1 This is a small guide for those who want to write kernel drivers for I2C
2 or SMBus devices, using Linux as the protocol host/master (not slave).
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, and should be zero-initialized except for fields with data you
25 provide. A client structure holds device-specific information like the
26 driver model device node, and its I2C address.
28 static struct i2c_driver foo_driver = {
33 /* iff driver uses driver model ("new style") binding model: */
37 /* else, driver uses "legacy" binding model: */
38 .attach_adapter = foo_attach_adapter,
39 .detach_client = foo_detach_client,
41 /* these may be used regardless of the driver binding model */
42 .shutdown = foo_shutdown, /* optional */
43 .suspend = foo_suspend, /* optional */
44 .resume = foo_resume, /* optional */
45 .command = foo_command, /* optional */
48 The name field is the driver name, and must not contain spaces. It
49 should match the module name (if the driver can be compiled as a module),
50 although you can use MODULE_ALIAS (passing "foo" in this example) to add
51 another name for the module. If the driver name doesn't match the module
52 name, the module won't be automatically loaded (hotplug/coldplug).
54 All other fields are for call-back functions which will be explained
61 Each client structure has a special `data' field that can point to any
62 structure at all. You should use this to keep device-specific data,
63 especially in drivers that handle multiple I2C or SMBUS devices. You
64 do not always need this, but especially for `sensors' drivers, it can
68 void i2c_set_clientdata(struct i2c_client *client, void *data);
70 /* retrieve the value */
71 void *i2c_get_clientdata(struct i2c_client *client);
73 An example structure is below.
76 struct i2c_client client;
77 struct semaphore lock; /* For ISA access in `sensors' drivers. */
78 int sysctl_id; /* To keep the /proc directory entry for
80 enum chips type; /* To keep the chips type for `sensors' drivers. */
82 /* Because the i2c bus is slow, it is often useful to cache the read
83 information of a chip for some time (for example, 1 or 2 seconds).
84 It depends of course on the device whether this is really worthwhile
86 struct semaphore update_lock; /* When we are reading lots of information,
87 another process should not update the
89 char valid; /* != 0 if the following fields are valid. */
90 unsigned long last_updated; /* In jiffies */
91 /* Add the read information here too */
98 Let's say we have a valid client structure. At some time, we will need
99 to gather information from the client, or write new information to the
100 client. How we will export this information to user-space is less
101 important at this moment (perhaps we do not need to do this at all for
102 some obscure clients). But we need generic reading and writing routines.
104 I have found it useful to define foo_read and foo_write function for this.
105 For some cases, it will be easier to call the i2c functions directly,
106 but many chips have some kind of register-value idea that can easily
107 be encapsulated. Also, some chips have both ISA and I2C interfaces, and
108 it useful to abstract from this (only for `sensors' drivers).
110 The below functions are simple examples, and should not be copied
113 int foo_read_value(struct i2c_client *client, u8 reg)
115 if (reg < 0x10) /* byte-sized register */
116 return i2c_smbus_read_byte_data(client,reg);
117 else /* word-sized register */
118 return i2c_smbus_read_word_data(client,reg);
121 int foo_write_value(struct i2c_client *client, u8 reg, u16 value)
123 if (reg == 0x10) /* Impossible to write - driver error! */ {
125 else if (reg < 0x10) /* byte-sized register */
126 return i2c_smbus_write_byte_data(client,reg,value);
127 else /* word-sized register */
128 return i2c_smbus_write_word_data(client,reg,value);
131 For sensors code, you may have to cope with ISA registers too. Something
132 like the below often works. Note the locking!
134 int foo_read_value(struct i2c_client *client, u8 reg)
137 if (i2c_is_isa_client(client)) {
138 down(&(((struct foo_data *) (client->data)) -> lock));
139 outb_p(reg,client->addr + FOO_ADDR_REG_OFFSET);
140 res = inb_p(client->addr + FOO_DATA_REG_OFFSET);
141 up(&(((struct foo_data *) (client->data)) -> lock));
144 return i2c_smbus_read_byte_data(client,reg);
147 Writing is done the same way.
150 Probing and attaching
151 =====================
153 The Linux I2C stack was originally written to support access to hardware
154 monitoring chips on PC motherboards, and thus it embeds some assumptions
155 that are more appropriate to SMBus (and PCs) than to I2C. One of these
156 assumptions is that most adapters and devices drivers support the SMBUS_QUICK
157 protocol to probe device presence. Another is that devices and their drivers
158 can be sufficiently configured using only such probe primitives.
