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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
Ben Dooks2260e632008-07-01 22:38:18 +020028/* iff driver uses driver model ("new style") binding model: */
29
30static struct i2c_device_id foo_idtable[] = {
31 { "foo", my_id_for_foo },
32 { "bar", my_id_for_bar },
33 { }
34};
35
36MODULE_DEVICE_TABLE(i2c, foo_idtable);
37
Linus Torvalds1da177e2005-04-16 15:20:36 -070038static struct i2c_driver foo_driver = {
Jean Delvared45d2042005-11-26 20:55:35 +010039 .driver = {
Jean Delvared45d2042005-11-26 20:55:35 +010040 .name = "foo",
41 },
David Brownell4298cfc2007-05-01 23:26:31 +020042
43 /* iff driver uses driver model ("new style") binding model: */
Ben Dooks2260e632008-07-01 22:38:18 +020044 .id_table = foo_ids,
David Brownell4298cfc2007-05-01 23:26:31 +020045 .probe = foo_probe,
46 .remove = foo_remove,
47
48 /* else, driver uses "legacy" binding model: */
David Brownellf37dd802007-02-13 22:09:00 +010049 .attach_adapter = foo_attach_adapter,
50 .detach_client = foo_detach_client,
David Brownell4298cfc2007-05-01 23:26:31 +020051
52 /* these may be used regardless of the driver binding model */
David Brownellf37dd802007-02-13 22:09:00 +010053 .shutdown = foo_shutdown, /* optional */
54 .suspend = foo_suspend, /* optional */
55 .resume = foo_resume, /* optional */
56 .command = foo_command, /* optional */
Linus Torvalds1da177e2005-04-16 15:20:36 -070057}
58
David Brownellf37dd802007-02-13 22:09:00 +010059The name field is the driver name, and must not contain spaces. It
60should match the module name (if the driver can be compiled as a module),
61although you can use MODULE_ALIAS (passing "foo" in this example) to add
David Brownell4298cfc2007-05-01 23:26:31 +020062another name for the module. If the driver name doesn't match the module
63name, the module won't be automatically loaded (hotplug/coldplug).
Linus Torvalds1da177e2005-04-16 15:20:36 -070064
Linus Torvalds1da177e2005-04-16 15:20:36 -070065All other fields are for call-back functions which will be explained
66below.
67
Linus Torvalds1da177e2005-04-16 15:20:36 -070068
69Extra client data
70=================
71
David Brownellf37dd802007-02-13 22:09:00 +010072Each client structure has a special `data' field that can point to any
73structure at all. You should use this to keep device-specific data,
74especially in drivers that handle multiple I2C or SMBUS devices. You
Linus Torvalds1da177e2005-04-16 15:20:36 -070075do not always need this, but especially for `sensors' drivers, it can
76be very useful.
77
David Brownellf37dd802007-02-13 22:09:00 +010078 /* store the value */
79 void i2c_set_clientdata(struct i2c_client *client, void *data);
80
81 /* retrieve the value */
82 void *i2c_get_clientdata(struct i2c_client *client);
83
Linus Torvalds1da177e2005-04-16 15:20:36 -070084An example structure is below.
85
86 struct foo_data {
Jean Delvare2445eb62005-10-17 23:16:25 +020087 struct i2c_client client;
Linus Torvalds1da177e2005-04-16 15:20:36 -070088 enum chips type; /* To keep the chips type for `sensors' drivers. */
89
90 /* Because the i2c bus is slow, it is often useful to cache the read
91 information of a chip for some time (for example, 1 or 2 seconds).
92 It depends of course on the device whether this is really worthwhile
93 or even sensible. */
Jean Delvareeefcd752007-05-01 23:26:35 +020094 struct mutex update_lock; /* When we are reading lots of information,
Linus Torvalds1da177e2005-04-16 15:20:36 -070095 another process should not update the
96 below information */
97 char valid; /* != 0 if the following fields are valid. */
98 unsigned long last_updated; /* In jiffies */
99 /* Add the read information here too */
100 };
101
102
103Accessing the client
104====================
105
106Let's say we have a valid client structure. At some time, we will need
107to gather information from the client, or write new information to the
108client. How we will export this information to user-space is less
109important at this moment (perhaps we do not need to do this at all for
110some obscure clients). But we need generic reading and writing routines.
