' parameter, and the chip type
285number if it is due to a specific `force' parameter).
286
287Below, some things are only needed if this is a `sensors' driver. Those
288parts are between /* SENSORS ONLY START */ and /* SENSORS ONLY END */
289markers.
290
291This function should only return an error (any value != 0) if there is
292some reason why no more detection should be done anymore. If the
293detection just fails for this address, return 0.
294
295For now, you can ignore the `flags' parameter. It is there for future use.
296
297 int foo_detect_client(struct i2c_adapter *adapter, int address,
298 unsigned short flags, int kind)
299 {
300 int err = 0;
301 int i;
302 struct i2c_client *new_client;
303 struct foo_data *data;
304 const char *client_name = ""; /* For non-`sensors' drivers, put the real
305 name here! */
306
307 /* Let's see whether this adapter can support what we need.
308 Please substitute the things you need here!
309 For `sensors' drivers, add `! is_isa &&' to the if statement */
310 if (!i2c_check_functionality(adapter,I2C_FUNC_SMBUS_WORD_DATA |
311 I2C_FUNC_SMBUS_WRITE_BYTE))
312 goto ERROR0;
313
314 /* SENSORS ONLY START */
315 const char *type_name = "";
316 int is_isa = i2c_is_isa_adapter(adapter);
317
318 /* Do this only if the chip can additionally be found on the ISA bus
319 (hybrid chip). */
320
321 if (is_isa) {
322
323 /* Discard immediately if this ISA range is already used */
324 if (check_region(address,FOO_EXTENT))
325 goto ERROR0;
326
327 /* Probe whether there is anything on this address.
328 Some example code is below, but you will have to adapt this
329 for your own driver */
330
331 if (kind < 0) /* Only if no force parameter was used */ {
332 /* We may need long timeouts at least for some chips. */
333 #define REALLY_SLOW_IO
334 i = inb_p(address + 1);
335 if (inb_p(address + 2) != i)
336 goto ERROR0;
337 if (inb_p(address + 3) != i)
338 goto ERROR0;
339 if (inb_p(address + 7) != i)
340 goto ERROR0;
341 #undef REALLY_SLOW_IO
342
343 /* Let's just hope nothing breaks here */
344 i = inb_p(address + 5) & 0x7f;
345 outb_p(~i & 0x7f,address+5);
346 if ((inb_p(address + 5) & 0x7f) != (~i & 0x7f)) {
347 outb_p(i,address+5);
348 return 0;
349 }
350 }
351 }
352
353 /* SENSORS ONLY END */
354
355 /* OK. For now, we presume we have a valid client. We now create the
356 client structure, even though we cannot fill it completely yet.
357 But it allows us to access several i2c functions safely */
358
359 /* Note that we reserve some space for foo_data too. If you don't
360 need it, remove it. We do it here to help to lessen memory
361 fragmentation. */
362 if (! (new_client = kmalloc(sizeof(struct i2c_client) +
363 sizeof(struct foo_data),
364 GFP_KERNEL))) {
365 err = -ENOMEM;
366 goto ERROR0;
367 }
368
369 /* This is tricky, but it will set the data to the right value. */
370 client->data = new_client + 1;
371 data = (struct foo_data *) (client->data);
372
373 new_client->addr = address;
374 new_client->data = data;
375 new_client->adapter = adapter;
376 new_client->driver = &foo_driver;
377 new_client->flags = 0;
378
379 /* Now, we do the remaining detection. If no `force' parameter is used. */
380
381 /* First, the generic detection (if any), that is skipped if any force
382 parameter was used. */
383 if (kind < 0) {
384 /* The below is of course bogus */
385 if (foo_read(new_client,FOO_REG_GENERIC) != FOO_GENERIC_VALUE)
386 goto ERROR1;
387 }
388
389 /* SENSORS ONLY START */
390
391 /* Next, specific detection. This is especially important for `sensors'
392 devices. */
393
394 /* Determine the chip type. Not needed if a `force_CHIPTYPE' parameter
395 was used. */
396 if (kind <= 0) {
397 i = foo_read(new_client,FOO_REG_CHIPTYPE);
398 if (i == FOO_TYPE_1)
399 kind = chip1; /* As defined in the enum */
400 else if (i == FOO_TYPE_2)
401 kind = chip2;
402 else {
403 printk("foo: Ignoring 'force' parameter for unknown chip at "
404 "adapter %d, address 0x%02x\n",i2c_adapter_id(adapter),address);
405 goto ERROR1;
406 }
407 }
408
409 /* Now set the type and chip names */
410 if (kind == chip1) {
411 type_name = "chip1"; /* For /proc entry */