160 As Linux and its I2C stack became more widely used in embedded systems
161 and complex components such as DVB adapters, those assumptions became more
162 problematic. Drivers for I2C devices that issue interrupts need more (and
163 different) configuration information, as do drivers handling chip variants
164 that can't be distinguished by protocol probing, or which need some board
165 specific information to operate correctly.
167 Accordingly, the I2C stack now has two models for associating I2C devices
168 with their drivers: the original "legacy" model, and a newer one that's
169 fully compatible with the Linux 2.6 driver model. These models do not mix,
170 since the "legacy" model requires drivers to create "i2c_client" device
171 objects after SMBus style probing, while the Linux driver model expects
172 drivers to be given such device objects in their probe() routines.
175 Standard Driver Model Binding ("New Style")
176 -------------------------------------------
178 System infrastructure, typically board-specific initialization code or
179 boot firmware, reports what I2C devices exist. For example, there may be
180 a table, in the kernel or from the boot loader, identifying I2C devices
181 and linking them to board-specific configuration information about IRQs
182 and other wiring artifacts, chip type, and so on. That could be used to
183 create i2c_client objects for each I2C device.
185 I2C device drivers using this binding model work just like any other
186 kind of driver in Linux: they provide a probe() method to bind to
187 those devices, and a remove() method to unbind.
189 static int foo_probe(struct i2c_client *client);
190 static int foo_remove(struct i2c_client *client);
192 Remember that the i2c_driver does not create those client handles. The
193 handle may be used during foo_probe(). If foo_probe() reports success
194 (zero not a negative status code) it may save the handle and use it until
195 foo_remove() returns. That binding model is used by most Linux drivers.
197 Drivers match devices when i2c_client.driver_name and the driver name are
198 the same; this approach is used in several other busses that don't have
199 device typing support in the hardware. The driver and module name should
200 match, so hotplug/coldplug mechanisms will modprobe the driver.
203 Device Creation (Standard driver model)
204 ---------------------------------------
206 If you know for a fact that an I2C device is connected to a given I2C bus,
207 you can instantiate that device by simply filling an i2c_board_info
208 structure with the device address and driver name, and calling
209 i2c_new_device(). This will create the device, then the driver core will
210 take care of finding the right driver and will call its probe() method.
211 If a driver supports different device types, you can specify the type you
212 want using the type field. You can also specify an IRQ and platform data
215 Sometimes you know that a device is connected to a given I2C bus, but you
216 don't know the exact address it uses. This happens on TV adapters for
217 example, where the same driver supports dozens of slightly different
218 models, and I2C device addresses change from one model to the next. In
219 that case, you can use the i2c_new_probed_device() variant, which is
220 similar to i2c_new_device(), except that it takes an additional list of
221 possible I2C addresses to probe. A device is created for the first
222 responsive address in the list. If you expect more than one device to be
223 present in the address range, simply call i2c_new_probed_device() that
226 The call to i2c_new_device() or i2c_new_probed_device() typically happens
227 in the I2C bus driver. You may want to save the returned i2c_client
228 reference for later use.
231 Device Deletion (Standard driver model)
232 ---------------------------------------
234 Each I2C device which has been created using i2c_new_device() or
235 i2c_new_probed_device() can be unregistered by calling
236 i2c_unregister_device(). If you don't call it explicitly, it will be
237 called automatically before the underlying I2C bus itself is removed, as a
238 device can't survive its parent in the device driver model.
241 Legacy Driver Binding Model
242 ---------------------------
244 Most i2c devices can be present on several i2c addresses; for some this
245 is determined in hardware (by soldering some chip pins to Vcc or Ground),
246 for others this can be changed in software (by writing to specific client
247 registers). Some devices are usually on a specific address, but not always;
248 and some are even more tricky. So you will probably need to scan several
249 i2c addresses for your clients, and do some sort of detection to see
250 whether it is actually a device supported by your driver.
252 To give the user a maximum of possibilities, some default module parameters
253 are defined to help determine what addresses are scanned. Several macros
254 are defined in i2c.h to help you support them, as well as a generic
257 You do not have to use this parameter interface; but don't try to use
258 function i2c_probe() if you don't.
260 NOTE: If you want to write a `sensors' driver, the interface is slightly
261 different! See below.
