Commit | Line | Data |
---|---|---|
1da177e4 | 1 | This is a small guide for those who want to write kernel drivers for I2C |
4298cfc3 | 2 | or SMBus devices, using Linux as the protocol host/master (not slave). |
1da177e4 LT |
3 | |
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! | |
7 | ||
8 | ||
9 | General remarks | |
10 | =============== | |
11 | ||
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. | |
17 | ||
18 | ||
19 | The driver structure | |
20 | ==================== | |
21 | ||
22 | Usually, you will implement a single driver structure, and instantiate | |
23 | all clients from it. Remember, a driver structure contains general access | |
f37dd80a DB |
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. | |
1da177e4 | 27 | |
2260e63a BD |
28 | /* iff driver uses driver model ("new style") binding model: */ |
29 | ||
30 | static struct i2c_device_id foo_idtable[] = { | |
31 | { "foo", my_id_for_foo }, | |
32 | { "bar", my_id_for_bar }, | |
33 | { } | |
34 | }; | |
35 | ||
36 | MODULE_DEVICE_TABLE(i2c, foo_idtable); | |
37 | ||
1da177e4 | 38 | static struct i2c_driver foo_driver = { |
d45d204f | 39 | .driver = { |
d45d204f JD |
40 | .name = "foo", |
41 | }, | |
4298cfc3 DB |
42 | |
43 | /* iff driver uses driver model ("new style") binding model: */ | |
2260e63a | 44 | .id_table = foo_ids, |
4298cfc3 DB |
45 | .probe = foo_probe, |
46 | .remove = foo_remove, | |
47 | ||
48 | /* else, driver uses "legacy" binding model: */ | |
f37dd80a DB |
49 | .attach_adapter = foo_attach_adapter, |
50 | .detach_client = foo_detach_client, | |
4298cfc3 DB |
51 | |
52 | /* these may be used regardless of the driver binding model */ | |
f37dd80a DB |
53 | .shutdown = foo_shutdown, /* optional */ |
54 | .suspend = foo_suspend, /* optional */ | |
55 | .resume = foo_resume, /* optional */ | |
56 | .command = foo_command, /* optional */ | |
1da177e4 LT |
57 | } |
58 | ||
f37dd80a DB |
59 | The name field is the driver name, and must not contain spaces. It |
60 | should match the module name (if the driver can be compiled as a module), | |
61 | although you can use MODULE_ALIAS (passing "foo" in this example) to add | |
4298cfc3 DB |
62 | another name for the module. If the driver name doesn't match the module |
63 | name, the module won't be automatically loaded (hotplug/coldplug). | |
1da177e4 | 64 | |
1da177e4 LT |
65 | All other fields are for call-back functions which will be explained |
66 | below. | |
67 | ||
1da177e4 LT |
68 | |
69 | Extra client data | |
70 | ================= | |
71 | ||
f37dd80a DB |
72 | Each client structure has a special `data' field that can point to any |
73 | structure at all. You should use this to keep device-specific data, | |
74 | especially in drivers that handle multiple I2C or SMBUS devices. You | |
1da177e4 LT |
75 | do not always need this, but especially for `sensors' drivers, it can |
76 | be very useful. | |
77 | ||
f37dd80a DB |
78 | /* 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 | ||
1da177e4 LT |
84 | An example structure is below. |
85 | ||
86 | struct foo_data { | |
2445eb62 | 87 | struct i2c_client client; |
1da177e4 LT |
88 | 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. */ | |
eefcd75e | 94 | struct mutex update_lock; /* When we are reading lots of information, |
1da177e4 LT |
95 | 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 | ||
103 | Accessing the client | |
104 | ==================== | |
105 | ||
106 | Let's say we have a valid client structure. At some time, we will need | |
107 | to gather information from the client, or write new information to the | |
108 | client. How we will export this information to user-space is less | |
109 | important at this moment (perhaps we do not need to do this at all for | |
110 | some obscure clients). But we need generic reading and writing routines. | |
111 | ||
112 | I have found it useful to define foo_read and foo_write function for this. | |
113 | For some cases, it will be easier to call the i2c functions directly, | |
114 | but many chips have some kind of register-value idea that can easily | |