412 client_name = "CHIP 1";
413 } else if (kind == chip2) {
414 type_name = "chip2"; /* For /proc entry */
415 client_name = "CHIP 2";
416 }
417
418 /* Reserve the ISA region */
419 if (is_isa)
420 request_region(address,FOO_EXTENT,type_name);
421
422 /* SENSORS ONLY END */
423
424 /* Fill in the remaining client fields. */
425 strcpy(new_client->name,client_name);
426
427 /* SENSORS ONLY BEGIN */
428 data->type = kind;
429 /* SENSORS ONLY END */
430
431 data->valid = 0; /* Only if you use this field */
432 init_MUTEX(&data->update_lock); /* Only if you use this field */
433
434 /* Any other initializations in data must be done here too. */
435
436 /* Tell the i2c layer a new client has arrived */
437 if ((err = i2c_attach_client(new_client)))
438 goto ERROR3;
439
440 /* SENSORS ONLY BEGIN */
441 /* Register a new directory entry with module sensors. See below for
442 the `template' structure. */
443 if ((i = i2c_register_entry(new_client, type_name,
444 foo_dir_table_template,THIS_MODULE)) < 0) {
445 err = i;
446 goto ERROR4;
447 }
448 data->sysctl_id = i;
449
450 /* SENSORS ONLY END */
451
452 /* This function can write default values to the client registers, if
453 needed. */
454 foo_init_client(new_client);
455 return 0;
456
457 /* OK, this is not exactly good programming practice, usually. But it is
458 very code-efficient in this case. */
459
460 ERROR4:
461 i2c_detach_client(new_client);
462 ERROR3:
463 ERROR2:
464 /* SENSORS ONLY START */
465 if (is_isa)
466 release_region(address,FOO_EXTENT);
467 /* SENSORS ONLY END */
468 ERROR1:
469 kfree(new_client);
470 ERROR0:
471 return err;
472 }
473
474
475Removing the client
476===================
477
478The detach_client call back function is called when a client should be
479removed. It may actually fail, but only when panicking. This code is
480much simpler than the attachment code, fortunately!
481
482 int foo_detach_client(struct i2c_client *client)
483 {
484 int err,i;
485
486 /* SENSORS ONLY START */
487 /* Deregister with the `i2c-proc' module. */
488 i2c_deregister_entry(((struct lm78_data *)(client->data))->sysctl_id);
489 /* SENSORS ONLY END */
490
491 /* Try to detach the client from i2c space */
492 if ((err = i2c_detach_client(client))) {
493 printk("foo.o: Client deregistration failed, client not detached.\n");
494 return err;
495 }
496
497 /* HYBRID SENSORS CHIP ONLY START */
498 if i2c_is_isa_client(client)
499 release_region(client->addr,LM78_EXTENT);
500 /* HYBRID SENSORS CHIP ONLY END */
501
502 kfree(client); /* Frees client data too, if allocated at the same time */
503 return 0;
504 }
505
506
507Initializing the module or kernel
508=================================
509
510When the kernel is booted, or when your foo driver module is inserted,
511you have to do some initializing. Fortunately, just attaching (registering)
512the driver module is usually enough.
513
514 /* Keep track of how far we got in the initialization process. If several
515 things have to initialized, and we fail halfway, only those things
516 have to be cleaned up! */
517 static int __initdata foo_initialized = 0;
518
519 static int __init foo_init(void)
520 {
521 int res;
522 printk("foo version %s (%s)\n",FOO_VERSION,FOO_DATE);
523
524 if ((res = i2c_add_driver(&foo_driver))) {
525 printk("foo: Driver registration failed, module not inserted.\n");
526 foo_cleanup();
527 return res;
528 }
529 foo_initialized ++;
530 return 0;
531 }
532
533 void foo_cleanup(void)
534 {
535 if (foo_initialized == 1) {
536 if ((res = i2c_del_driver(&foo_driver))) {
537 printk("foo: Driver registration failed, module not removed.\n");
538 return;
539 }
540 foo_initialized --;
541 }
542 }
543
544 /* Substitute your own name and email address */
545 MODULE_AUTHOR("Frodo Looijaard <frodol@dds.nl>"
546 MODULE_DESCRIPTION("Driver for Barf Inc. Foo I2C devices");
547
548 module_init(foo_init);
549 module_exit(foo_cleanup);
550
551Note that some functions are marked by `__init', and some data structures
552by `__init_data'. Hose functions and structures can be removed after
553kernel booting (or module loading) is completed.