265 Probing classes (Legacy model)
266 ------------------------------
268 All parameters are given as lists of unsigned 16-bit integers. Lists are
269 terminated by I2C_CLIENT_END.
270 The following lists are used internally:
272 normal_i2c: filled in by the module writer.
273 A list of I2C addresses which should normally be examined.
274 probe: insmod parameter.
275 A list of pairs. The first value is a bus number (-1 for any I2C bus),
276 the second is the address. These addresses are also probed, as if they
277 were in the 'normal' list.
278 ignore: insmod parameter.
279 A list of pairs. The first value is a bus number (-1 for any I2C bus),
280 the second is the I2C address. These addresses are never probed.
281 This parameter overrules the 'normal_i2c' list only.
282 force: insmod parameter.
283 A list of pairs. The first value is a bus number (-1 for any I2C bus),
284 the second is the I2C address. A device is blindly assumed to be on
285 the given address, no probing is done.
287 Additionally, kind-specific force lists may optionally be defined if
288 the driver supports several chip kinds. They are grouped in a
289 NULL-terminated list of pointers named forces, those first element if the
290 generic force list mentioned above. Each additional list correspond to an
291 insmod parameter of the form force_<kind>.
293 Fortunately, as a module writer, you just have to define the `normal_i2c'
294 parameter. The complete declaration could look like this:
296 /* Scan 0x37, and 0x48 to 0x4f */
297 static unsigned short normal_i2c[] = { 0x37, 0x48, 0x49, 0x4a, 0x4b, 0x4c,
298 0x4d, 0x4e, 0x4f, I2C_CLIENT_END };
300 /* Magic definition of all other variables and things */
302 /* Or, if your driver supports, say, 2 kind of devices: */
303 I2C_CLIENT_INSMOD_2(foo, bar);
305 If you use the multi-kind form, an enum will be defined for you:
306 enum chips { any_chip, foo, bar, ... }
307 You can then (and certainly should) use it in the driver code.
309 Note that you *have* to call the defined variable `normal_i2c',
313 Attaching to an adapter (Legacy model)
314 --------------------------------------
316 Whenever a new adapter is inserted, or for all adapters if the driver is
317 being registered, the callback attach_adapter() is called. Now is the
318 time to determine what devices are present on the adapter, and to register
319 a client for each of them.
321 The attach_adapter callback is really easy: we just call the generic
322 detection function. This function will scan the bus for us, using the
323 information as defined in the lists explained above. If a device is
324 detected at a specific address, another callback is called.
326 int foo_attach_adapter(struct i2c_adapter *adapter)
328 return i2c_probe(adapter,&addr_data,&foo_detect_client);
331 Remember, structure `addr_data' is defined by the macros explained above,
332 so you do not have to define it yourself.
334 The i2c_probe function will call the foo_detect_client
335 function only for those i2c addresses that actually have a device on
336 them (unless a `force' parameter was used). In addition, addresses that
337 are already in use (by some other registered client) are skipped.
340 The detect client function (Legacy model)
341 -----------------------------------------
343 The detect client function is called by i2c_probe. The `kind' parameter
344 contains -1 for a probed detection, 0 for a forced detection, or a positive
345 number for a forced detection with a chip type forced.
347 Below, some things are only needed if this is a `sensors' driver. Those
348 parts are between /* SENSORS ONLY START */ and /* SENSORS ONLY END */
351 Returning an error different from -ENODEV in a detect function will cause
352 the detection to stop: other addresses and adapters won't be scanned.
353 This should only be done on fatal or internal errors, such as a memory
354 shortage or i2c_attach_client failing.
356 For now, you can ignore the `flags' parameter. It is there for future use.
358 int foo_detect_client(struct i2c_adapter *adapter, int address,
359 unsigned short flags, int kind)
363 struct i2c_client *new_client;
364 struct foo_data *data;
365 const char *client_name = ""; /* For non-`sensors' drivers, put the real
368 /* Let's see whether this adapter can support what we need.
369 Please substitute the things you need here!
370 For `sensors' drivers, add `! is_isa &&' to the if statement */
371 if (!i2c_check_functionality(adapter,I2C_FUNC_SMBUS_WORD_DATA |
372 I2C_FUNC_SMBUS_WRITE_BYTE))
375 /* SENSORS ONLY START */
376 const char *type_name = "";
377 int is_isa = i2c_is_isa_adapter(adapter);
379 /* Do this only if the chip can additionally be found on the ISA bus
384 /* Discard immediately if this ISA range is already used */
385 /* FIXME: never use check_region(), only request_region() */
386 if (check_region(address,FOO_EXTENT))
389 /* Probe whether there is anything on this address.