eefcd75e | 115 | be encapsulated. |
1da177e4 LT |
116 | |
117 | The below functions are simple examples, and should not be copied | |
118 | literally. | |
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 | ||
1da177e4 LT |
138 | |
139 | Probing and attaching | |
140 | ===================== | |
141 | ||
4298cfc3 DB |
142 | The Linux I2C stack was originally written to support access to hardware |
143 | monitoring chips on PC motherboards, and thus it embeds some assumptions | |
144 | that are more appropriate to SMBus (and PCs) than to I2C. One of these | |
145 | assumptions is that most adapters and devices drivers support the SMBUS_QUICK | |
146 | protocol to probe device presence. Another is that devices and their drivers | |
147 | can be sufficiently configured using only such probe primitives. | |
148 | ||
149 | As Linux and its I2C stack became more widely used in embedded systems | |
150 | and complex components such as DVB adapters, those assumptions became more | |
151 | problematic. Drivers for I2C devices that issue interrupts need more (and | |
152 | different) configuration information, as do drivers handling chip variants | |
153 | that can't be distinguished by protocol probing, or which need some board | |
154 | specific information to operate correctly. | |
155 | ||
156 | Accordingly, the I2C stack now has two models for associating I2C devices | |
157 | with their drivers: the original "legacy" model, and a newer one that's | |
158 | fully compatible with the Linux 2.6 driver model. These models do not mix, | |
159 | since the "legacy" model requires drivers to create "i2c_client" device | |
160 | objects after SMBus style probing, while the Linux driver model expects | |
161 | drivers to be given such device objects in their probe() routines. | |
162 | ||
163 | ||
164 | Standard Driver Model Binding ("New Style") | |
165 | ------------------------------------------- | |
166 | ||
167 | System infrastructure, typically board-specific initialization code or | |
168 | boot firmware, reports what I2C devices exist. For example, there may be | |
169 | a table, in the kernel or from the boot loader, identifying I2C devices | |
170 | and linking them to board-specific configuration information about IRQs | |
171 | and other wiring artifacts, chip type, and so on. That could be used to | |
172 | create i2c_client objects for each I2C device. | |
173 | ||
174 | I2C device drivers using this binding model work just like any other | |
175 | kind of driver in Linux: they provide a probe() method to bind to | |
176 | those devices, and a remove() method to unbind. | |
177 | ||
d2653e92 JD |
178 | static int foo_probe(struct i2c_client *client, |
179 | const struct i2c_device_id *id); | |
4298cfc3 DB |
180 | static int foo_remove(struct i2c_client *client); |
181 | ||
182 | Remember that the i2c_driver does not create those client handles. The | |
183 | handle 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 | |
185 | foo_remove() returns. That binding model is used by most Linux drivers. | |
186 | ||
2260e63a BD |
187 | The probe function is called when an entry in the id_table name field |
188 | matches the device's name. It is passed the entry that was matched so | |
189 | the driver knows which one in the table matched. | |
4298cfc3 DB |
190 | |
191 | ||
ce9e0794 JD |
192 | Device Creation (Standard driver model) |
193 | --------------------------------------- | |
194 | ||
195 | If you know for a fact that an I2C device is connected to a given I2C bus, | |
196 | you can instantiate that device by simply filling an i2c_board_info | |
197 | structure with the device address and driver name, and calling | |
198 | i2c_new_device(). This will create the device, then the driver core will | |
199 | take care of finding the right driver and will call its probe() method. | |
200 | If a driver supports different device types, you can specify the type you | |
201 | want using the type field. You can also specify an IRQ and platform data | |
202 | if needed. | |
203 | ||
204 | Sometimes you know that a device is connected to a given I2C bus, but you | |
