1 This is a small guide for those who want to write kernel drivers for I2C
4 To set up a driver, you need to do several things. Some are optional, and
5 some things can be done slightly or completely different. Use this as a
6 guide, not as a rule book!
12 Try to keep the kernel namespace as clean as possible. The best way to
13 do this is to use a unique prefix for all global symbols. This is
14 especially important for exported symbols, but it is a good idea to do
15 it for non-exported symbols too. We will use the prefix `foo_' in this
16 tutorial, and `FOO_' for preprocessor variables.
22 Usually, you will implement a single driver structure, and instantiate
23 all clients from it. Remember, a driver structure contains general access
24 routines, a client structure specific information like the actual I2C
27 static struct i2c_driver foo_driver = {
28 .name = "Foo version 2.3 driver",
29 .id = I2C_DRIVERID_FOO, /* from i2c-id.h, optional */
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 .inc_use = foo_inc_use, /* May be NULL */
35 .dec_use = foo_dec_use, /* May be NULL */
38 The name can be chosen freely, and may be up to 31 characters long. Please
39 use something descriptive here.
41 If used, the id should be a unique ID. The range 0xf000 to 0xffff is
42 reserved for local use, and you can use one of those until you start
43 distributing the driver, at which time you should contact the i2c authors
44 to get your own ID(s). Note that most of the time you don't need an ID
45 at all so you can just omit it.
47 Don't worry about the flags field; just put I2C_DF_NOTIFY into it. This
48 means that your driver will be notified when new adapters are found.
49 This is almost always what you want.
51 All other fields are for call-back functions which will be explained
58 If your driver can also be compiled as a module, there are moments at
59 which the module can not be removed from memory. For example, when you
60 are doing a lengthy transaction, or when you create a /proc directory,
61 and some process has entered that directory (this last case is the
62 main reason why these call-backs were introduced).
64 To increase or decrease the module usage count, you can use the
65 MOD_{INC,DEC}_USE_COUNT macros. They must be called from the module
66 which needs to get its usage count changed; that is why each driver
67 module has to implement its own callback functions.
69 static void foo_inc_use (struct i2c_client *client)
76 static void foo_dec_use (struct i2c_client *client)
83 Do not call these callback functions directly; instead, use the
84 following functions defined in i2c.h:
86 void i2c_inc_use_client(struct i2c_client *);
87 void i2c_dec_use_client(struct i2c_client *);
89 You should *not* increase the module count just because a device is
90 detected and a client created. This would make it impossible to remove
97 The client structure has a special `data' field that can point to any
98 structure at all. You can use this to keep client-specific data. You
99 do not always need this, but especially for `sensors' drivers, it can
102 An example structure is below.
105 struct semaphore lock; /* For ISA access in `sensors' drivers. */
106 int sysctl_id; /* To keep the /proc directory entry for
107 `sensors' drivers. */
108 enum chips type; /* To keep the chips type for `sensors' drivers. */
110 /* Because the i2c bus is slow, it is often useful to cache the read
111 information of a chip for some time (for example, 1 or 2 seconds).
112 It depends of course on the device whether this is really worthwhile
114 struct semaphore update_lock; /* When we are reading lots of information,
115 another process should not update the
117 char valid; /* != 0 if the following fields are valid. */
118 unsigned long last_updated; /* In jiffies */
119 /* Add the read information here too */
126 Let's say we have a valid client structure. At some time, we will need
127 to gather information from the client, or write new information to the
128 client. How we will export this information to user-space is less
129 important at this moment (perhaps we do not need to do this at all for
130 some obscure clients). But we need generic reading and writing routines.
132 I have found it useful to define foo_read and foo_write function for this.
133 For some cases, it will be easier to call the i2c functions directly,
134 but many chips have some kind of register-value idea that can easily
135 be encapsulated. Also, some chips have both ISA and I2C interfaces, and
136 it useful to abstract from this (only for `sensors' drivers).
