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Linus Torvalds1da177e2005-04-16 15:20:36 -07001This is a small guide for those who want to write kernel drivers for I2C
David Brownell4298cfc2007-05-01 23:26:31 +02002or SMBus devices, using Linux as the protocol host/master (not slave).
Linus Torvalds1da177e2005-04-16 15:20:36 -07003
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
David Brownellf37dd802007-02-13 22:09:00 +010024routines, and should be zero-initialized except for fields with data you
25provide. A client structure holds device-specific information like the
26driver model device node, and its I2C address.
Linus Torvalds1da177e2005-04-16 15:20:36 -070027
28static struct i2c_driver foo_driver = {
Jean Delvared45d2042005-11-26 20:55:35 +010029 .driver = {
Jean Delvared45d2042005-11-26 20:55:35 +010030 .name = "foo",
31 },
David Brownell4298cfc2007-05-01 23:26:31 +020032
33 /* iff driver uses driver model ("new style") binding model: */
34 .probe = foo_probe,
35 .remove = foo_remove,
36
37 /* else, driver uses "legacy" binding model: */
David Brownellf37dd802007-02-13 22:09:00 +010038 .attach_adapter = foo_attach_adapter,
39 .detach_client = foo_detach_client,
David Brownell4298cfc2007-05-01 23:26:31 +020040
41 /* these may be used regardless of the driver binding model */
David Brownellf37dd802007-02-13 22:09:00 +010042 .shutdown = foo_shutdown, /* optional */
43 .suspend = foo_suspend, /* optional */
44 .resume = foo_resume, /* optional */
45 .command = foo_command, /* optional */
Linus Torvalds1da177e2005-04-16 15:20:36 -070046}
47
David Brownellf37dd802007-02-13 22:09:00 +010048The name field is the driver name, and must not contain spaces. It
49should match the module name (if the driver can be compiled as a module),
50although you can use MODULE_ALIAS (passing "foo" in this example) to add
David Brownell4298cfc2007-05-01 23:26:31 +020051another name for the module. If the driver name doesn't match the module
52name, the module won't be automatically loaded (hotplug/coldplug).
Linus Torvalds1da177e2005-04-16 15:20:36 -070053
Linus Torvalds1da177e2005-04-16 15:20:36 -070054All other fields are for call-back functions which will be explained
55below.
56
Linus Torvalds1da177e2005-04-16 15:20:36 -070057
58Extra client data
59=================
60
David Brownellf37dd802007-02-13 22:09:00 +010061Each client structure has a special `data' field that can point to any
62structure at all. You should use this to keep device-specific data,
63especially in drivers that handle multiple I2C or SMBUS devices. You
Linus Torvalds1da177e2005-04-16 15:20:36 -070064do not always need this, but especially for `sensors' drivers, it can
65be very useful.
66
David Brownellf37dd802007-02-13 22:09:00 +010067 /* store the value */
68 void i2c_set_clientdata(struct i2c_client *client, void *data);
69
70 /* retrieve the value */
71 void *i2c_get_clientdata(struct i2c_client *client);
72
Linus Torvalds1da177e2005-04-16 15:20:36 -070073An example structure is below.
74
75 struct foo_data {
Jean Delvare2445eb62005-10-17 23:16:25 +020076 struct i2c_client client;
Linus Torvalds1da177e2005-04-16 15:20:36 -070077 enum chips type; /* To keep the chips type for `sensors' drivers. */
78
79 /* Because the i2c bus is slow, it is often useful to cache the read
80 information of a chip for some time (for example, 1 or 2 seconds).
81 It depends of course on the device whether this is really worthwhile
82 or even sensible. */
Jean Delvareeefcd752007-05-01 23:26:35 +020083 struct mutex update_lock; /* When we are reading lots of information,
Linus Torvalds1da177e2005-04-16 15:20:36 -070084 another process should not update the
85 below information */
86 char valid; /* != 0 if the following fields are valid. */
87 unsigned long last_updated; /* In jiffies */
88 /* Add the read information here too */
89 };
90
91
92Accessing the client
93====================
94
95Let's say we have a valid client structure. At some time, we will need
96to gather information from the client, or write new information to the
97client. How we will export this information to user-space is less
98important at this moment (perhaps we do not need to do this at all for
99some obscure clients). But we need generic reading and writing routines.
