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 = {
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 */
37 The name can be chosen freely, and may be upto 40 characters long. Please
38 use something descriptive here.
40 If used, the id should be a unique ID. The range 0xf000 to 0xffff is
41 reserved for local use, and you can use one of those until you start
42 distributing the driver, at which time you should contact the i2c authors
43 to get your own ID(s). Note that most of the time you don't need an ID
44 at all so you can just omit it.
46 Don't worry about the flags field; just put I2C_DF_NOTIFY into it. This
47 means that your driver will be notified when new adapters are found.
48 This is almost always what you want.
50 All other fields are for call-back functions which will be explained
53 There use to be two additional fields in this structure, inc_use et dec_use,
54 for module usage count, but these fields were obsoleted and removed.
60 The client structure has a special `data' field that can point to any
61 structure at all. You can use this to keep client-specific data. You
62 do not always need this, but especially for `sensors' drivers, it can
65 An example structure is below.
68 struct semaphore lock; /* For ISA access in `sensors' drivers. */
69 int sysctl_id; /* To keep the /proc directory entry for
71 enum chips type; /* To keep the chips type for `sensors' drivers. */
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
77 struct semaphore update_lock; /* When we are reading lots of information,
78 another process should not update the
80 char valid; /* != 0 if the following fields are valid. */
81 unsigned long last_updated; /* In jiffies */
82 /* Add the read information here too */
89 Let's say we have a valid client structure. At some time, we will need
90 to gather information from the client, or write new information to the
91 client. How we will export this information to user-space is less
92 important at this moment (perhaps we do not need to do this at all for
93 some obscure clients). But we need generic reading and writing routines.
95 I have found it useful to define foo_read and foo_write function for this.
96 For some cases, it will be easier to call the i2c functions directly,
97 but many chips have some kind of register-value idea that can easily
98 be encapsulated. Also, some chips have both ISA and I2C interfaces, and
99 it useful to abstract from this (only for `sensors' drivers).
101 The below functions are simple examples, and should not be copied
104 int foo_read_value(struct i2c_client *client, u8 reg)
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);
112 int foo_write_value(struct i2c_client *client, u8 reg, u16 value)
114 if (reg == 0x10) /* Impossible to write - driver error! */ {
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);
122 For sensors code, you may have to cope with ISA registers too. Something
123 like the below often works. Note the locking!
125 int foo_read_value(struct i2c_client *client, u8 reg)
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));
135 return i2c_smbus_read_byte_data(client,reg);
138 Writing is done the same way.
141 Probing and attaching
142 =====================
144 Most i2c devices can be present on several i2c addresses; for some this
145 is determined in hardware (by soldering some chip pins to Vcc or Ground),
146 for others this can be changed in software (by writing to specific client
147 registers). Some devices are usually on a specific address, but not always;
148 and some are even more tricky. So you will probably need to scan several
149 i2c addresses for your clients, and do some sort of detection to see
150 whether it is actually a device supported by your driver.
152 To give the user a maximum of possibilities, some default module parameters
153 are defined to help determine what addresses are scanned. Several macros
154 are defined in i2c.h to help you support them, as well as a generic
157 You do not have to use this parameter interface; but don't try to use
158 function i2c_probe() (or i2c_detect()) if you don't.
160 NOTE: If you want to write a `sensors' driver, the interface is slightly
161 different! See below.
165 Probing classes (i2c)
166 ---------------------
168 All parameters are given as lists of unsigned 16-bit integers. Lists are
169 terminated by I2C_CLIENT_END.
170 The following lists are used internally:
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.
199 Fortunately, as a module writer, you just have to define the `normal'
200 and/or `normal_range' parameters. The complete declaration could look
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,
208 /* Magic definition of all other variables and things */
211 Note that you *have* to call the two defined variables `normal_i2c' and
212 `normal_i2c_range', without any prefix!
215 Probing classes (sensors)
216 -------------------------
218 If you write a `sensors' driver, you use a slightly different interface.
219 As well as I2C addresses, we have to cope with ISA addresses. Also, we
220 use a enum of chip types. Don't forget to include `sensors.h'.
222 The following lists are used internally. They are all lists of integers.
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
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
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
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
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.
260 Also 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
269 So we have a generic insmod variabled `force', and chip-specific variables
272 Fortunately, as a module writer, you just have to define the `normal'
273 and/or `normal_range' parameters, and define what chip names are used.