138 The below functions are simple examples, and should not be copied
141 int foo_read_value(struct i2c_client *client, u8 reg)
143 if (reg < 0x10) /* byte-sized register */
144 return i2c_smbus_read_byte_data(client,reg);
145 else /* word-sized register */
146 return i2c_smbus_read_word_data(client,reg);
149 int foo_write_value(struct i2c_client *client, u8 reg, u16 value)
151 if (reg == 0x10) /* Impossible to write - driver error! */ {
153 else if (reg < 0x10) /* byte-sized register */
154 return i2c_smbus_write_byte_data(client,reg,value);
155 else /* word-sized register */
156 return i2c_smbus_write_word_data(client,reg,value);
159 For sensors code, you may have to cope with ISA registers too. Something
160 like the below often works. Note the locking!
162 int foo_read_value(struct i2c_client *client, u8 reg)
165 if (i2c_is_isa_client(client)) {
166 down(&(((struct foo_data *) (client->data)) -> lock));
167 outb_p(reg,client->addr + FOO_ADDR_REG_OFFSET);
168 res = inb_p(client->addr + FOO_DATA_REG_OFFSET);
169 up(&(((struct foo_data *) (client->data)) -> lock));
172 return i2c_smbus_read_byte_data(client,reg);
175 Writing is done the same way.
178 Probing and attaching
179 =====================
181 Most i2c devices can be present on several i2c addresses; for some this
182 is determined in hardware (by soldering some chip pins to Vcc or Ground),
183 for others this can be changed in software (by writing to specific client
184 registers). Some devices are usually on a specific address, but not always;
185 and some are even more tricky. So you will probably need to scan several
186 i2c addresses for your clients, and do some sort of detection to see
187 whether it is actually a device supported by your driver.
189 To give the user a maximum of possibilities, some default module parameters
190 are defined to help determine what addresses are scanned. Several macros
191 are defined in i2c.h to help you support them, as well as a generic
194 You do not have to use this parameter interface; but don't try to use
195 function i2c_probe() (or i2c_detect()) if you don't.
197 NOTE: If you want to write a `sensors' driver, the interface is slightly
198 different! See below.
202 Probing classes (i2c)
203 ---------------------
205 All parameters are given as lists of unsigned 16-bit integers. Lists are
206 terminated by I2C_CLIENT_END.
207 The following lists are used internally:
209 normal_i2c: filled in by the module writer.
210 A list of I2C addresses which should normally be examined.
211 normal_i2c_range: filled in by the module writer.
212 A list of pairs of I2C addresses, each pair being an inclusive range of
213 addresses which should normally be examined.
214 probe: insmod parameter.
215 A list of pairs. The first value is a bus number (-1 for any I2C bus),
216 the second is the address. These addresses are also probed, as if they
217 were in the 'normal' list.
218 probe_range: insmod parameter.
219 A list of triples. The first value is a bus number (-1 for any I2C bus),
220 the second and third are addresses. These form an inclusive range of
221 addresses that are also probed, as if they were in the 'normal' list.
222 ignore: insmod parameter.
223 A list of pairs. The first value is a bus number (-1 for any I2C bus),
224 the second is the I2C address. These addresses are never probed.
225 This parameter overrules 'normal' and 'probe', but not the 'force' lists.
226 ignore_range: insmod parameter.
227 A list of triples. The first value is a bus number (-1 for any I2C bus),
228 the second and third are addresses. These form an inclusive range of
229 I2C addresses that are never probed.
230 This parameter overrules 'normal' and 'probe', but not the 'force' lists.
231 force: insmod parameter.
232 A list of pairs. The first value is a bus number (-1 for any I2C bus),
233 the second is the I2C address. A device is blindly assumed to be on
234 the given address, no probing is done.
236 Fortunately, as a module writer, you just have to define the `normal'
237 and/or `normal_range' parameters. The complete declaration could look
240 /* Scan 0x20 to 0x2f, 0x37, and 0x40 to 0x4f */
241 static unsigned short normal_i2c[] = { 0x37,I2C_CLIENT_END };
242 static unsigned short normal_i2c_range[] = { 0x20, 0x2f, 0x40, 0x4f,
245 /* Magic definition of all other variables and things */
248 Note that you *have* to call the two defined variables `normal_i2c' and
249 `normal_i2c_range', without any prefix!