111
112I have found it useful to define foo_read and foo_write function for this.
113For some cases, it will be easier to call the i2c functions directly,
114but many chips have some kind of register-value idea that can easily
Jean Delvareeefcd752007-05-01 23:26:35 +0200115be encapsulated.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700116
117The below functions are simple examples, and should not be copied
118literally.
119
120 int foo_read_value(struct i2c_client *client, u8 reg)
121 {
122 if (reg < 0x10) /* byte-sized register */
123 return i2c_smbus_read_byte_data(client,reg);
124 else /* word-sized register */
125 return i2c_smbus_read_word_data(client,reg);
126 }
127
128 int foo_write_value(struct i2c_client *client, u8 reg, u16 value)
129 {
130 if (reg == 0x10) /* Impossible to write - driver error! */ {
131 return -1;
132 else if (reg < 0x10) /* byte-sized register */
133 return i2c_smbus_write_byte_data(client,reg,value);
134 else /* word-sized register */
135 return i2c_smbus_write_word_data(client,reg,value);
136 }
137
Linus Torvalds1da177e2005-04-16 15:20:36 -0700138
139Probing and attaching
140=====================
141
David Brownell4298cfc2007-05-01 23:26:31 +0200142The Linux I2C stack was originally written to support access to hardware
143monitoring chips on PC motherboards, and thus it embeds some assumptions
144that are more appropriate to SMBus (and PCs) than to I2C. One of these
145assumptions is that most adapters and devices drivers support the SMBUS_QUICK
146protocol to probe device presence. Another is that devices and their drivers
147can be sufficiently configured using only such probe primitives.
148
149As Linux and its I2C stack became more widely used in embedded systems
150and complex components such as DVB adapters, those assumptions became more
151problematic. Drivers for I2C devices that issue interrupts need more (and
152different) configuration information, as do drivers handling chip variants
153that can't be distinguished by protocol probing, or which need some board
154specific information to operate correctly.
155
156Accordingly, the I2C stack now has two models for associating I2C devices
157with their drivers: the original "legacy" model, and a newer one that's
158fully compatible with the Linux 2.6 driver model. These models do not mix,
159since the "legacy" model requires drivers to create "i2c_client" device
160objects after SMBus style probing, while the Linux driver model expects
161drivers to be given such device objects in their probe() routines.
162
163
164Standard Driver Model Binding ("New Style")
165-------------------------------------------
166
167System infrastructure, typically board-specific initialization code or
168boot firmware, reports what I2C devices exist. For example, there may be
169a table, in the kernel or from the boot loader, identifying I2C devices
170and linking them to board-specific configuration information about IRQs
171and other wiring artifacts, chip type, and so on. That could be used to
172create i2c_client objects for each I2C device.
173
174I2C device drivers using this binding model work just like any other
175kind of driver in Linux: they provide a probe() method to bind to
176those devices, and a remove() method to unbind.
177
Jean Delvared2653e92008-04-29 23:11:39 +0200178 static int foo_probe(struct i2c_client *client,
179 const struct i2c_device_id *id);
David Brownell4298cfc2007-05-01 23:26:31 +0200180 static int foo_remove(struct i2c_client *client);
181
182Remember that the i2c_driver does not create those client handles. The
183handle may be used during foo_probe(). If foo_probe() reports success
184(zero not a negative status code) it may save the handle and use it until
185foo_remove() returns. That binding model is used by most Linux drivers.
186
Ben Dooks2260e632008-07-01 22:38:18 +0200187The probe function is called when an entry in the id_table name field
188matches the device's name. It is passed the entry that was matched so
189the driver knows which one in the table matched.