100
101I have found it useful to define foo_read and foo_write function for this.
102For some cases, it will be easier to call the i2c functions directly,
103but many chips have some kind of register-value idea that can easily
Jean Delvareeefcd752007-05-01 23:26:35 +0200104be encapsulated.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700105
106The below functions are simple examples, and should not be copied
107literally.
108
109 int foo_read_value(struct i2c_client *client, u8 reg)
110 {
111 if (reg < 0x10) /* byte-sized register */
112 return i2c_smbus_read_byte_data(client,reg);
113 else /* word-sized register */
114 return i2c_smbus_read_word_data(client,reg);
115 }
116
117 int foo_write_value(struct i2c_client *client, u8 reg, u16 value)
118 {
119 if (reg == 0x10) /* Impossible to write - driver error! */ {
120 return -1;
121 else if (reg < 0x10) /* byte-sized register */
122 return i2c_smbus_write_byte_data(client,reg,value);
123 else /* word-sized register */
124 return i2c_smbus_write_word_data(client,reg,value);
125 }
126
Linus Torvalds1da177e2005-04-16 15:20:36 -0700127
128Probing and attaching
129=====================
130
David Brownell4298cfc2007-05-01 23:26:31 +0200131The Linux I2C stack was originally written to support access to hardware
132monitoring chips on PC motherboards, and thus it embeds some assumptions
133that are more appropriate to SMBus (and PCs) than to I2C. One of these
134assumptions is that most adapters and devices drivers support the SMBUS_QUICK
135protocol to probe device presence. Another is that devices and their drivers
136can be sufficiently configured using only such probe primitives.
137
138As Linux and its I2C stack became more widely used in embedded systems
139and complex components such as DVB adapters, those assumptions became more
140problematic. Drivers for I2C devices that issue interrupts need more (and
141different) configuration information, as do drivers handling chip variants
142that can't be distinguished by protocol probing, or which need some board
143specific information to operate correctly.
144
145Accordingly, the I2C stack now has two models for associating I2C devices
146with their drivers: the original "legacy" model, and a newer one that's
147fully compatible with the Linux 2.6 driver model. These models do not mix,
148since the "legacy" model requires drivers to create "i2c_client" device
149objects after SMBus style probing, while the Linux driver model expects
150drivers to be given such device objects in their probe() routines.
151
152
153Standard Driver Model Binding ("New Style")
154-------------------------------------------
155
156System infrastructure, typically board-specific initialization code or
157boot firmware, reports what I2C devices exist. For example, there may be
158a table, in the kernel or from the boot loader, identifying I2C devices
159and linking them to board-specific configuration information about IRQs
160and other wiring artifacts, chip type, and so on. That could be used to
161create i2c_client objects for each I2C device.
162
163I2C device drivers using this binding model work just like any other
164kind of driver in Linux: they provide a probe() method to bind to
165those devices, and a remove() method to unbind.
166
167 static int foo_probe(struct i2c_client *client);
168 static int foo_remove(struct i2c_client *client);
169
170Remember that the i2c_driver does not create those client handles. The
171handle may be used during foo_probe(). If foo_probe() reports success
172(zero not a negative status code) it may save the handle and use it until
173foo_remove() returns. That binding model is used by most Linux drivers.
174
175Drivers match devices when i2c_client.driver_name and the driver name are
176the same; this approach is used in several other busses that don't have
177device typing support in the hardware. The driver and module name should
178match, so hotplug/coldplug mechanisms will modprobe the driver.