274 The 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,
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};
283 /* Define chips foo and bar, as well as all module parameters and things */
284 SENSORS_INSMOD_2(foo,bar);
286 If you have one chip, you use macro SENSORS_INSMOD_1(chip), if you have 2
287 you use macro SENSORS_INSMOD_2(chip1,chip2), etc. If you do not want to
288 bother with chip types, you can use SENSORS_INSMOD_0.
290 A enum is automatically defined as follows:
291 enum chips { any_chip, chip1, chip2, ... }
294 Attaching to an adapter
295 -----------------------
297 Whenever a new adapter is inserted, or for all adapters if the driver is
298 being registered, the callback attach_adapter() is called. Now is the
299 time to determine what devices are present on the adapter, and to register
300 a client for each of them.
302 The attach_adapter callback is really easy: we just call the generic
303 detection function. This function will scan the bus for us, using the
304 information as defined in the lists explained above. If a device is
305 detected at a specific address, another callback is called.
307 int foo_attach_adapter(struct i2c_adapter *adapter)
309 return i2c_probe(adapter,&addr_data,&foo_detect_client);
312 For `sensors' drivers, use the i2c_detect function instead:
314 int foo_attach_adapter(struct i2c_adapter *adapter)
316 return i2c_detect(adapter,&addr_data,&foo_detect_client);
319 Remember, structure `addr_data' is defined by the macros explained above,
320 so you do not have to define it yourself.
322 The i2c_probe or i2c_detect function will call the foo_detect_client
323 function only for those i2c addresses that actually have a device on
324 them (unless a `force' parameter was used). In addition, addresses that
325 are already in use (by some other registered client) are skipped.
328 The detect client function
329 --------------------------
331 The detect client function is called by i2c_probe or i2c_detect.
332 The `kind' parameter contains 0 if this call is due to a `force'
333 parameter, and -1 otherwise (for i2c_detect, it contains 0 if
334 this call is due to the generic `force' parameter, and the chip type
335 number if it is due to a specific `force' parameter).
337 Below, some things are only needed if this is a `sensors' driver. Those
338 parts are between /* SENSORS ONLY START */ and /* SENSORS ONLY END */
341 This function should only return an error (any value != 0) if there is
342 some reason why no more detection should be done anymore. If the
343 detection just fails for this address, return 0.
345 For now, you can ignore the `flags' parameter. It is there for future use.
347 /* Unique ID allocation */
348 static int foo_id = 0;
350 int foo_detect_client(struct i2c_adapter *adapter, int address,
351 unsigned short flags, int kind)
355 struct i2c_client *new_client;
356 struct foo_data *data;
357 const char *client_name = ""; /* For non-`sensors' drivers, put the real
360 /* Let's see whether this adapter can support what we need.
361 Please substitute the things you need here!
362 For `sensors' drivers, add `! is_isa &&' to the if statement */
363 if (!i2c_check_functionality(adapter,I2C_FUNC_SMBUS_WORD_DATA |
364 I2C_FUNC_SMBUS_WRITE_BYTE))
367 /* SENSORS ONLY START */
368 const char *type_name = "";
369 int is_isa = i2c_is_isa_adapter(adapter);
373 /* If this client can't be on the ISA bus at all, we can stop now
374 (call `goto ERROR0'). But for kicks, we will assume it is all
377 /* Discard immediately if this ISA range is already used */
378 if (check_region(address,FOO_EXTENT))
381 /* Probe whether there is anything on this address.
382 Some example code is below, but you will have to adapt this
383 for your own driver */
385 if (kind < 0) /* Only if no force parameter was used */ {
386 /* We may need long timeouts at least for some chips. */
387 #define REALLY_SLOW_IO
388 i = inb_p(address + 1);
389 if (inb_p(address + 2) != i)
391 if (inb_p(address + 3) != i)
393 if (inb_p(address + 7) != i)
395 #undef REALLY_SLOW_IO
397 /* Let's just hope nothing breaks here */
398 i = inb_p(address + 5) & 0x7f;
399 outb_p(~i & 0x7f,address+5);
400 if ((inb_p(address + 5) & 0x7f) != (~i & 0x7f)) {
407 /* SENSORS ONLY END */
409 /* OK. For now, we presume we have a valid client. We now create the
410 client structure, even though we cannot fill it completely yet.