David Brownell4298cfc2007-05-01 23:26:31 +0200190
191
Jean Delvarece9e0792007-05-01 23:26:32 +0200192Device Creation (Standard driver model)
193---------------------------------------
194
195If you know for a fact that an I2C device is connected to a given I2C bus,
196you can instantiate that device by simply filling an i2c_board_info
197structure with the device address and driver name, and calling
198i2c_new_device(). This will create the device, then the driver core will
199take care of finding the right driver and will call its probe() method.
200If a driver supports different device types, you can specify the type you
201want using the type field. You can also specify an IRQ and platform data
202if needed.
203
204Sometimes you know that a device is connected to a given I2C bus, but you
205don't know the exact address it uses. This happens on TV adapters for
206example, where the same driver supports dozens of slightly different
207models, and I2C device addresses change from one model to the next. In
208that case, you can use the i2c_new_probed_device() variant, which is
209similar to i2c_new_device(), except that it takes an additional list of
210possible I2C addresses to probe. A device is created for the first
211responsive address in the list. If you expect more than one device to be
212present in the address range, simply call i2c_new_probed_device() that
213many times.
214
215The call to i2c_new_device() or i2c_new_probed_device() typically happens
216in the I2C bus driver. You may want to save the returned i2c_client
217reference for later use.
218
219
220Device Deletion (Standard driver model)
221---------------------------------------
222
223Each I2C device which has been created using i2c_new_device() or
224i2c_new_probed_device() can be unregistered by calling
225i2c_unregister_device(). If you don't call it explicitly, it will be
226called automatically before the underlying I2C bus itself is removed, as a
227device can't survive its parent in the device driver model.
228
229
David Brownell4298cfc2007-05-01 23:26:31 +0200230Legacy Driver Binding Model
231---------------------------
232
Linus Torvalds1da177e2005-04-16 15:20:36 -0700233Most i2c devices can be present on several i2c addresses; for some this
234is determined in hardware (by soldering some chip pins to Vcc or Ground),
235for others this can be changed in software (by writing to specific client
236registers). Some devices are usually on a specific address, but not always;
237and some are even more tricky. So you will probably need to scan several
238i2c addresses for your clients, and do some sort of detection to see
239whether it is actually a device supported by your driver.
240
241To give the user a maximum of possibilities, some default module parameters
242are defined to help determine what addresses are scanned. Several macros
243are defined in i2c.h to help you support them, as well as a generic
244detection algorithm.
245
246You do not have to use this parameter interface; but don't try to use
Jean Delvare2ed2dc32005-07-31 21:42:02 +0200247function i2c_probe() if you don't.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700248
Linus Torvalds1da177e2005-04-16 15:20:36 -0700249
David Brownell4298cfc2007-05-01 23:26:31 +0200250Probing classes (Legacy model)
251------------------------------
Linus Torvalds1da177e2005-04-16 15:20:36 -0700252
253All parameters are given as lists of unsigned 16-bit integers. Lists are
254terminated by I2C_CLIENT_END.
255The following lists are used internally:
256
257 normal_i2c: filled in by the module writer.
258 A list of I2C addresses which should normally be examined.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700259 probe: insmod parameter.
260 A list of pairs. The first value is a bus number (-1 for any I2C bus),
261 the second is the address. These addresses are also probed, as if they
262 were in the 'normal' list.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700263 ignore: insmod parameter.
264 A list of pairs. The first value is a bus number (-1 for any I2C bus),
265 the second is the I2C address. These addresses are never probed.
Jean Delvaref4b50262005-07-31 21:49:03 +0200266 This parameter overrules the 'normal_i2c' list only.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700267 force: insmod parameter.
268 A list of pairs. The first value is a bus number (-1 for any I2C bus),
269 the second is the I2C address. A device is blindly assumed to be on
270 the given address, no probing is done.
271
Jean Delvaref4b50262005-07-31 21:49:03 +0200272Additionally, kind-specific force lists may optionally be defined if
273the driver supports several chip kinds. They are grouped in a
274NULL-terminated list of pointers named forces, those first element if the
275generic force list mentioned above. Each additional list correspond to an
276insmod parameter of the form force_<kind>.