179
180
Jean Delvarece9e0792007-05-01 23:26:32 +0200181Device Creation (Standard driver model)
182---------------------------------------
183
184If you know for a fact that an I2C device is connected to a given I2C bus,
185you can instantiate that device by simply filling an i2c_board_info
186structure with the device address and driver name, and calling
187i2c_new_device(). This will create the device, then the driver core will
188take care of finding the right driver and will call its probe() method.
189If a driver supports different device types, you can specify the type you
190want using the type field. You can also specify an IRQ and platform data
191if needed.
192
193Sometimes you know that a device is connected to a given I2C bus, but you
194don't know the exact address it uses. This happens on TV adapters for
195example, where the same driver supports dozens of slightly different
196models, and I2C device addresses change from one model to the next. In
197that case, you can use the i2c_new_probed_device() variant, which is
198similar to i2c_new_device(), except that it takes an additional list of
199possible I2C addresses to probe. A device is created for the first
200responsive address in the list. If you expect more than one device to be
201present in the address range, simply call i2c_new_probed_device() that
202many times.
203
204The call to i2c_new_device() or i2c_new_probed_device() typically happens
205in the I2C bus driver. You may want to save the returned i2c_client
206reference for later use.
207
208
209Device Deletion (Standard driver model)
210---------------------------------------
211
212Each I2C device which has been created using i2c_new_device() or
213i2c_new_probed_device() can be unregistered by calling
214i2c_unregister_device(). If you don't call it explicitly, it will be
215called automatically before the underlying I2C bus itself is removed, as a
216device can't survive its parent in the device driver model.
217
218
David Brownell4298cfc2007-05-01 23:26:31 +0200219Legacy Driver Binding Model
220---------------------------
221
Linus Torvalds1da177e2005-04-16 15:20:36 -0700222Most i2c devices can be present on several i2c addresses; for some this
223is determined in hardware (by soldering some chip pins to Vcc or Ground),
224for others this can be changed in software (by writing to specific client
225registers). Some devices are usually on a specific address, but not always;
226and some are even more tricky. So you will probably need to scan several
227i2c addresses for your clients, and do some sort of detection to see
228whether it is actually a device supported by your driver.
229
230To give the user a maximum of possibilities, some default module parameters
231are defined to help determine what addresses are scanned. Several macros
232are defined in i2c.h to help you support them, as well as a generic
233detection algorithm.
234
235You do not have to use this parameter interface; but don't try to use
Jean Delvare2ed2dc32005-07-31 21:42:02 +0200236function i2c_probe() if you don't.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700237
Linus Torvalds1da177e2005-04-16 15:20:36 -0700238
David Brownell4298cfc2007-05-01 23:26:31 +0200239Probing classes (Legacy model)
240------------------------------
Linus Torvalds1da177e2005-04-16 15:20:36 -0700241
242All parameters are given as lists of unsigned 16-bit integers. Lists are
243terminated by I2C_CLIENT_END.
244The following lists are used internally:
245
246 normal_i2c: filled in by the module writer.
247 A list of I2C addresses which should normally be examined.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700248 probe: insmod parameter.
249 A list of pairs. The first value is a bus number (-1 for any I2C bus),
250 the second is the address. These addresses are also probed, as if they
251 were in the 'normal' list.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700252 ignore: insmod parameter.
253 A list of pairs. The first value is a bus number (-1 for any I2C bus),
254 the second is the I2C address. These addresses are never probed.
Jean Delvaref4b50262005-07-31 21:49:03 +0200255 This parameter overrules the 'normal_i2c' list only.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700256 force: insmod parameter.
257 A list of pairs. The first value is a bus number (-1 for any I2C bus),
258 the second is the I2C address. A device is blindly assumed to be on
259 the given address, no probing is done.
260
Jean Delvaref4b50262005-07-31 21:49:03 +0200261Additionally, kind-specific force lists may optionally be defined if
262the driver supports several chip kinds. They are grouped in a
263NULL-terminated list of pointers named forces, those first element if the
264generic force list mentioned above. Each additional list correspond to an
265insmod parameter of the form force_<kind>.