205 | don't know the exact address it uses. This happens on TV adapters for | |
206 | example, where the same driver supports dozens of slightly different | |
207 | models, and I2C device addresses change from one model to the next. In | |
208 | that case, you can use the i2c_new_probed_device() variant, which is | |
209 | similar to i2c_new_device(), except that it takes an additional list of | |
210 | possible I2C addresses to probe. A device is created for the first | |
211 | responsive address in the list. If you expect more than one device to be | |
212 | present in the address range, simply call i2c_new_probed_device() that | |
213 | many times. | |
214 | ||
215 | The call to i2c_new_device() or i2c_new_probed_device() typically happens | |
216 | in the I2C bus driver. You may want to save the returned i2c_client | |
217 | reference for later use. | |
218 | ||
219 | ||
220 | Device Deletion (Standard driver model) | |
221 | --------------------------------------- | |
222 | ||
223 | Each I2C device which has been created using i2c_new_device() or | |
224 | i2c_new_probed_device() can be unregistered by calling | |
225 | i2c_unregister_device(). If you don't call it explicitly, it will be | |
226 | called automatically before the underlying I2C bus itself is removed, as a | |
227 | device can't survive its parent in the device driver model. | |
228 | ||
229 | ||
4298cfc3 DB |
230 | Legacy Driver Binding Model |
231 | --------------------------- | |
232 | ||
1da177e4 LT |
233 | Most i2c devices can be present on several i2c addresses; for some this |
234 | is determined in hardware (by soldering some chip pins to Vcc or Ground), | |
235 | for others this can be changed in software (by writing to specific client | |
236 | registers). Some devices are usually on a specific address, but not always; | |
237 | and some are even more tricky. So you will probably need to scan several | |
238 | i2c addresses for your clients, and do some sort of detection to see | |
239 | whether it is actually a device supported by your driver. | |
240 | ||
241 | To give the user a maximum of possibilities, some default module parameters | |
242 | are defined to help determine what addresses are scanned. Several macros | |
243 | are defined in i2c.h to help you support them, as well as a generic | |
244 | detection algorithm. | |
245 | ||
246 | You do not have to use this parameter interface; but don't try to use | |
2ed2dc3c | 247 | function i2c_probe() if you don't. |
1da177e4 | 248 | |
1da177e4 | 249 | |
4298cfc3 DB |
250 | Probing classes (Legacy model) |
251 | ------------------------------ | |
1da177e4 LT |
252 | |
253 | All parameters are given as lists of unsigned 16-bit integers. Lists are | |
254 | terminated by I2C_CLIENT_END. | |
255 | The 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. | |
1da177e4 LT |
259 | 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. | |
1da177e4 LT |
263 | 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. | |
f4b50261 | 266 | This parameter overrules the 'normal_i2c' list only. |
1da177e4 LT |
267 | 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 | ||
f4b50261 JD |
272 | Additionally, kind-specific force lists may optionally be defined if |
273 | the driver supports several chip kinds. They are grouped in a | |
274 | NULL-terminated list of pointers named forces, those first element if the | |
275 | generic force list mentioned above. Each additional list correspond to an | |
276 | insmod parameter of the form force_<kind>. | |
277 | ||
b3d5496e JD |
278 | Fortunately, as a module writer, you just have to define the `normal_i2c' |
279 | parameter. The complete declaration could look like this: | |
1da177e4 | 280 | |
2cdddeb8 JD |
281 | /* Scan 0x4c to 0x4f */ |
282 | static const unsigned short normal_i2c[] = { 0x4c, 0x4d, 0x4e, 0x4f, | |
283 | I2C_CLIENT_END }; | |
1da177e4 LT |
284 | |
285 | /* Magic definition of all other variables and things */ | |
286 | I2C_CLIENT_INSMOD; | |
f4b50261 JD |
287 | /* Or, if your driver supports, say, 2 kind of devices: */ |
288 | I2C_CLIENT_INSMOD_2(foo, bar); | |