277
Jean Delvareb3d54962005-04-02 20:31:02 +0200278Fortunately, as a module writer, you just have to define the `normal_i2c'
279parameter. The complete declaration could look like this:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700280
Jean Delvare2cdddeb2008-01-27 18:14:47 +0100281 /* Scan 0x4c to 0x4f */
282 static const unsigned short normal_i2c[] = { 0x4c, 0x4d, 0x4e, 0x4f,
283 I2C_CLIENT_END };
Linus Torvalds1da177e2005-04-16 15:20:36 -0700284
285 /* Magic definition of all other variables and things */
286 I2C_CLIENT_INSMOD;
Jean Delvaref4b50262005-07-31 21:49:03 +0200287 /* Or, if your driver supports, say, 2 kind of devices: */
288 I2C_CLIENT_INSMOD_2(foo, bar);
289
290If you use the multi-kind form, an enum will be defined for you:
291 enum chips { any_chip, foo, bar, ... }
292You can then (and certainly should) use it in the driver code.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700293
Jean Delvareb3d54962005-04-02 20:31:02 +0200294Note that you *have* to call the defined variable `normal_i2c',
295without any prefix!
Linus Torvalds1da177e2005-04-16 15:20:36 -0700296
297
David Brownell4298cfc2007-05-01 23:26:31 +0200298Attaching to an adapter (Legacy model)
299--------------------------------------
Linus Torvalds1da177e2005-04-16 15:20:36 -0700300
301Whenever a new adapter is inserted, or for all adapters if the driver is
302being registered, the callback attach_adapter() is called. Now is the
303time to determine what devices are present on the adapter, and to register
304a client for each of them.
305
306The attach_adapter callback is really easy: we just call the generic
307detection function. This function will scan the bus for us, using the
308information as defined in the lists explained above. If a device is
309detected at a specific address, another callback is called.
310
311 int foo_attach_adapter(struct i2c_adapter *adapter)
312 {
313 return i2c_probe(adapter,&addr_data,&foo_detect_client);
314 }
315
Linus Torvalds1da177e2005-04-16 15:20:36 -0700316Remember, structure `addr_data' is defined by the macros explained above,
317so you do not have to define it yourself.
318
Jean Delvare2ed2dc32005-07-31 21:42:02 +0200319The i2c_probe function will call the foo_detect_client
Linus Torvalds1da177e2005-04-16 15:20:36 -0700320function only for those i2c addresses that actually have a device on
321them (unless a `force' parameter was used). In addition, addresses that
322are already in use (by some other registered client) are skipped.
323
324
David Brownell4298cfc2007-05-01 23:26:31 +0200325The detect client function (Legacy model)
326-----------------------------------------
Linus Torvalds1da177e2005-04-16 15:20:36 -0700327
Jean Delvare2ed2dc32005-07-31 21:42:02 +0200328The detect client function is called by i2c_probe. The `kind' parameter
329contains -1 for a probed detection, 0 for a forced detection, or a positive
330number for a forced detection with a chip type forced.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700331
Jean Delvarea89ba0b2005-08-09 20:17:55 +0200332Returning an error different from -ENODEV in a detect function will cause
333the detection to stop: other addresses and adapters won't be scanned.
334This should only be done on fatal or internal errors, such as a memory
335shortage or i2c_attach_client failing.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700336
337For now, you can ignore the `flags' parameter. It is there for future use.
338
339 int foo_detect_client(struct i2c_adapter *adapter, int address,
Jean Delvareeefcd752007-05-01 23:26:35 +0200340 int kind)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700341 {
342 int err = 0;
343 int i;
Jean Delvareeefcd752007-05-01 23:26:35 +0200344 struct i2c_client *client;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700345 struct foo_data *data;
Jean Delvareeefcd752007-05-01 23:26:35 +0200346 const char *name = "";
Linus Torvalds1da177e2005-04-16 15:20:36 -0700347
348 /* Let's see whether this adapter can support what we need.