411 But it allows us to access several i2c functions safely */
413 /* Note that we reserve some space for foo_data too. If you don't
414 need it, remove it. We do it here to help to lessen memory
416 if (! (new_client = kmalloc(sizeof(struct i2c_client) +
417 sizeof(struct foo_data),
423 /* This is tricky, but it will set the data to the right value. */
424 client->data = new_client + 1;
425 data = (struct foo_data *) (client->data);
427 new_client->addr = address;
428 new_client->data = data;
429 new_client->adapter = adapter;
430 new_client->driver = &foo_driver;
431 new_client->flags = 0;
433 /* Now, we do the remaining detection. If no `force' parameter is used. */
435 /* First, the generic detection (if any), that is skipped if any force
436 parameter was used. */
438 /* The below is of course bogus */
439 if (foo_read(new_client,FOO_REG_GENERIC) != FOO_GENERIC_VALUE)
443 /* SENSORS ONLY START */
445 /* Next, specific detection. This is especially important for `sensors'
448 /* Determine the chip type. Not needed if a `force_CHIPTYPE' parameter
451 i = foo_read(new_client,FOO_REG_CHIPTYPE);
453 kind = chip1; /* As defined in the enum */
454 else if (i == FOO_TYPE_2)
457 printk("foo: Ignoring 'force' parameter for unknown chip at "
458 "adapter %d, address 0x%02x\n",i2c_adapter_id(adapter),address);
463 /* Now set the type and chip names */
465 type_name = "chip1"; /* For /proc entry */
466 client_name = "CHIP 1";
467 } else if (kind == chip2) {
468 type_name = "chip2"; /* For /proc entry */
469 client_name = "CHIP 2";
472 /* Reserve the ISA region */
474 request_region(address,FOO_EXTENT,type_name);
476 /* SENSORS ONLY END */
478 /* Fill in the remaining client fields. */
479 strcpy(new_client->name,client_name);
481 /* SENSORS ONLY BEGIN */
483 /* SENSORS ONLY END */
485 new_client->id = foo_id++; /* Automatically unique */
486 data->valid = 0; /* Only if you use this field */
487 init_MUTEX(&data->update_lock); /* Only if you use this field */
489 /* Any other initializations in data must be done here too. */
491 /* Tell the i2c layer a new client has arrived */
492 if ((err = i2c_attach_client(new_client)))
495 /* SENSORS ONLY BEGIN */
496 /* Register a new directory entry with module sensors. See below for
497 the `template' structure. */
498 if ((i = i2c_register_entry(new_client, type_name,
499 foo_dir_table_template,THIS_MODULE)) < 0) {
505 /* SENSORS ONLY END */
507 /* This function can write default values to the client registers, if
509 foo_init_client(new_client);
512 /* OK, this is not exactly good programming practice, usually. But it is
513 very code-efficient in this case. */
516 i2c_detach_client(new_client);
519 /* SENSORS ONLY START */
521 release_region(address,FOO_EXTENT);
522 /* SENSORS ONLY END */
533 The detach_client call back function is called when a client should be
534 removed. It may actually fail, but only when panicking. This code is
535 much simpler than the attachment code, fortunately!
537 int foo_detach_client(struct i2c_client *client)
541 /* SENSORS ONLY START */
542 /* Deregister with the `i2c-proc' module. */
543 i2c_deregister_entry(((struct lm78_data *)(client->data))->sysctl_id);
544 /* SENSORS ONLY END */
546 /* Try to detach the client from i2c space */
547 if ((err = i2c_detach_client(client))) {
548 printk("foo.o: Client deregistration failed, client not detached.\n");
552 /* SENSORS ONLY START */
553 if i2c_is_isa_client(client)
554 release_region(client->addr,LM78_EXTENT);
555 /* SENSORS ONLY END */
557 kfree(client); /* Frees client data too, if allocated at the same time */
562 Initializing the module or kernel
563 =================================
565 When the kernel is booted, or when your foo driver module is inserted,
566 you have to do some initializing. Fortunately, just attaching (registering)
567 the driver module is usually enough.