266
Jean Delvareb3d5496e2005-04-02 20:31:02 +0200267Fortunately, as a module writer, you just have to define the `normal_i2c'
268parameter. The complete declaration could look like this:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700269
Jean Delvare2cdddeb2008-01-27 18:14:47 +0100270 /* Scan 0x4c to 0x4f */
271 static const unsigned short normal_i2c[] = { 0x4c, 0x4d, 0x4e, 0x4f,
272 I2C_CLIENT_END };
Linus Torvalds1da177e2005-04-16 15:20:36 -0700273
274 /* Magic definition of all other variables and things */
275 I2C_CLIENT_INSMOD;
Jean Delvaref4b50262005-07-31 21:49:03 +0200276 /* Or, if your driver supports, say, 2 kind of devices: */
277 I2C_CLIENT_INSMOD_2(foo, bar);
278
279If you use the multi-kind form, an enum will be defined for you:
280 enum chips { any_chip, foo, bar, ... }
281You can then (and certainly should) use it in the driver code.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700282
Jean Delvareb3d5496e2005-04-02 20:31:02 +0200283Note that you *have* to call the defined variable `normal_i2c',
284without any prefix!
Linus Torvalds1da177e2005-04-16 15:20:36 -0700285
286
David Brownell4298cfc2007-05-01 23:26:31 +0200287Attaching to an adapter (Legacy model)
288--------------------------------------
Linus Torvalds1da177e2005-04-16 15:20:36 -0700289
290Whenever a new adapter is inserted, or for all adapters if the driver is
291being registered, the callback attach_adapter() is called. Now is the
292time to determine what devices are present on the adapter, and to register
293a client for each of them.
294
295The attach_adapter callback is really easy: we just call the generic
296detection function. This function will scan the bus for us, using the
297information as defined in the lists explained above. If a device is
298detected at a specific address, another callback is called.
299
300 int foo_attach_adapter(struct i2c_adapter *adapter)
301 {
302 return i2c_probe(adapter,&addr_data,&foo_detect_client);
303 }
304
Linus Torvalds1da177e2005-04-16 15:20:36 -0700305Remember, structure `addr_data' is defined by the macros explained above,
306so you do not have to define it yourself.
307
Jean Delvare2ed2dc32005-07-31 21:42:02 +0200308The i2c_probe function will call the foo_detect_client
Linus Torvalds1da177e2005-04-16 15:20:36 -0700309function only for those i2c addresses that actually have a device on
310them (unless a `force' parameter was used). In addition, addresses that
311are already in use (by some other registered client) are skipped.
312
313
David Brownell4298cfc2007-05-01 23:26:31 +0200314The detect client function (Legacy model)
315-----------------------------------------
Linus Torvalds1da177e2005-04-16 15:20:36 -0700316
Jean Delvare2ed2dc32005-07-31 21:42:02 +0200317The detect client function is called by i2c_probe. The `kind' parameter
318contains -1 for a probed detection, 0 for a forced detection, or a positive
319number for a forced detection with a chip type forced.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700320
Jean Delvarea89ba0b2005-08-09 20:17:55 +0200321Returning an error different from -ENODEV in a detect function will cause
322the detection to stop: other addresses and adapters won't be scanned.
323This should only be done on fatal or internal errors, such as a memory
324shortage or i2c_attach_client failing.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700325
326For now, you can ignore the `flags' parameter. It is there for future use.
327
328 int foo_detect_client(struct i2c_adapter *adapter, int address,
Jean Delvareeefcd752007-05-01 23:26:35 +0200329 int kind)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700330 {
331 int err = 0;
332 int i;
Jean Delvareeefcd752007-05-01 23:26:35 +0200333 struct i2c_client *client;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700334 struct foo_data *data;
Jean Delvareeefcd752007-05-01 23:26:35 +0200335 const char *name = "";
Linus Torvalds1da177e2005-04-16 15:20:36 -0700336
337 /* Let's see whether this adapter can support what we need.