Jean Delvareeefcd752007-05-01 23:26:35 +0200349 Please substitute the things you need here! */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700350 if (!i2c_check_functionality(adapter,I2C_FUNC_SMBUS_WORD_DATA |
351 I2C_FUNC_SMBUS_WRITE_BYTE))
352 goto ERROR0;
353
Linus Torvalds1da177e2005-04-16 15:20:36 -0700354 /* OK. For now, we presume we have a valid client. We now create the
355 client structure, even though we cannot fill it completely yet.
356 But it allows us to access several i2c functions safely */
357
Jean Delvare2445eb62005-10-17 23:16:25 +0200358 if (!(data = kzalloc(sizeof(struct foo_data), GFP_KERNEL))) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700359 err = -ENOMEM;
360 goto ERROR0;
361 }
362
Jean Delvareeefcd752007-05-01 23:26:35 +0200363 client = &data->client;
364 i2c_set_clientdata(client, data);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700365
Jean Delvareeefcd752007-05-01 23:26:35 +0200366 client->addr = address;
367 client->adapter = adapter;
368 client->driver = &foo_driver;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700369
370 /* Now, we do the remaining detection. If no `force' parameter is used. */
371
372 /* First, the generic detection (if any), that is skipped if any force
373 parameter was used. */
374 if (kind < 0) {
375 /* The below is of course bogus */
Jean Delvareeefcd752007-05-01 23:26:35 +0200376 if (foo_read(client, FOO_REG_GENERIC) != FOO_GENERIC_VALUE)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700377 goto ERROR1;
378 }
379
Linus Torvalds1da177e2005-04-16 15:20:36 -0700380 /* Next, specific detection. This is especially important for `sensors'
381 devices. */
382
383 /* Determine the chip type. Not needed if a `force_CHIPTYPE' parameter
384 was used. */
385 if (kind <= 0) {
Jean Delvareeefcd752007-05-01 23:26:35 +0200386 i = foo_read(client, FOO_REG_CHIPTYPE);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700387 if (i == FOO_TYPE_1)
388 kind = chip1; /* As defined in the enum */
389 else if (i == FOO_TYPE_2)
390 kind = chip2;
391 else {
392 printk("foo: Ignoring 'force' parameter for unknown chip at "
393 "adapter %d, address 0x%02x\n",i2c_adapter_id(adapter),address);
394 goto ERROR1;
395 }
396 }
397
398 /* Now set the type and chip names */
399 if (kind == chip1) {
Jean Delvareeefcd752007-05-01 23:26:35 +0200400 name = "chip1";
Linus Torvalds1da177e2005-04-16 15:20:36 -0700401 } else if (kind == chip2) {
Jean Delvareeefcd752007-05-01 23:26:35 +0200402 name = "chip2";
Linus Torvalds1da177e2005-04-16 15:20:36 -0700403 }
404
Linus Torvalds1da177e2005-04-16 15:20:36 -0700405 /* Fill in the remaining client fields. */
Jean Delvareeefcd752007-05-01 23:26:35 +0200406 strlcpy(client->name, name, I2C_NAME_SIZE);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700407 data->type = kind;
Jean Delvareeefcd752007-05-01 23:26:35 +0200408 mutex_init(&data->update_lock); /* Only if you use this field */
Linus Torvalds1da177e2005-04-16 15:20:36 -0700409
410 /* Any other initializations in data must be done here too. */
411
Linus Torvalds1da177e2005-04-16 15:20:36 -0700412 /* This function can write default values to the client registers, if
413 needed. */
Jean Delvareeefcd752007-05-01 23:26:35 +0200414 foo_init_client(client);
415
416 /* Tell the i2c layer a new client has arrived */
417 if ((err = i2c_attach_client(client)))
418 goto ERROR1;
419
Linus Torvalds1da177e2005-04-16 15:20:36 -0700420 return 0;
421
422 /* OK, this is not exactly good programming practice, usually. But it is
423 very code-efficient in this case. */
424
Linus Torvalds1da177e2005-04-16 15:20:36 -0700425 ERROR1:
Jean Delvarea852daa2005-11-02 21:42:48 +0100426 kfree(data);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700427 ERROR0:
428 return err;
429 }
430
431
David Brownell4298cfc2007-05-01 23:26:31 +0200432Removing the client (Legacy model)
433==================================
Linus Torvalds1da177e2005-04-16 15:20:36 -0700434
435The detach_client call back function is called when a client should be
436removed. It may actually fail, but only when panicking. This code is
437much simpler than the attachment code, fortunately!