289 | ||
290 | If you use the multi-kind form, an enum will be defined for you: | |
291 | enum chips { any_chip, foo, bar, ... } | |
292 | You can then (and certainly should) use it in the driver code. | |
1da177e4 | 293 | |
b3d5496e JD |
294 | Note that you *have* to call the defined variable `normal_i2c', |
295 | without any prefix! | |
1da177e4 LT |
296 | |
297 | ||
4298cfc3 DB |
298 | Attaching to an adapter (Legacy model) |
299 | -------------------------------------- | |
1da177e4 LT |
300 | |
301 | Whenever a new adapter is inserted, or for all adapters if the driver is | |
302 | being registered, the callback attach_adapter() is called. Now is the | |
303 | time to determine what devices are present on the adapter, and to register | |
304 | a client for each of them. | |
305 | ||
306 | The attach_adapter callback is really easy: we just call the generic | |
307 | detection function. This function will scan the bus for us, using the | |
308 | information as defined in the lists explained above. If a device is | |
309 | detected 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 | ||
1da177e4 LT |
316 | Remember, structure `addr_data' is defined by the macros explained above, |
317 | so you do not have to define it yourself. | |
318 | ||
2ed2dc3c | 319 | The i2c_probe function will call the foo_detect_client |
1da177e4 LT |
320 | function only for those i2c addresses that actually have a device on |
321 | them (unless a `force' parameter was used). In addition, addresses that | |
322 | are already in use (by some other registered client) are skipped. | |
323 | ||
324 | ||
4298cfc3 DB |
325 | The detect client function (Legacy model) |
326 | ----------------------------------------- | |
1da177e4 | 327 | |
2ed2dc3c JD |
328 | The detect client function is called by i2c_probe. The `kind' parameter |
329 | contains -1 for a probed detection, 0 for a forced detection, or a positive | |
330 | number for a forced detection with a chip type forced. | |
1da177e4 | 331 | |
a89ba0bc JD |
332 | Returning an error different from -ENODEV in a detect function will cause |
333 | the detection to stop: other addresses and adapters won't be scanned. | |
334 | This should only be done on fatal or internal errors, such as a memory | |
335 | shortage or i2c_attach_client failing. | |
1da177e4 LT |
336 | |
337 | For 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, | |
eefcd75e | 340 | int kind) |
1da177e4 LT |
341 | { |
342 | int err = 0; | |
343 | int i; | |
eefcd75e | 344 | struct i2c_client *client; |
1da177e4 | 345 | struct foo_data *data; |
eefcd75e | 346 | const char *name = ""; |
1da177e4 LT |
347 | |
348 | /* Let's see whether this adapter can support what we need. | |
eefcd75e | 349 | Please substitute the things you need here! */ |
1da177e4 LT |
350 | if (!i2c_check_functionality(adapter,I2C_FUNC_SMBUS_WORD_DATA | |
351 | I2C_FUNC_SMBUS_WRITE_BYTE)) | |
352 | goto ERROR0; | |
353 | ||
1da177e4 LT |
354 | /* 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 | ||
2445eb62 | 358 | if (!(data = kzalloc(sizeof(struct foo_data), GFP_KERNEL))) { |
1da177e4 LT |
359 | err = -ENOMEM; |
360 | goto ERROR0; | |
361 | } | |
362 | ||
eefcd75e JD |
363 | client = &data->client; |
364 | i2c_set_clientdata(client, data); | |
1da177e4 | 365 | |
eefcd75e JD |
366 | client->addr = address; |
367 | client->adapter = adapter; | |
368 | client->driver = &foo_driver; | |
1da177e4 LT |
369 | |
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 */ | |
eefcd75e | 376 | if (foo_read(client, FOO_REG_GENERIC) != FOO_GENERIC_VALUE) |
1da177e4 LT |
377 | goto ERROR1; |
378 | } | |
379 | ||
1da177e4 LT |
380 | /* 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) { | |
eefcd75e | 386 | i = foo_read(client, FOO_REG_CHIPTYPE); |
1da177e4 LT |
387 | 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) { | |
eefcd75e | 400 | name = "chip1"; |
1da177e4 | 401 | } else if (kind == chip2) { |
eefcd75e | 402 | name = "chip2"; |
1da177e4 LT |
403 | } |
404 | ||
1da177e4 | 405 | /* Fill in the remaining client fields. */ |
eefcd75e | 406 | strlcpy(client->name, name, I2C_NAME_SIZE); |