554
555Command function
556================
557
558A generic ioctl-like function call back is supported. You will seldom
559need this. You may even set it to NULL.
560
561 /* No commands defined */
562 int foo_command(struct i2c_client *client, unsigned int cmd, void *arg)
563 {
564 return 0;
565 }
566
567
568Sending and receiving
569=====================
570
571If you want to communicate with your device, there are several functions
572to do this. You can find all of them in i2c.h.
573
574If you can choose between plain i2c communication and SMBus level
575communication, please use the last. All adapters understand SMBus level
576commands, but only some of them understand plain i2c!
577
578
579Plain i2c communication
580-----------------------
581
582 extern int i2c_master_send(struct i2c_client *,const char* ,int);
583 extern int i2c_master_recv(struct i2c_client *,char* ,int);
584
585These routines read and write some bytes from/to a client. The client
586contains the i2c address, so you do not have to include it. The second
587parameter contains the bytes the read/write, the third the length of the
588buffer. Returned is the actual number of bytes read/written.
589
590 extern int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msg,
591 int num);
592
593This sends a series of messages. Each message can be a read or write,
594and they can be mixed in any way. The transactions are combined: no
595stop bit is sent between transaction. The i2c_msg structure contains
596for each message the client address, the number of bytes of the message
597and the message data itself.
598
599You can read the file `i2c-protocol' for more information about the
600actual i2c protocol.
601
602
603SMBus communication
604-------------------
605
606 extern s32 i2c_smbus_xfer (struct i2c_adapter * adapter, u16 addr,
607 unsigned short flags,
608 char read_write, u8 command, int size,
609 union i2c_smbus_data * data);
610
611 This is the generic SMBus function. All functions below are implemented
612 in terms of it. Never use this function directly!
613
614
615 extern s32 i2c_smbus_write_quick(struct i2c_client * client, u8 value);
616 extern s32 i2c_smbus_read_byte(struct i2c_client * client);
617 extern s32 i2c_smbus_write_byte(struct i2c_client * client, u8 value);
618 extern s32 i2c_smbus_read_byte_data(struct i2c_client * client, u8 command);
619 extern s32 i2c_smbus_write_byte_data(struct i2c_client * client,
620 u8 command, u8 value);
621 extern s32 i2c_smbus_read_word_data(struct i2c_client * client, u8 command);
622 extern s32 i2c_smbus_write_word_data(struct i2c_client * client,
623 u8 command, u16 value);
624 extern s32 i2c_smbus_write_block_data(struct i2c_client * client,
625 u8 command, u8 length,
626 u8 *values);
627
628These ones were removed in Linux 2.6.10 because they had no users, but could
629be added back later if needed:
630
631 extern s32 i2c_smbus_read_i2c_block_data(struct i2c_client * client,
632 u8 command, u8 *values);
633 extern s32 i2c_smbus_read_block_data(struct i2c_client * client,
634 u8 command, u8 *values);
635 extern s32 i2c_smbus_write_i2c_block_data(struct i2c_client * client,
636 u8 command, u8 length,
637 u8 *values);
638 extern s32 i2c_smbus_process_call(struct i2c_client * client,
639 u8 command, u16 value);
640 extern s32 i2c_smbus_block_process_call(struct i2c_client *client,
641 u8 command, u8 length,
642 u8 *values)
643
644All these transactions return -1 on failure. The 'write' transactions
645return 0 on success; the 'read' transactions return the read value, except
646for read_block, which returns the number of values read. The block buffers
647need not be longer than 32 bytes.
648
649You can read the file `smbus-protocol' for more information about the
650actual SMBus protocol.
651
652
653General purpose routines
654========================
655
656Below all general purpose routines are listed, that were not mentioned
657before.
658
659 /* This call returns a unique low identifier for each registered adapter,
660 * or -1 if the adapter was not registered.
661 */
662 extern int i2c_adapter_id(struct i2c_adapter *adap);
663
664
665The sensors sysctl/proc interface
666=================================
667
668This section only applies if you write `sensors' drivers.
669
670Each sensors driver creates a directory in /proc/sys/dev/sensors for each
671registered client. The directory is called something like foo-i2c-4-65.