569 /* Keep track of how far we got in the initialization process. If several
570 things have to initialized, and we fail halfway, only those things
571 have to be cleaned up! */
572 static int __initdata foo_initialized = 0;
574 static int __init foo_init(void)
577 printk("foo version %s (%s)\n",FOO_VERSION,FOO_DATE);
579 if ((res = i2c_add_driver(&foo_driver))) {
580 printk("foo: Driver registration failed, module not inserted.\n");
588 void foo_cleanup(void)
590 if (foo_initialized == 1) {
591 if ((res = i2c_del_driver(&foo_driver))) {
592 printk("foo: Driver registration failed, module not removed.\n");
599 /* Substitute your own name and email address */
600 MODULE_AUTHOR("Frodo Looijaard <frodol@dds.nl>"
601 MODULE_DESCRIPTION("Driver for Barf Inc. Foo I2C devices");
603 module_init(foo_init);
604 module_exit(foo_cleanup);
606 Note that some functions are marked by `__init', and some data structures
607 by `__init_data'. Hose functions and structures can be removed after
608 kernel booting (or module loading) is completed.
613 A generic ioctl-like function call back is supported. You will seldom
614 need this. You may even set it to NULL.
616 /* No commands defined */
617 int foo_command(struct i2c_client *client, unsigned int cmd, void *arg)
623 Sending and receiving
624 =====================
626 If you want to communicate with your device, there are several functions
627 to do this. You can find all of them in i2c.h.
629 If you can choose between plain i2c communication and SMBus level
630 communication, please use the last. All adapters understand SMBus level
631 commands, but only some of them understand plain i2c!
634 Plain i2c communication
635 -----------------------
637 extern int i2c_master_send(struct i2c_client *,const char* ,int);
638 extern int i2c_master_recv(struct i2c_client *,char* ,int);
640 These routines read and write some bytes from/to a client. The client
641 contains the i2c address, so you do not have to include it. The second
642 parameter contains the bytes the read/write, the third the length of the
643 buffer. Returned is the actual number of bytes read/written.
645 extern int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg msg[],
648 This sends a series of messages. Each message can be a read or write,
649 and they can be mixed in any way. The transactions are combined: no
650 stop bit is sent between transaction. The i2c_msg structure contains
651 for each message the client address, the number of bytes of the message
652 and the message data itself.
654 You can read the file `i2c-protocol' for more information about the
661 extern s32 i2c_smbus_xfer (struct i2c_adapter * adapter, u16 addr,
662 unsigned short flags,
663 char read_write, u8 command, int size,
664 union i2c_smbus_data * data);
666 This is the generic SMBus function. All functions below are implemented
667 in terms of it. Never use this function directly!
670 extern s32 i2c_smbus_write_quick(struct i2c_client * client, u8 value);
671 extern s32 i2c_smbus_read_byte(struct i2c_client * client);
672 extern s32 i2c_smbus_write_byte(struct i2c_client * client, u8 value);
673 extern s32 i2c_smbus_read_byte_data(struct i2c_client * client, u8 command);
674 extern s32 i2c_smbus_write_byte_data(struct i2c_client * client,
675 u8 command, u8 value);
676 extern s32 i2c_smbus_read_word_data(struct i2c_client * client, u8 command);
677 extern s32 i2c_smbus_write_word_data(struct i2c_client * client,
678 u8 command, u16 value);
679 extern s32 i2c_smbus_write_block_data(struct i2c_client * client,
680 u8 command, u8 length,
683 These ones were removed in Linux 2.6.10 because they had no users, but could
684 be added back later if needed:
686 extern s32 i2c_smbus_read_i2c_block_data(struct i2c_client * client,
687 u8 command, u8 *values);
688 extern s32 i2c_smbus_read_block_data(struct i2c_client * client,
689 u8 command, u8 *values);
690 extern s32 i2c_smbus_write_i2c_block_data(struct i2c_client * client,
691 u8 command, u8 length,
693 extern s32 i2c_smbus_process_call(struct i2c_client * client,
694 u8 command, u16 value);
695 extern s32 i2c_smbus_block_process_call(struct i2c_client *client,
696 u8 command, u8 length,
699 All these transactions return -1 on failure. The 'write' transactions
700 return 0 on success; the 'read' transactions return the read value, except
701 for read_block, which returns the number of values read. The block buffers
702 need not be longer than 32 bytes.
704 You can read the file `smbus-protocol' for more information about the
705 actual SMBus protocol.
708 General purpose routines
709 ========================
711 Below all general purpose routines are listed, that were not mentioned
714 /* This call returns a unique low identifier for each registered adapter,
715 * or -1 if the adapter was not registered.