1da177e4 | 407 | data->type = kind; |
eefcd75e | 408 | mutex_init(&data->update_lock); /* Only if you use this field */ |
1da177e4 LT |
409 | |
410 | /* Any other initializations in data must be done here too. */ | |
411 | ||
1da177e4 LT |
412 | /* This function can write default values to the client registers, if |
413 | needed. */ | |
eefcd75e JD |
414 | 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 | ||
1da177e4 LT |
420 | return 0; |
421 | ||
422 | /* OK, this is not exactly good programming practice, usually. But it is | |
423 | very code-efficient in this case. */ | |
424 | ||
1da177e4 | 425 | ERROR1: |
a852daa0 | 426 | kfree(data); |
1da177e4 LT |
427 | ERROR0: |
428 | return err; | |
429 | } | |
430 | ||
431 | ||
4298cfc3 DB |
432 | Removing the client (Legacy model) |
433 | ================================== | |
1da177e4 LT |
434 | |
435 | The detach_client call back function is called when a client should be | |
436 | removed. It may actually fail, but only when panicking. This code is | |
437 | much simpler than the attachment code, fortunately! | |
438 | ||
439 | int foo_detach_client(struct i2c_client *client) | |
440 | { | |
eefcd75e | 441 | int err; |
1da177e4 LT |
442 | |
443 | /* Try to detach the client from i2c space */ | |
7bef5594 | 444 | if ((err = i2c_detach_client(client))) |
1da177e4 | 445 | return err; |
1da177e4 | 446 | |
a852daa0 | 447 | kfree(i2c_get_clientdata(client)); |
1da177e4 LT |
448 | return 0; |
449 | } | |
450 | ||
451 | ||
452 | Initializing the module or kernel | |
453 | ================================= | |
454 | ||
455 | When the kernel is booted, or when your foo driver module is inserted, | |
456 | you have to do some initializing. Fortunately, just attaching (registering) | |
457 | the driver module is usually enough. | |
458 | ||
1da177e4 LT |
459 | static int __init foo_init(void) |
460 | { | |
461 | int res; | |
1da177e4 LT |
462 | |
463 | if ((res = i2c_add_driver(&foo_driver))) { | |
464 | printk("foo: Driver registration failed, module not inserted.\n"); | |
1da177e4 LT |
465 | return res; |
466 | } | |
1da177e4 LT |
467 | return 0; |
468 | } | |
469 | ||
eefcd75e | 470 | static void __exit foo_cleanup(void) |
1da177e4 | 471 | { |
eefcd75e | 472 | i2c_del_driver(&foo_driver); |
1da177e4 LT |
473 | } |
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 | ||
eefcd75e JD |
479 | /* a few non-GPL license types are also allowed */ |
480 | MODULE_LICENSE("GPL"); | |
481 | ||
1da177e4 LT |
482 | module_init(foo_init); |
483 | module_exit(foo_cleanup); | |
484 | ||
485 | Note that some functions are marked by `__init', and some data structures | |
eefcd75e | 486 | by `__initdata'. These functions and structures can be removed after |
1da177e4 LT |
487 | kernel booting (or module loading) is completed. |
488 | ||
fb687d73 | 489 | |
f37dd80a DB |
490 | Power Management |
491 | ================ | |
492 | ||
493 | If your I2C device needs special handling when entering a system low | |
494 | power state -- like putting a transceiver into a low power mode, or | |
495 | activating a system wakeup mechanism -- do that in the suspend() method. | |
496 | The resume() method should reverse what the suspend() method does. | |
497 | ||
498 | These are standard driver model calls, and they work just like they | |
499 | would for any other driver stack. The calls can sleep, and can use | |
500 | I2C messaging to the device being suspended or resumed (since their | |
501 | parent I2C adapter is active when these calls are issued, and IRQs | |
502 | are still enabled). | |
503 | ||
504 | ||
505 | System Shutdown | |
506 | =============== | |
507 | ||
508 | If your I2C device needs special handling when the system shuts down | |
509 | or reboots (including kexec) -- like turning something off -- use a | |
510 | shutdown() method. | |
511 | ||
512 | Again, this is a standard driver model call, working just like it | |
513 | would for any other driver stack: the calls can sleep, and can use | |
514 | I2C messaging. | |
515 | ||
516 | ||