390 Some example code is below, but you will have to adapt this
391 for your own driver */
393 if (kind < 0) /* Only if no force parameter was used */ {
394 /* We may need long timeouts at least for some chips. */
395 #define REALLY_SLOW_IO
396 i = inb_p(address + 1);
397 if (inb_p(address + 2) != i)
399 if (inb_p(address + 3) != i)
401 if (inb_p(address + 7) != i)
403 #undef REALLY_SLOW_IO
405 /* Let's just hope nothing breaks here */
406 i = inb_p(address + 5) & 0x7f;
407 outb_p(~i & 0x7f,address+5);
408 if ((inb_p(address + 5) & 0x7f) != (~i & 0x7f)) {
415 /* SENSORS ONLY END */
417 /* OK. For now, we presume we have a valid client. We now create the
418 client structure, even though we cannot fill it completely yet.
419 But it allows us to access several i2c functions safely */
421 if (!(data = kzalloc(sizeof(struct foo_data), GFP_KERNEL))) {
426 new_client = &data->client;
427 i2c_set_clientdata(new_client, data);
429 new_client->addr = address;
430 new_client->adapter = adapter;
431 new_client->driver = &foo_driver;
432 new_client->flags = 0;
434 /* Now, we do the remaining detection. If no `force' parameter is used. */
436 /* First, the generic detection (if any), that is skipped if any force
437 parameter was used. */
439 /* The below is of course bogus */
440 if (foo_read(new_client,FOO_REG_GENERIC) != FOO_GENERIC_VALUE)
444 /* SENSORS ONLY START */
446 /* Next, specific detection. This is especially important for `sensors'
449 /* Determine the chip type. Not needed if a `force_CHIPTYPE' parameter
452 i = foo_read(new_client,FOO_REG_CHIPTYPE);
454 kind = chip1; /* As defined in the enum */
455 else if (i == FOO_TYPE_2)
458 printk("foo: Ignoring 'force' parameter for unknown chip at "
459 "adapter %d, address 0x%02x\n",i2c_adapter_id(adapter),address);
464 /* Now set the type and chip names */
466 type_name = "chip1"; /* For /proc entry */
467 client_name = "CHIP 1";
468 } else if (kind == chip2) {
469 type_name = "chip2"; /* For /proc entry */
470 client_name = "CHIP 2";
473 /* Reserve the ISA region */
475 request_region(address,FOO_EXTENT,type_name);
477 /* SENSORS ONLY END */
479 /* Fill in the remaining client fields. */
480 strcpy(new_client->name,client_name);
482 /* SENSORS ONLY BEGIN */
484 /* SENSORS ONLY END */
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 */
530 Removing the client (Legacy model)
531 ==================================
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)))
550 /* HYBRID SENSORS CHIP ONLY START */
551 if i2c_is_isa_client(client)
552 release_region(client->addr,LM78_EXTENT);
553 /* HYBRID SENSORS CHIP ONLY END */
555 kfree(i2c_get_clientdata(client));
560 Initializing the module or kernel
561 =================================
563 When the kernel is booted, or when your foo driver module is inserted,
564 you have to do some initializing. Fortunately, just attaching (registering)
565 the driver module is usually enough.
567 /* Keep track of how far we got in the initialization process. If several
568 things have to initialized, and we fail halfway, only those things
569 have to be cleaned up! */
570 static int __initdata foo_initialized = 0;
572 static int __init foo_init(void)
575 printk("foo version %s (%s)\n",FOO_VERSION,FOO_DATE);
577 if ((res = i2c_add_driver(&foo_driver))) {
578 printk("foo: Driver registration failed, module not inserted.\n");
586 void foo_cleanup(void)
588 if (foo_initialized == 1) {
589 i2c_del_driver(&foo_driver);
594 /* Substitute your own name and email address */
595 MODULE_AUTHOR("Frodo Looijaard <frodol@dds.nl>"
596 MODULE_DESCRIPTION("Driver for Barf Inc. Foo I2C devices");
598 module_init(foo_init);
599 module_exit(foo_cleanup);
601 Note that some functions are marked by `__init', and some data structures
602 by `__init_data'. Hose functions and structures can be removed after
603 kernel booting (or module loading) is completed.