Jean Delvareeefcd752007-05-01 23:26:35 +0200338 Please substitute the things you need here! */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700339 if (!i2c_check_functionality(adapter,I2C_FUNC_SMBUS_WORD_DATA |
340 I2C_FUNC_SMBUS_WRITE_BYTE))
341 goto ERROR0;
342
Linus Torvalds1da177e2005-04-16 15:20:36 -0700343 /* OK. For now, we presume we have a valid client. We now create the
344 client structure, even though we cannot fill it completely yet.
345 But it allows us to access several i2c functions safely */
346
Jean Delvare2445eb62005-10-17 23:16:25 +0200347 if (!(data = kzalloc(sizeof(struct foo_data), GFP_KERNEL))) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700348 err = -ENOMEM;
349 goto ERROR0;
350 }
351
Jean Delvareeefcd752007-05-01 23:26:35 +0200352 client = &data->client;
353 i2c_set_clientdata(client, data);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700354
Jean Delvareeefcd752007-05-01 23:26:35 +0200355 client->addr = address;
356 client->adapter = adapter;
357 client->driver = &foo_driver;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700358
359 /* Now, we do the remaining detection. If no `force' parameter is used. */
360
361 /* First, the generic detection (if any), that is skipped if any force
362 parameter was used. */
363 if (kind < 0) {
364 /* The below is of course bogus */
Jean Delvareeefcd752007-05-01 23:26:35 +0200365 if (foo_read(client, FOO_REG_GENERIC) != FOO_GENERIC_VALUE)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700366 goto ERROR1;
367 }
368
Linus Torvalds1da177e2005-04-16 15:20:36 -0700369 /* Next, specific detection. This is especially important for `sensors'
370 devices. */
371
372 /* Determine the chip type. Not needed if a `force_CHIPTYPE' parameter
373 was used. */
374 if (kind <= 0) {
Jean Delvareeefcd752007-05-01 23:26:35 +0200375 i = foo_read(client, FOO_REG_CHIPTYPE);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700376 if (i == FOO_TYPE_1)
377 kind = chip1; /* As defined in the enum */
378 else if (i == FOO_TYPE_2)
379 kind = chip2;
380 else {
381 printk("foo: Ignoring 'force' parameter for unknown chip at "
382 "adapter %d, address 0x%02x\n",i2c_adapter_id(adapter),address);
383 goto ERROR1;
384 }
385 }
386
387 /* Now set the type and chip names */
388 if (kind == chip1) {
Jean Delvareeefcd752007-05-01 23:26:35 +0200389 name = "chip1";
Linus Torvalds1da177e2005-04-16 15:20:36 -0700390 } else if (kind == chip2) {
Jean Delvareeefcd752007-05-01 23:26:35 +0200391 name = "chip2";
Linus Torvalds1da177e2005-04-16 15:20:36 -0700392 }
393
Linus Torvalds1da177e2005-04-16 15:20:36 -0700394 /* Fill in the remaining client fields. */
Jean Delvareeefcd752007-05-01 23:26:35 +0200395 strlcpy(client->name, name, I2C_NAME_SIZE);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700396 data->type = kind;
Jean Delvareeefcd752007-05-01 23:26:35 +0200397 mutex_init(&data->update_lock); /* Only if you use this field */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700398
399 /* Any other initializations in data must be done here too. */
400
Linus Torvalds1da177e2005-04-16 15:20:36 -0700401 /* This function can write default values to the client registers, if
402 needed. */
Jean Delvareeefcd752007-05-01 23:26:35 +0200403 foo_init_client(client);
404
405 /* Tell the i2c layer a new client has arrived */
406 if ((err = i2c_attach_client(client)))
407 goto ERROR1;
408
Linus Torvalds1da177e2005-04-16 15:20:36 -0700409 return 0;
410
411 /* OK, this is not exactly good programming practice, usually. But it is
412 very code-efficient in this case. */
413
Linus Torvalds1da177e2005-04-16 15:20:36 -0700414 ERROR1:
Jean Delvarea852daa2005-11-02 21:42:48 +0100415 kfree(data);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700416 ERROR0:
417 return err;
418 }
419
420
David Brownell4298cfc2007-05-01 23:26:31 +0200421Removing the client (Legacy model)
422==================================
Linus Torvalds1da177e2005-04-16 15:20:36 -0700423
424The detach_client call back function is called when a client should be
425removed. It may actually fail, but only when panicking. This code is
426much simpler than the attachment code, fortunately!