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517 | Command function |
518 | ================ | |
519 | ||
520 | A generic ioctl-like function call back is supported. You will seldom | |
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521 | need this, and its use is deprecated anyway, so newer design should not |
522 | use it. Set it to NULL. | |
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523 | |
524 | ||
525 | Sending and receiving | |
526 | ===================== | |
527 | ||
528 | If you want to communicate with your device, there are several functions | |
529 | to do this. You can find all of them in i2c.h. | |
530 | ||
531 | If you can choose between plain i2c communication and SMBus level | |
532 | communication, please use the last. All adapters understand SMBus level | |
533 | commands, but only some of them understand plain i2c! | |
534 | ||
535 | ||
536 | Plain 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 | ||
542 | These routines read and write some bytes from/to a client. The client | |
543 | contains the i2c address, so you do not have to include it. The second | |
544 | parameter contains the bytes the read/write, the third the length of the | |
545 | buffer. 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 | ||
550 | This sends a series of messages. Each message can be a read or write, | |
551 | and they can be mixed in any way. The transactions are combined: no | |
552 | stop bit is sent between transaction. The i2c_msg structure contains | |
553 | for each message the client address, the number of bytes of the message | |
554 | and the message data itself. | |
555 | ||
556 | You can read the file `i2c-protocol' for more information about the | |
557 | actual i2c protocol. | |
558 | ||
559 | ||
560 | SMBus 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 | ||
572 | extern s32 i2c_smbus_write_quick(struct i2c_client * client, u8 value); | |
573 | extern s32 i2c_smbus_read_byte(struct i2c_client * client); | |
574 | extern s32 i2c_smbus_write_byte(struct i2c_client * client, u8 value); | |
575 | extern s32 i2c_smbus_read_byte_data(struct i2c_client * client, u8 command); | |
576 | extern s32 i2c_smbus_write_byte_data(struct i2c_client * client, | |
577 | u8 command, u8 value); | |
578 | extern s32 i2c_smbus_read_word_data(struct i2c_client * client, u8 command); | |
579 | extern s32 i2c_smbus_write_word_data(struct i2c_client * client, | |
580 | u8 command, u16 value); | |
581 | extern s32 i2c_smbus_write_block_data(struct i2c_client * client, | |
582 | u8 command, u8 length, | |
583 | u8 *values); | |
7865e249 | 584 | extern s32 i2c_smbus_read_i2c_block_data(struct i2c_client * client, |
4b2643d7 | 585 | u8 command, u8 length, u8 *values); |
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586 | |
587 | These ones were removed in Linux 2.6.10 because they had no users, but could | |
588 | be added back later if needed: | |
589 | ||
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590 | extern s32 i2c_smbus_read_block_data(struct i2c_client * client, |
591 | u8 command, u8 *values); | |
592 | extern s32 i2c_smbus_write_i2c_block_data(struct i2c_client * client, | |
593 | u8 command, u8 length, | |
594 | u8 *values); | |
595 | 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 | ||
601 | All these transactions return -1 on failure. The 'write' transactions | |
602 | return 0 on success; the 'read' transactions return the read value, except | |
603 | for read_block, which returns the number of values read. The block buffers | |
604 | need not be longer than 32 bytes. | |
605 | ||
606 | You can read the file `smbus-protocol' for more information about the | |
607 | actual SMBus protocol. | |
608 | ||
609 | ||
610 | General purpose routines | |
611 | ======================== | |
612 | ||
613 | Below all general purpose routines are listed, that were not mentioned | |
614 | before. | |
615 | ||
eefcd75e | 616 | /* This call returns a unique low identifier for each registered adapter. |
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617 | */ |
618 | extern int i2c_adapter_id(struct i2c_adapter *adap); | |
619 |