252 Probing classes (sensors)
253 -------------------------
255 If you write a `sensors' driver, you use a slightly different interface.
256 As well as I2C addresses, we have to cope with ISA addresses. Also, we
257 use a enum of chip types. Don't forget to include `sensors.h'.
259 The following lists are used internally. They are all lists of integers.
261 normal_i2c: filled in by the module writer. Terminated by SENSORS_I2C_END.
262 A list of I2C addresses which should normally be examined.
263 normal_i2c_range: filled in by the module writer. Terminated by
265 A list of pairs of I2C addresses, each pair being an inclusive range of
266 addresses which should normally be examined.
267 normal_isa: filled in by the module writer. Terminated by SENSORS_ISA_END.
268 A list of ISA addresses which should normally be examined.
269 normal_isa_range: filled in by the module writer. Terminated by
271 A list of triples. The first two elements are ISA addresses, being an
272 range of addresses which should normally be examined. The third is the
273 modulo parameter: only addresses which are 0 module this value relative
274 to the first address of the range are actually considered.
275 probe: insmod parameter. Initialize this list with SENSORS_I2C_END values.
276 A list of pairs. The first value is a bus number (SENSORS_ISA_BUS for
277 the ISA bus, -1 for any I2C bus), the second is the address. These
278 addresses are also probed, as if they were in the 'normal' list.
279 probe_range: insmod parameter. Initialize this list with SENSORS_I2C_END
281 A list of triples. The first value is a bus number (SENSORS_ISA_BUS for
282 the ISA bus, -1 for any I2C bus), the second and third are addresses.
283 These form an inclusive range of addresses that are also probed, as
284 if they were in the 'normal' list.
285 ignore: insmod parameter. Initialize this list with SENSORS_I2C_END values.
286 A list of pairs. The first value is a bus number (SENSORS_ISA_BUS for
287 the ISA bus, -1 for any I2C bus), the second is the I2C address. These
288 addresses are never probed. This parameter overrules 'normal' and
289 'probe', but not the 'force' lists.
290 ignore_range: insmod parameter. Initialize this list with SENSORS_I2C_END
292 A list of triples. The first value is a bus number (SENSORS_ISA_BUS for
293 the ISA bus, -1 for any I2C bus), the second and third are addresses.
294 These form an inclusive range of I2C addresses that are never probed.
295 This parameter overrules 'normal' and 'probe', but not the 'force' lists.
297 Also used is a list of pointers to sensors_force_data structures:
298 force_data: insmod parameters. A list, ending with an element of which
299 the force field is NULL.
300 Each element contains the type of chip and a list of pairs.
301 The first value is a bus number (SENSORS_ISA_BUS for the ISA bus,
302 -1 for any I2C bus), the second is the address.
303 These are automatically translated to insmod variables of the form
306 So we have a generic insmod variable `force', and chip-specific variables
309 Fortunately, as a module writer, you just have to define the `normal'
310 and/or `normal_range' parameters, and define what chip names are used.
311 The complete declaration could look like this:
312 /* Scan i2c addresses 0x20 to 0x2f, 0x37, and 0x40 to 0x4f
313 static unsigned short normal_i2c[] = {0x37,SENSORS_I2C_END};
314 static unsigned short normal_i2c_range[] = {0x20,0x2f,0x40,0x4f,
316 /* Scan ISA address 0x290 */
317 static unsigned int normal_isa[] = {0x0290,SENSORS_ISA_END};
318 static unsigned int normal_isa_range[] = {SENSORS_ISA_END};
320 /* Define chips foo and bar, as well as all module parameters and things */
321 SENSORS_INSMOD_2(foo,bar);
323 If you have one chip, you use macro SENSORS_INSMOD_1(chip), if you have 2
324 you use macro SENSORS_INSMOD_2(chip1,chip2), etc. If you do not want to
325 bother with chip types, you can use SENSORS_INSMOD_0.
327 A enum is automatically defined as follows:
328 enum chips { any_chip, chip1, chip2, ... }
331 Attaching to an adapter
332 -----------------------
334 Whenever a new adapter is inserted, or for all adapters if the driver is
335 being registered, the callback attach_adapter() is called. Now is the
336 time to determine what devices are present on the adapter, and to register
337 a client for each of them.