609 If your I2C device needs special handling when entering a system low
610 power state -- like putting a transceiver into a low power mode, or
611 activating a system wakeup mechanism -- do that in the suspend() method.
612 The resume() method should reverse what the suspend() method does.
614 These are standard driver model calls, and they work just like they
615 would for any other driver stack. The calls can sleep, and can use
616 I2C messaging to the device being suspended or resumed (since their
617 parent I2C adapter is active when these calls are issued, and IRQs
624 If your I2C device needs special handling when the system shuts down
625 or reboots (including kexec) -- like turning something off -- use a
628 Again, this is a standard driver model call, working just like it
629 would for any other driver stack: the calls can sleep, and can use
636 A generic ioctl-like function call back is supported. You will seldom
637 need this, and its use is deprecated anyway, so newer design should not
638 use it. Set it to NULL.
641 Sending and receiving
642 =====================
644 If you want to communicate with your device, there are several functions
645 to do this. You can find all of them in i2c.h.
647 If you can choose between plain i2c communication and SMBus level
648 communication, please use the last. All adapters understand SMBus level
649 commands, but only some of them understand plain i2c!
652 Plain i2c communication
653 -----------------------
655 extern int i2c_master_send(struct i2c_client *,const char* ,int);
656 extern int i2c_master_recv(struct i2c_client *,char* ,int);
658 These routines read and write some bytes from/to a client. The client
659 contains the i2c address, so you do not have to include it. The second
660 parameter contains the bytes the read/write, the third the length of the
661 buffer. Returned is the actual number of bytes read/written.
663 extern int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msg,
666 This sends a series of messages. Each message can be a read or write,
667 and they can be mixed in any way. The transactions are combined: no
668 stop bit is sent between transaction. The i2c_msg structure contains
669 for each message the client address, the number of bytes of the message
670 and the message data itself.
672 You can read the file `i2c-protocol' for more information about the
679 extern s32 i2c_smbus_xfer (struct i2c_adapter * adapter, u16 addr,
680 unsigned short flags,
681 char read_write, u8 command, int size,
682 union i2c_smbus_data * data);
684 This is the generic SMBus function. All functions below are implemented
685 in terms of it. Never use this function directly!
688 extern s32 i2c_smbus_write_quick(struct i2c_client * client, u8 value);
689 extern s32 i2c_smbus_read_byte(struct i2c_client * client);
690 extern s32 i2c_smbus_write_byte(struct i2c_client * client, u8 value);
691 extern s32 i2c_smbus_read_byte_data(struct i2c_client * client, u8 command);
692 extern s32 i2c_smbus_write_byte_data(struct i2c_client * client,
693 u8 command, u8 value);
694 extern s32 i2c_smbus_read_word_data(struct i2c_client * client, u8 command);
695 extern s32 i2c_smbus_write_word_data(struct i2c_client * client,
696 u8 command, u16 value);
697 extern s32 i2c_smbus_write_block_data(struct i2c_client * client,
698 u8 command, u8 length,
700 extern s32 i2c_smbus_read_i2c_block_data(struct i2c_client * client,
701 u8 command, u8 *values);
703 These ones were removed in Linux 2.6.10 because they had no users, but could
704 be added back later if needed:
706 extern s32 i2c_smbus_read_block_data(struct i2c_client * client,
707 u8 command, u8 *values);
708 extern s32 i2c_smbus_write_i2c_block_data(struct i2c_client * client,
709 u8 command, u8 length,
711 extern s32 i2c_smbus_process_call(struct i2c_client * client,
712 u8 command, u16 value);
713 extern s32 i2c_smbus_block_process_call(struct i2c_client *client,
714 u8 command, u8 length,
717 All these transactions return -1 on failure. The 'write' transactions
718 return 0 on success; the 'read' transactions return the read value, except
719 for read_block, which returns the number of values read. The block buffers
720 need not be longer than 32 bytes.
722 You can read the file `smbus-protocol' for more information about the
723 actual SMBus protocol.
726 General purpose routines
727 ========================
729 Below all general purpose routines are listed, that were not mentioned
732 /* This call returns a unique low identifier for each registered adapter,
733 * or -1 if the adapter was not registered.