438
439 int foo_detach_client(struct i2c_client *client)
440 {
Jean Delvareeefcd752007-05-01 23:26:35 +0200441 int err;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700442
443 /* Try to detach the client from i2c space */
Jean Delvare7bef5592005-07-27 22:14:49 +0200444 if ((err = i2c_detach_client(client)))
Linus Torvalds1da177e2005-04-16 15:20:36 -0700445 return err;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700446
Jean Delvarea852daa2005-11-02 21:42:48 +0100447 kfree(i2c_get_clientdata(client));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700448 return 0;
449 }
450
451
452Initializing the module or kernel
453=================================
454
455When the kernel is booted, or when your foo driver module is inserted,
456you have to do some initializing. Fortunately, just attaching (registering)
457the driver module is usually enough.
458
Linus Torvalds1da177e2005-04-16 15:20:36 -0700459 static int __init foo_init(void)
460 {
461 int res;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700462
463 if ((res = i2c_add_driver(&foo_driver))) {
464 printk("foo: Driver registration failed, module not inserted.\n");
Linus Torvalds1da177e2005-04-16 15:20:36 -0700465 return res;
466 }
Linus Torvalds1da177e2005-04-16 15:20:36 -0700467 return 0;
468 }
469
Jean Delvareeefcd752007-05-01 23:26:35 +0200470 static void __exit foo_cleanup(void)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700471 {
Jean Delvareeefcd752007-05-01 23:26:35 +0200472 i2c_del_driver(&foo_driver);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700473 }
474
475 /* Substitute your own name and email address */
476 MODULE_AUTHOR("Frodo Looijaard <frodol@dds.nl>"
477 MODULE_DESCRIPTION("Driver for Barf Inc. Foo I2C devices");
478
Jean Delvareeefcd752007-05-01 23:26:35 +0200479 /* a few non-GPL license types are also allowed */
480 MODULE_LICENSE("GPL");
481
Linus Torvalds1da177e2005-04-16 15:20:36 -0700482 module_init(foo_init);
483 module_exit(foo_cleanup);
484
485Note that some functions are marked by `__init', and some data structures
Jean Delvareeefcd752007-05-01 23:26:35 +0200486by `__initdata'. These functions and structures can be removed after
Linus Torvalds1da177e2005-04-16 15:20:36 -0700487kernel booting (or module loading) is completed.
488
Jean Delvarefb687d72005-12-18 16:51:55 +0100489
David Brownellf37dd802007-02-13 22:09:00 +0100490Power Management
491================
492
493If your I2C device needs special handling when entering a system low
494power state -- like putting a transceiver into a low power mode, or
495activating a system wakeup mechanism -- do that in the suspend() method.
496The resume() method should reverse what the suspend() method does.
497
498These are standard driver model calls, and they work just like they
499would for any other driver stack. The calls can sleep, and can use
500I2C messaging to the device being suspended or resumed (since their
501parent I2C adapter is active when these calls are issued, and IRQs
502are still enabled).
503
504
505System Shutdown
506===============
507
508If your I2C device needs special handling when the system shuts down
509or reboots (including kexec) -- like turning something off -- use a
510shutdown() method.
511
512Again, this is a standard driver model call, working just like it
513would for any other driver stack: the calls can sleep, and can use
514I2C messaging.
515
516
Linus Torvalds1da177e2005-04-16 15:20:36 -0700517Command function
518================
519
520A generic ioctl-like function call back is supported. You will seldom
Jean Delvarefb687d72005-12-18 16:51:55 +0100521need this, and its use is deprecated anyway, so newer design should not
522use it. Set it to NULL.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700523
524
525Sending and receiving
526=====================
527
528If you want to communicate with your device, there are several functions
529to do this. You can find all of them in i2c.h.