339 The attach_adapter callback is really easy: we just call the generic
340 detection function. This function will scan the bus for us, using the
341 information as defined in the lists explained above. If a device is
342 detected at a specific address, another callback is called.
344 int foo_attach_adapter(struct i2c_adapter *adapter)
346 return i2c_probe(adapter,&addr_data,&foo_detect_client);
349 For `sensors' drivers, use the i2c_detect function instead:
351 int foo_attach_adapter(struct i2c_adapter *adapter)
353 return i2c_detect(adapter,&addr_data,&foo_detect_client);
356 Remember, structure `addr_data' is defined by the macros explained above,
357 so you do not have to define it yourself.
359 The i2c_probe or i2c_detect function will call the foo_detect_client
360 function only for those i2c addresses that actually have a device on
361 them (unless a `force' parameter was used). In addition, addresses that
362 are already in use (by some other registered client) are skipped.
365 The detect client function
366 --------------------------
368 The detect client function is called by i2c_probe or i2c_detect.
369 The `kind' parameter contains 0 if this call is due to a `force'
370 parameter, and -1 otherwise (for i2c_detect, it contains 0 if
371 this call is due to the generic `force' parameter, and the chip type
372 number if it is due to a specific `force' parameter).
374 Below, some things are only needed if this is a `sensors' driver. Those
375 parts are between /* SENSORS ONLY START */ and /* SENSORS ONLY END */
378 This function should only return an error (any value != 0) if there is
379 some reason why no more detection should be done anymore. If the
380 detection just fails for this address, return 0.
382 For now, you can ignore the `flags' parameter. It is there for future use.
384 int foo_detect_client(struct i2c_adapter *adapter, int address,
385 unsigned short flags, int kind)
389 struct i2c_client *new_client;
390 struct foo_data *data;
391 const char *client_name = ""; /* For non-`sensors' drivers, put the real
394 /* Let's see whether this adapter can support what we need.
395 Please substitute the things you need here!
396 For `sensors' drivers, add `! is_isa &&' to the if statement */
397 if (!i2c_check_functionality(adapter,I2C_FUNC_SMBUS_WORD_DATA |
398 I2C_FUNC_SMBUS_WRITE_BYTE))
401 /* SENSORS ONLY START */
402 const char *type_name = "";
403 int is_isa = i2c_is_isa_adapter(adapter);
407 /* If this client can't be on the ISA bus at all, we can stop now
408 (call `goto ERROR0'). But for kicks, we will assume it is all
411 /* Discard immediately if this ISA range is already used */
412 if (check_region(address,FOO_EXTENT))
415 /* Probe whether there is anything on this address.
416 Some example code is below, but you will have to adapt this
417 for your own driver */
419 if (kind < 0) /* Only if no force parameter was used */ {
420 /* We may need long timeouts at least for some chips. */
421 #define REALLY_SLOW_IO
422 i = inb_p(address + 1);
423 if (inb_p(address + 2) != i)
425 if (inb_p(address + 3) != i)
427 if (inb_p(address + 7) != i)
429 #undef REALLY_SLOW_IO
431 /* Let's just hope nothing breaks here */
432 i = inb_p(address + 5) & 0x7f;
433 outb_p(~i & 0x7f,address+5);
434 if ((inb_p(address + 5) & 0x7f) != (~i & 0x7f)) {
441 /* SENSORS ONLY END */
443 /* OK. For now, we presume we have a valid client. We now create the
444 client structure, even though we cannot fill it completely yet.