717 extern int i2c_adapter_id(struct i2c_adapter *adap);
720 The sensors sysctl/proc interface
721 =================================
723 This section only applies if you write `sensors' drivers.
725 Each sensors driver creates a directory in /proc/sys/dev/sensors for each
726 registered client. The directory is called something like foo-i2c-4-65.
727 The sensors module helps you to do this as easily as possible.
732 You will need to define a ctl_table template. This template will automatically
733 be copied to a newly allocated structure and filled in where necessary when
734 you call sensors_register_entry.
736 First, I will give an example definition.
737 static ctl_table foo_dir_table_template[] = {
738 { FOO_SYSCTL_FUNC1, "func1", NULL, 0, 0644, NULL, &i2c_proc_real,
739 &i2c_sysctl_real,NULL,&foo_func },
740 { FOO_SYSCTL_FUNC2, "func2", NULL, 0, 0644, NULL, &i2c_proc_real,
741 &i2c_sysctl_real,NULL,&foo_func },
742 { FOO_SYSCTL_DATA, "data", NULL, 0, 0644, NULL, &i2c_proc_real,
743 &i2c_sysctl_real,NULL,&foo_data },
747 In the above example, three entries are defined. They can either be
748 accessed through the /proc interface, in the /proc/sys/dev/sensors/*
749 directories, as files named func1, func2 and data, or alternatively
750 through the sysctl interface, in the appropriate table, with identifiers
751 FOO_SYSCTL_FUNC1, FOO_SYSCTL_FUNC2 and FOO_SYSCTL_DATA.
753 The third, sixth and ninth parameters should always be NULL, and the
754 fourth should always be 0. The fifth is the mode of the /proc file;
755 0644 is safe, as the file will be owned by root:root.
757 The seventh and eighth parameters should be &i2c_proc_real and
758 &i2c_sysctl_real if you want to export lists of reals (scaled
759 integers). You can also use your own function for them, as usual.
760 Finally, the last parameter is the call-back to gather the data
761 (see below) if you use the *_proc_real functions.
767 The call back functions (foo_func and foo_data in the above example)
768 can be called in several ways; the operation parameter determines
771 * If operation == SENSORS_PROC_REAL_INFO, you must return the
772 magnitude (scaling) in nrels_mag;
773 * If operation == SENSORS_PROC_REAL_READ, you must read information
774 from the chip and return it in results. The number of integers
775 to display should be put in nrels_mag;
776 * If operation == SENSORS_PROC_REAL_WRITE, you must write the
777 supplied information to the chip. nrels_mag will contain the number
778 of integers, results the integers themselves.
780 The *_proc_real functions will display the elements as reals for the
781 /proc interface. If you set the magnitude to 2, and supply 345 for
782 SENSORS_PROC_REAL_READ, it would display 3.45; and if the user would
783 write 45.6 to the /proc file, it would be returned as 4560 for
784 SENSORS_PROC_REAL_WRITE. A magnitude may even be negative!
788 /* FOO_FROM_REG and FOO_TO_REG translate between scaled values and
789 register values. Note the use of the read cache. */
790 void foo_in(struct i2c_client *client, int operation, int ctl_name,
791 int *nrels_mag, long *results)
793 struct foo_data *data = client->data;
794 int nr = ctl_name - FOO_SYSCTL_FUNC1; /* reduce to 0 upwards */
796 if (operation == SENSORS_PROC_REAL_INFO)
798 else if (operation == SENSORS_PROC_REAL_READ) {
799 /* Update the readings cache (if necessary) */
800 foo_update_client(client);
801 /* Get the readings from the cache */
802 results[0] = FOO_FROM_REG(data->foo_func_base[nr]);
803 results[1] = FOO_FROM_REG(data->foo_func_more[nr]);
804 results[2] = FOO_FROM_REG(data->foo_func_readonly[nr]);
806 } else if (operation == SENSORS_PROC_REAL_WRITE) {
807 if (*nrels_mag >= 1) {
808 /* Update the cache */
809 data->foo_base[nr] = FOO_TO_REG(results[0]);
810 /* Update the chip */
811 foo_write_value(client,FOO_REG_FUNC_BASE(nr),data->foo_base[nr]);
813 if (*nrels_mag >= 2) {
814 /* Update the cache */
815 data->foo_more[nr] = FOO_TO_REG(results[1]);
816 /* Update the chip */
817 foo_write_value(client,FOO_REG_FUNC_MORE(nr),data->foo_more[nr]);