735 extern int i2c_adapter_id(struct i2c_adapter *adap);
738 The sensors sysctl/proc interface
739 =================================
741 This section only applies if you write `sensors' drivers.
743 Each sensors driver creates a directory in /proc/sys/dev/sensors for each
744 registered client. The directory is called something like foo-i2c-4-65.
745 The sensors module helps you to do this as easily as possible.
750 You will need to define a ctl_table template. This template will automatically
751 be copied to a newly allocated structure and filled in where necessary when
752 you call sensors_register_entry.
754 First, I will give an example definition.
755 static ctl_table foo_dir_table_template[] = {
756 { FOO_SYSCTL_FUNC1, "func1", NULL, 0, 0644, NULL, &i2c_proc_real,
757 &i2c_sysctl_real,NULL,&foo_func },
758 { FOO_SYSCTL_FUNC2, "func2", NULL, 0, 0644, NULL, &i2c_proc_real,
759 &i2c_sysctl_real,NULL,&foo_func },
760 { FOO_SYSCTL_DATA, "data", NULL, 0, 0644, NULL, &i2c_proc_real,
761 &i2c_sysctl_real,NULL,&foo_data },
765 In the above example, three entries are defined. They can either be
766 accessed through the /proc interface, in the /proc/sys/dev/sensors/*
767 directories, as files named func1, func2 and data, or alternatively
768 through the sysctl interface, in the appropriate table, with identifiers
769 FOO_SYSCTL_FUNC1, FOO_SYSCTL_FUNC2 and FOO_SYSCTL_DATA.
771 The third, sixth and ninth parameters should always be NULL, and the
772 fourth should always be 0. The fifth is the mode of the /proc file;
773 0644 is safe, as the file will be owned by root:root.
775 The seventh and eighth parameters should be &i2c_proc_real and
776 &i2c_sysctl_real if you want to export lists of reals (scaled
777 integers). You can also use your own function for them, as usual.
778 Finally, the last parameter is the call-back to gather the data
779 (see below) if you use the *_proc_real functions.
785 The call back functions (foo_func and foo_data in the above example)
786 can be called in several ways; the operation parameter determines
789 * If operation == SENSORS_PROC_REAL_INFO, you must return the
790 magnitude (scaling) in nrels_mag;
791 * If operation == SENSORS_PROC_REAL_READ, you must read information
792 from the chip and return it in results. The number of integers
793 to display should be put in nrels_mag;
794 * If operation == SENSORS_PROC_REAL_WRITE, you must write the
795 supplied information to the chip. nrels_mag will contain the number
796 of integers, results the integers themselves.
798 The *_proc_real functions will display the elements as reals for the
799 /proc interface. If you set the magnitude to 2, and supply 345 for
800 SENSORS_PROC_REAL_READ, it would display 3.45; and if the user would
801 write 45.6 to the /proc file, it would be returned as 4560 for
802 SENSORS_PROC_REAL_WRITE. A magnitude may even be negative!
806 /* FOO_FROM_REG and FOO_TO_REG translate between scaled values and
807 register values. Note the use of the read cache. */
808 void foo_in(struct i2c_client *client, int operation, int ctl_name,
809 int *nrels_mag, long *results)
811 struct foo_data *data = client->data;
812 int nr = ctl_name - FOO_SYSCTL_FUNC1; /* reduce to 0 upwards */
814 if (operation == SENSORS_PROC_REAL_INFO)
816 else if (operation == SENSORS_PROC_REAL_READ) {
817 /* Update the readings cache (if necessary) */
818 foo_update_client(client);
819 /* Get the readings from the cache */
820 results[0] = FOO_FROM_REG(data->foo_func_base[nr]);
821 results[1] = FOO_FROM_REG(data->foo_func_more[nr]);
822 results[2] = FOO_FROM_REG(data->foo_func_readonly[nr]);
824 } else if (operation == SENSORS_PROC_REAL_WRITE) {
825 if (*nrels_mag >= 1) {
826 /* Update the cache */
827 data->foo_base[nr] = FOO_TO_REG(results[0]);
828 /* Update the chip */
829 foo_write_value(client,FOO_REG_FUNC_BASE(nr),data->foo_base[nr]);
831 if (*nrels_mag >= 2) {
832 /* Update the cache */
833 data->foo_more[nr] = FOO_TO_REG(results[1]);
834 /* Update the chip */
835 foo_write_value(client,FOO_REG_FUNC_MORE(nr),data->foo_more[nr]);