445 But it allows us to access several i2c functions safely */
447 /* Note that we reserve some space for foo_data too. If you don't
448 need it, remove it. We do it here to help to lessen memory
450 if (! (new_client = kmalloc(sizeof(struct i2c_client) +
451 sizeof(struct foo_data),
457 /* This is tricky, but it will set the data to the right value. */
458 client->data = new_client + 1;
459 data = (struct foo_data *) (client->data);
461 new_client->addr = address;
462 new_client->data = data;
463 new_client->adapter = adapter;
464 new_client->driver = &foo_driver;
465 new_client->flags = 0;
467 /* Now, we do the remaining detection. If no `force' parameter is used. */
469 /* First, the generic detection (if any), that is skipped if any force
470 parameter was used. */
472 /* The below is of course bogus */
473 if (foo_read(new_client,FOO_REG_GENERIC) != FOO_GENERIC_VALUE)
477 /* SENSORS ONLY START */
479 /* Next, specific detection. This is especially important for `sensors'
482 /* Determine the chip type. Not needed if a `force_CHIPTYPE' parameter
485 i = foo_read(new_client,FOO_REG_CHIPTYPE);
487 kind = chip1; /* As defined in the enum */
488 else if (i == FOO_TYPE_2)
491 printk("foo: Ignoring 'force' parameter for unknown chip at "
492 "adapter %d, address 0x%02x\n",i2c_adapter_id(adapter),address);
497 /* Now set the type and chip names */
499 type_name = "chip1"; /* For /proc entry */
500 client_name = "CHIP 1";
501 } else if (kind == chip2) {
502 type_name = "chip2"; /* For /proc entry */
503 client_name = "CHIP 2";
506 /* Reserve the ISA region */
508 request_region(address,FOO_EXTENT,type_name);
510 /* SENSORS ONLY END */
512 /* Fill in the remaining client fields. */
513 strcpy(new_client->name,client_name);
515 /* SENSORS ONLY BEGIN */
517 /* SENSORS ONLY END */
519 data->valid = 0; /* Only if you use this field */
520 init_MUTEX(&data->update_lock); /* Only if you use this field */
522 /* Any other initializations in data must be done here too. */
524 /* Tell the i2c layer a new client has arrived */
525 if ((err = i2c_attach_client(new_client)))
528 /* SENSORS ONLY BEGIN */
529 /* Register a new directory entry with module sensors. See below for
530 the `template' structure. */
531 if ((i = i2c_register_entry(new_client, type_name,
532 foo_dir_table_template,THIS_MODULE)) < 0) {
538 /* SENSORS ONLY END */
540 /* This function can write default values to the client registers, if
542 foo_init_client(new_client);
545 /* OK, this is not exactly good programming practice, usually. But it is
546 very code-efficient in this case. */
549 i2c_detach_client(new_client);
552 /* SENSORS ONLY START */
554 release_region(address,FOO_EXTENT);
555 /* SENSORS ONLY END */
566 The detach_client call back function is called when a client should be
567 removed. It may actually fail, but only when panicking. This code is
568 much simpler than the attachment code, fortunately!
570 int foo_detach_client(struct i2c_client *client)
574 /* SENSORS ONLY START */
575 /* Deregister with the `i2c-proc' module. */
576 i2c_deregister_entry(((struct lm78_data *)(client->data))->sysctl_id);
577 /* SENSORS ONLY END */
579 /* Try to detach the client from i2c space */
580 if ((err = i2c_detach_client(client))) {
581 printk("foo.o: Client deregistration failed, client not detached.\n");
585 /* SENSORS ONLY START */
586 if i2c_is_isa_client(client)
587 release_region(client->addr,LM78_EXTENT);
588 /* SENSORS ONLY END */
590 kfree(client); /* Frees client data too, if allocated at the same time */
595 Initializing the module or kernel
596 =================================
598 When the kernel is booted, or when your foo driver module is inserted,
599 you have to do some initializing. Fortunately, just attaching (registering)
600 the driver module is usually enough.