530
531If you can choose between plain i2c communication and SMBus level
532communication, please use the last. All adapters understand SMBus level
533commands, but only some of them understand plain i2c!
534
535
536Plain i2c communication
537-----------------------
538
539 extern int i2c_master_send(struct i2c_client *,const char* ,int);
540 extern int i2c_master_recv(struct i2c_client *,char* ,int);
541
542These routines read and write some bytes from/to a client. The client
543contains the i2c address, so you do not have to include it. The second
544parameter contains the bytes the read/write, the third the length of the
545buffer. Returned is the actual number of bytes read/written.
546
547 extern int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msg,
548 int num);
549
550This sends a series of messages. Each message can be a read or write,
551and they can be mixed in any way. The transactions are combined: no
552stop bit is sent between transaction. The i2c_msg structure contains
553for each message the client address, the number of bytes of the message
554and the message data itself.
555
556You can read the file `i2c-protocol' for more information about the
557actual i2c protocol.
558
559
560SMBus communication
561-------------------
562
563 extern s32 i2c_smbus_xfer (struct i2c_adapter * adapter, u16 addr,
564 unsigned short flags,
565 char read_write, u8 command, int size,
566 union i2c_smbus_data * data);
567
568 This is the generic SMBus function. All functions below are implemented
569 in terms of it. Never use this function directly!
570
571
Linus Torvalds1da177e2005-04-16 15:20:36 -0700572 extern s32 i2c_smbus_read_byte(struct i2c_client * client);
573 extern s32 i2c_smbus_write_byte(struct i2c_client * client, u8 value);
574 extern s32 i2c_smbus_read_byte_data(struct i2c_client * client, u8 command);
575 extern s32 i2c_smbus_write_byte_data(struct i2c_client * client,
576 u8 command, u8 value);
577 extern s32 i2c_smbus_read_word_data(struct i2c_client * client, u8 command);
578 extern s32 i2c_smbus_write_word_data(struct i2c_client * client,
579 u8 command, u16 value);
Jean Delvare67c2e662008-07-14 22:38:23 +0200580 extern s32 i2c_smbus_read_block_data(struct i2c_client * client,
581 u8 command, u8 *values);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700582 extern s32 i2c_smbus_write_block_data(struct i2c_client * client,
583 u8 command, u8 length,
584 u8 *values);
Jean Delvare7865e242005-10-08 00:00:31 +0200585 extern s32 i2c_smbus_read_i2c_block_data(struct i2c_client * client,
Jean Delvare4b2643d2007-07-12 14:12:29 +0200586 u8 command, u8 length, u8 *values);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700587 extern s32 i2c_smbus_write_i2c_block_data(struct i2c_client * client,
588 u8 command, u8 length,
589 u8 *values);
Jean Delvare67c2e662008-07-14 22:38:23 +0200590
591These ones were removed from i2c-core because they had no users, but could
592be added back later if needed:
593
594 extern s32 i2c_smbus_write_quick(struct i2c_client * client, u8 value);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700595 extern s32 i2c_smbus_process_call(struct i2c_client * client,
596 u8 command, u16 value);
597 extern s32 i2c_smbus_block_process_call(struct i2c_client *client,
598 u8 command, u8 length,
599 u8 *values)
600
David Brownell24a5bb72008-07-14 22:38:23 +0200601All these transactions return a negative errno value on failure. The 'write'
602transactions return 0 on success; the 'read' transactions return the read
603value, except for block transactions, which return the number of values
604read. The block buffers need not be longer than 32 bytes.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700605
606You can read the file `smbus-protocol' for more information about the
607actual SMBus protocol.
608
609
610General purpose routines
611========================
612
613Below all general purpose routines are listed, that were not mentioned
614before.
615
Jean Delvareeefcd752007-05-01 23:26:35 +0200616 /* This call returns a unique low identifier for each registered adapter.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700617 */
618 extern int i2c_adapter_id(struct i2c_adapter *adap);
619