427
428 int foo_detach_client(struct i2c_client *client)
429 {
Jean Delvareeefcd752007-05-01 23:26:35 +0200430 int err;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700431
432 /* Try to detach the client from i2c space */
Jean Delvare7bef5592005-07-27 22:14:49 +0200433 if ((err = i2c_detach_client(client)))
Linus Torvalds1da177e2005-04-16 15:20:36 -0700434 return err;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700435
Jean Delvarea852daa2005-11-02 21:42:48 +0100436 kfree(i2c_get_clientdata(client));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700437 return 0;
438 }
439
440
441Initializing the module or kernel
442=================================
443
444When the kernel is booted, or when your foo driver module is inserted,
445you have to do some initializing. Fortunately, just attaching (registering)
446the driver module is usually enough.
447
Linus Torvalds1da177e2005-04-16 15:20:36 -0700448 static int __init foo_init(void)
449 {
450 int res;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700451
452 if ((res = i2c_add_driver(&foo_driver))) {
453 printk("foo: Driver registration failed, module not inserted.\n");
Linus Torvalds1da177e2005-04-16 15:20:36 -0700454 return res;
455 }
Linus Torvalds1da177e2005-04-16 15:20:36 -0700456 return 0;
457 }
458
Jean Delvareeefcd752007-05-01 23:26:35 +0200459 static void __exit foo_cleanup(void)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700460 {
Jean Delvareeefcd752007-05-01 23:26:35 +0200461 i2c_del_driver(&foo_driver);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700462 }
463
464 /* Substitute your own name and email address */
465 MODULE_AUTHOR("Frodo Looijaard <frodol@dds.nl>"
466 MODULE_DESCRIPTION("Driver for Barf Inc. Foo I2C devices");
467
Jean Delvareeefcd752007-05-01 23:26:35 +0200468 /* a few non-GPL license types are also allowed */
469 MODULE_LICENSE("GPL");
470
Linus Torvalds1da177e2005-04-16 15:20:36 -0700471 module_init(foo_init);
472 module_exit(foo_cleanup);
473
474Note that some functions are marked by `__init', and some data structures
Jean Delvareeefcd752007-05-01 23:26:35 +0200475by `__initdata'. These functions and structures can be removed after
Linus Torvalds1da177e2005-04-16 15:20:36 -0700476kernel booting (or module loading) is completed.
477
Jean Delvarefb687d72005-12-18 16:51:55 +0100478
David Brownellf37dd802007-02-13 22:09:00 +0100479Power Management
480================
481
482If your I2C device needs special handling when entering a system low
483power state -- like putting a transceiver into a low power mode, or
484activating a system wakeup mechanism -- do that in the suspend() method.
485The resume() method should reverse what the suspend() method does.
486
487These are standard driver model calls, and they work just like they
488would for any other driver stack. The calls can sleep, and can use
489I2C messaging to the device being suspended or resumed (since their
490parent I2C adapter is active when these calls are issued, and IRQs
491are still enabled).
492
493
494System Shutdown
495===============
496
497If your I2C device needs special handling when the system shuts down
498or reboots (including kexec) -- like turning something off -- use a
499shutdown() method.
500
501Again, this is a standard driver model call, working just like it
502would for any other driver stack: the calls can sleep, and can use
503I2C messaging.