672The sensors module helps you to do this as easily as possible.
673
674The template
675------------
676
677You will need to define a ctl_table template. This template will automatically
678be copied to a newly allocated structure and filled in where necessary when
679you call sensors_register_entry.
680
681First, I will give an example definition.
682 static ctl_table foo_dir_table_template[] = {
683 { FOO_SYSCTL_FUNC1, "func1", NULL, 0, 0644, NULL, &i2c_proc_real,
684 &i2c_sysctl_real,NULL,&foo_func },
685 { FOO_SYSCTL_FUNC2, "func2", NULL, 0, 0644, NULL, &i2c_proc_real,
686 &i2c_sysctl_real,NULL,&foo_func },
687 { FOO_SYSCTL_DATA, "data", NULL, 0, 0644, NULL, &i2c_proc_real,
688 &i2c_sysctl_real,NULL,&foo_data },
689 { 0 }
690 };
691
692In the above example, three entries are defined. They can either be
693accessed through the /proc interface, in the /proc/sys/dev/sensors/*
694directories, as files named func1, func2 and data, or alternatively
695through the sysctl interface, in the appropriate table, with identifiers
696FOO_SYSCTL_FUNC1, FOO_SYSCTL_FUNC2 and FOO_SYSCTL_DATA.
697
698The third, sixth and ninth parameters should always be NULL, and the
699fourth should always be 0. The fifth is the mode of the /proc file;
7000644 is safe, as the file will be owned by root:root.
701
702The seventh and eighth parameters should be &i2c_proc_real and
703&i2c_sysctl_real if you want to export lists of reals (scaled
704integers). You can also use your own function for them, as usual.
705Finally, the last parameter is the call-back to gather the data
706(see below) if you use the *_proc_real functions.
707
708
709Gathering the data
710------------------
711
712The call back functions (foo_func and foo_data in the above example)
713can be called in several ways; the operation parameter determines
714what should be done:
715
716 * If operation == SENSORS_PROC_REAL_INFO, you must return the
717 magnitude (scaling) in nrels_mag;
718 * If operation == SENSORS_PROC_REAL_READ, you must read information
719 from the chip and return it in results. The number of integers
720 to display should be put in nrels_mag;
721 * If operation == SENSORS_PROC_REAL_WRITE, you must write the
722 supplied information to the chip. nrels_mag will contain the number
723 of integers, results the integers themselves.
724
725The *_proc_real functions will display the elements as reals for the
726/proc interface. If you set the magnitude to 2, and supply 345 for
727SENSORS_PROC_REAL_READ, it would display 3.45; and if the user would
728write 45.6 to the /proc file, it would be returned as 4560 for
729SENSORS_PROC_REAL_WRITE. A magnitude may even be negative!
730
731An example function:
732
733 /* FOO_FROM_REG and FOO_TO_REG translate between scaled values and
734 register values. Note the use of the read cache. */
735 void foo_in(struct i2c_client *client, int operation, int ctl_name,
736 int *nrels_mag, long *results)
737 {
738 struct foo_data *data = client->data;
739 int nr = ctl_name - FOO_SYSCTL_FUNC1; /* reduce to 0 upwards */
740
741 if (operation == SENSORS_PROC_REAL_INFO)
742 *nrels_mag = 2;
743 else if (operation == SENSORS_PROC_REAL_READ) {
744 /* Update the readings cache (if necessary) */
745 foo_update_client(client);
746 /* Get the readings from the cache */
747 results[0] = FOO_FROM_REG(data->foo_func_base[nr]);
748 results[1] = FOO_FROM_REG(data->foo_func_more[nr]);
749 results[2] = FOO_FROM_REG(data->foo_func_readonly[nr]);
750 *nrels_mag = 2;
751 } else if (operation == SENSORS_PROC_REAL_WRITE) {
752 if (*nrels_mag >= 1) {
753 /* Update the cache */
754 data->foo_base[nr] = FOO_TO_REG(results[0]);
755 /* Update the chip */
756 foo_write_value(client,FOO_REG_FUNC_BASE(nr),data->foo_base[nr]);
757 }
758 if (*nrels_mag >= 2) {
759 /* Update the cache */
760 data->foo_more[nr] = FOO_TO_REG(results[1]);
761 /* Update the chip */
762 foo_write_value(client,FOO_REG_FUNC_MORE(nr),data->foo_more[nr]);
763 }
764 }
765 }