602 /* Keep track of how far we got in the initialization process. If several
603 things have to initialized, and we fail halfway, only those things
604 have to be cleaned up! */
605 static int __initdata foo_initialized = 0;
607 int __init foo_init(void)
610 printk("foo version %s (%s)\n",FOO_VERSION,FOO_DATE);
612 if ((res = i2c_add_driver(&foo_driver))) {
613 printk("foo: Driver registration failed, module not inserted.\n");
621 int __init foo_cleanup(void)
624 if (foo_initialized == 1) {
625 if ((res = i2c_del_driver(&foo_driver))) {
626 printk("foo: Driver registration failed, module not removed.\n");
636 /* Substitute your own name and email address */
637 MODULE_AUTHOR("Frodo Looijaard <frodol@dds.nl>"
638 MODULE_DESCRIPTION("Driver for Barf Inc. Foo I2C devices");
640 int init_module(void)
645 int cleanup_module(void)
647 return foo_cleanup();
650 #endif /* def MODULE */
652 Note that some functions are marked by `__init', and some data structures
653 by `__init_data'. If this driver is compiled as part of the kernel (instead
654 of as a module), those functions and structures can be removed after
655 kernel booting is completed.
660 A generic ioctl-like function call back is supported. You will seldom
661 need this. You may even set it to NULL.
663 /* No commands defined */
664 int foo_command(struct i2c_client *client, unsigned int cmd, void *arg)
670 Sending and receiving
671 =====================
673 If you want to communicate with your device, there are several functions
674 to do this. You can find all of them in i2c.h.
676 If you can choose between plain i2c communication and SMBus level
677 communication, please use the last. All adapters understand SMBus level
678 commands, but only some of them understand plain i2c!
681 Plain i2c communication
682 -----------------------
684 extern int i2c_master_send(struct i2c_client *,const char* ,int);
685 extern int i2c_master_recv(struct i2c_client *,char* ,int);
687 These routines read and write some bytes from/to a client. The client
688 contains the i2c address, so you do not have to include it. The second
689 parameter contains the bytes the read/write, the third the length of the
690 buffer. Returned is the actual number of bytes read/written.
692 extern int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg msg[],
695 This sends a series of messages. Each message can be a read or write,
696 and they can be mixed in any way. The transactions are combined: no
697 stop bit is sent between transaction. The i2c_msg structure contains
698 for each message the client address, the number of bytes of the message
699 and the message data itself.
701 You can read the file `i2c-protocol' for more information about the
708 extern s32 i2c_smbus_xfer (struct i2c_adapter * adapter, u16 addr,
709 unsigned short flags,
710 char read_write, u8 command, int size,
711 union i2c_smbus_data * data);
713 This is the generic SMBus function. All functions below are implemented
714 in terms of it. Never use this function directly!
717 extern s32 i2c_smbus_write_quick(struct i2c_client * client, u8 value);
718 extern s32 i2c_smbus_read_byte(struct i2c_client * client);
719 extern s32 i2c_smbus_write_byte(struct i2c_client * client, u8 value);
720 extern s32 i2c_smbus_read_byte_data(struct i2c_client * client, u8 command);
721 extern s32 i2c_smbus_write_byte_data(struct i2c_client * client,
722 u8 command, u8 value);
723 extern s32 i2c_smbus_read_word_data(struct i2c_client * client, u8 command);
724 extern s32 i2c_smbus_write_word_data(struct i2c_client * client,
725 u8 command, u16 value);
726 extern s32 i2c_smbus_process_call(struct i2c_client * client,
727 u8 command, u16 value);
728 extern s32 i2c_smbus_read_block_data(struct i2c_client * client,
729 u8 command, u8 *values);
730 extern s32 i2c_smbus_write_block_data(struct i2c_client * client,
731 u8 command, u8 length,
734 All these transactions return -1 on failure. The 'write' transactions
735 return 0 on success; the 'read' transactions return the read value, except
736 for read_block, which returns the number of values read. The block buffers
737 need not be longer than 32 bytes.
739 You can read the file `smbus-protocol' for more information about the
740 actual SMBus protocol.
743 General purpose routines
744 ========================
746 Below all general purpose routines are listed, that were not mentioned
749 /* This call returns a unique low identifier for each registered adapter,
750 * or -1 if the adapter was not registered.
752 extern int i2c_adapter_id(struct i2c_adapter *adap);
755 The sensors sysctl/proc interface
756 =================================
758 This section only applies if you write `sensors' drivers.
760 Each sensors driver creates a directory in /proc/sys/dev/sensors for each
761 registered client. The directory is called something like foo-i2c-4-65.