504
505
Linus Torvalds1da177e2005-04-16 15:20:36 -0700506Command function
507================
508
509A generic ioctl-like function call back is supported. You will seldom
Jean Delvarefb687d72005-12-18 16:51:55 +0100510need this, and its use is deprecated anyway, so newer design should not
511use it. Set it to NULL.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700512
513
514Sending and receiving
515=====================
516
517If you want to communicate with your device, there are several functions
518to do this. You can find all of them in i2c.h.
519
520If you can choose between plain i2c communication and SMBus level
521communication, please use the last. All adapters understand SMBus level
522commands, but only some of them understand plain i2c!
523
524
525Plain i2c communication
526-----------------------
527
528 extern int i2c_master_send(struct i2c_client *,const char* ,int);
529 extern int i2c_master_recv(struct i2c_client *,char* ,int);
530
531These routines read and write some bytes from/to a client. The client
532contains the i2c address, so you do not have to include it. The second
533parameter contains the bytes the read/write, the third the length of the
534buffer. Returned is the actual number of bytes read/written.
535
536 extern int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msg,
537 int num);
538
539This sends a series of messages. Each message can be a read or write,
540and they can be mixed in any way. The transactions are combined: no
541stop bit is sent between transaction. The i2c_msg structure contains
542for each message the client address, the number of bytes of the message
543and the message data itself.
544
545You can read the file `i2c-protocol' for more information about the
546actual i2c protocol.
547
548
549SMBus communication
550-------------------
551
552 extern s32 i2c_smbus_xfer (struct i2c_adapter * adapter, u16 addr,
553 unsigned short flags,
554 char read_write, u8 command, int size,
555 union i2c_smbus_data * data);
556
557 This is the generic SMBus function. All functions below are implemented
558 in terms of it. Never use this function directly!
559
560
561 extern s32 i2c_smbus_write_quick(struct i2c_client * client, u8 value);
562 extern s32 i2c_smbus_read_byte(struct i2c_client * client);
563 extern s32 i2c_smbus_write_byte(struct i2c_client * client, u8 value);
564 extern s32 i2c_smbus_read_byte_data(struct i2c_client * client, u8 command);
565 extern s32 i2c_smbus_write_byte_data(struct i2c_client * client,
566 u8 command, u8 value);
567 extern s32 i2c_smbus_read_word_data(struct i2c_client * client, u8 command);
568 extern s32 i2c_smbus_write_word_data(struct i2c_client * client,
569 u8 command, u16 value);
570 extern s32 i2c_smbus_write_block_data(struct i2c_client * client,
571 u8 command, u8 length,
572 u8 *values);
Jean Delvare7865e242005-10-08 00:00:31 +0200573 extern s32 i2c_smbus_read_i2c_block_data(struct i2c_client * client,
Jean Delvare4b2643d2007-07-12 14:12:29 +0200574 u8 command, u8 length, u8 *values);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700575
576These ones were removed in Linux 2.6.10 because they had no users, but could
577be added back later if needed:
578
Linus Torvalds1da177e2005-04-16 15:20:36 -0700579 extern s32 i2c_smbus_read_block_data(struct i2c_client * client,
580 u8 command, u8 *values);
581 extern s32 i2c_smbus_write_i2c_block_data(struct i2c_client * client,
582 u8 command, u8 length,
583 u8 *values);
584 extern s32 i2c_smbus_process_call(struct i2c_client * client,
585 u8 command, u16 value);
586 extern s32 i2c_smbus_block_process_call(struct i2c_client *client,
587 u8 command, u8 length,
588 u8 *values)
589
590All these transactions return -1 on failure. The 'write' transactions
591return 0 on success; the 'read' transactions return the read value, except
592for read_block, which returns the number of values read. The block buffers
593need not be longer than 32 bytes.
594
595You can read the file `smbus-protocol' for more information about the
596actual SMBus protocol.
597
598
599General purpose routines
600========================
601
602Below all general purpose routines are listed, that were not mentioned
603before.
604
Jean Delvareeefcd752007-05-01 23:26:35 +0200605 /* This call returns a unique low identifier for each registered adapter.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700606 */
607 extern int i2c_adapter_id(struct i2c_adapter *adap);
608