762 The sensors module helps you to do this as easily as possible.
767 You will need to define a ctl_table template. This template will automatically
768 be copied to a newly allocated structure and filled in where necessary when
769 you call sensors_register_entry.
771 First, I will give an example definition.
772 static ctl_table foo_dir_table_template[] = {
773 { FOO_SYSCTL_FUNC1, "func1", NULL, 0, 0644, NULL, &i2c_proc_real,
774 &i2c_sysctl_real,NULL,&foo_func },
775 { FOO_SYSCTL_FUNC2, "func2", NULL, 0, 0644, NULL, &i2c_proc_real,
776 &i2c_sysctl_real,NULL,&foo_func },
777 { FOO_SYSCTL_DATA, "data", NULL, 0, 0644, NULL, &i2c_proc_real,
778 &i2c_sysctl_real,NULL,&foo_data },
782 In the above example, three entries are defined. They can either be
783 accessed through the /proc interface, in the /proc/sys/dev/sensors/*
784 directories, as files named func1, func2 and data, or alternatively
785 through the sysctl interface, in the appropriate table, with identifiers
786 FOO_SYSCTL_FUNC1, FOO_SYSCTL_FUNC2 and FOO_SYSCTL_DATA.
788 The third, sixth and ninth parameters should always be NULL, and the
789 fourth should always be 0. The fifth is the mode of the /proc file;
790 0644 is safe, as the file will be owned by root:root.
792 The seventh and eighth parameters should be &i2c_proc_real and
793 &i2c_sysctl_real if you want to export lists of reals (scaled
794 integers). You can also use your own function for them, as usual.
795 Finally, the last parameter is the call-back to gather the data
796 (see below) if you use the *_proc_real functions.
802 The call back functions (foo_func and foo_data in the above example)
803 can be called in several ways; the operation parameter determines
806 * If operation == SENSORS_PROC_REAL_INFO, you must return the
807 magnitude (scaling) in nrels_mag;
808 * If operation == SENSORS_PROC_REAL_READ, you must read information
809 from the chip and return it in results. The number of integers
810 to display should be put in nrels_mag;
811 * If operation == SENSORS_PROC_REAL_WRITE, you must write the
812 supplied information to the chip. nrels_mag will contain the number
813 of integers, results the integers themselves.
815 The *_proc_real functions will display the elements as reals for the
816 /proc interface. If you set the magnitude to 2, and supply 345 for
817 SENSORS_PROC_REAL_READ, it would display 3.45; and if the user would
818 write 45.6 to the /proc file, it would be returned as 4560 for
819 SENSORS_PROC_REAL_WRITE. A magnitude may even be negative!
823 /* FOO_FROM_REG and FOO_TO_REG translate between scaled values and
824 register values. Note the use of the read cache. */
825 void foo_in(struct i2c_client *client, int operation, int ctl_name,
826 int *nrels_mag, long *results)
828 struct foo_data *data = client->data;
829 int nr = ctl_name - FOO_SYSCTL_FUNC1; /* reduce to 0 upwards */
831 if (operation == SENSORS_PROC_REAL_INFO)
833 else if (operation == SENSORS_PROC_REAL_READ) {
834 /* Update the readings cache (if necessary) */
835 foo_update_client(client);
836 /* Get the readings from the cache */
837 results[0] = FOO_FROM_REG(data->foo_func_base[nr]);
838 results[1] = FOO_FROM_REG(data->foo_func_more[nr]);
839 results[2] = FOO_FROM_REG(data->foo_func_readonly[nr]);
841 } else if (operation == SENSORS_PROC_REAL_WRITE) {
842 if (*nrels_mag >= 1) {
843 /* Update the cache */
844 data->foo_base[nr] = FOO_TO_REG(results[0]);
845 /* Update the chip */
846 foo_write_value(client,FOO_REG_FUNC_BASE(nr),data->foo_base[nr]);
848 if (*nrels_mag >= 2) {
849 /* Update the cache */
850 data->foo_more[nr] = FOO_TO_REG(results[1]);
851 /* Update the chip */
852 foo_write_value(client,FOO_REG_FUNC_MORE(nr),data->foo_more[nr]);