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 LT |
27 | |
28 | static struct i2c_driver foo_driver = { | |
d45d204f | 29 | .driver = { |
d45d204f JD |
30 | .name = "foo", |
31 | }, | |
4298cfc3 DB |
32 | |
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: */ | |
f37dd80a DB |
38 | .attach_adapter = foo_attach_adapter, |
39 | .detach_client = foo_detach_client, | |
4298cfc3 DB |
40 | |
41 | /* these may be used regardless of the driver binding model */ | |
f37dd80a DB |
42 | .shutdown = foo_shutdown, /* optional */ |
43 | .suspend = foo_suspend, /* optional */ | |
44 | .resume = foo_resume, /* optional */ | |
45 | .command = foo_command, /* optional */ | |
1da177e4 LT |
46 | } |
47 | ||
f37dd80a DB |
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 | |
4298cfc3 DB |
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). | |
1da177e4 | 53 | |
1da177e4 LT |
54 | All other fields are for call-back functions which will be explained |
55 | below. | |
56 | ||
1da177e4 LT |
57 | |
58 | Extra client data | |
59 | ================= | |
60 | ||
f37dd80a DB |
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 | |
1da177e4 LT |
64 | do not always need this, but especially for `sensors' drivers, it can |
65 | be very useful. | |
66 | ||
f37dd80a DB |
67 | /* 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 | ||
1da177e4 LT |
73 | An example structure is below. |
74 | ||
75 | struct foo_data { | |
2445eb62 | 76 | struct i2c_client client; |
1da177e4 LT |
77 | 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. */ | |
eefcd75e | 83 | struct mutex update_lock; /* When we are reading lots of information, |
1da177e4 LT |
84 | 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 | ||
92 | Accessing the client | |
93 | ==================== | |
94 | ||
95 | Let's say we have a valid client structure. At some time, we will need | |
96 | to gather information from the client, or write new information to the | |
97 | client. How we will export this information to user-space is less | |
98 | important at this moment (perhaps we do not need to do this at all for | |
99 | some obscure clients). But we need generic reading and writing routines. | |
100 | ||
101 | I have found it useful to define foo_read and foo_write function for this. | |
102 | For some cases, it will be easier to call the i2c functions directly, | |
103 | but many chips have some kind of register-value idea that can easily | |
eefcd75e | 104 | be encapsulated. |
1da177e4 LT |
105 | |
106 | The below functions are simple examples, and should not be copied | |
107 | literally. | |
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 | ||
1da177e4 LT |
127 | |
128 | Probing and attaching | |
129 | ===================== | |
130 | ||
4298cfc3 DB |
131 | The Linux I2C stack was originally written to support access to hardware |
132 | monitoring chips on PC motherboards, and thus it embeds some assumptions | |
133 | that are more appropriate to SMBus (and PCs) than to I2C. One of these | |
134 | assumptions is that most adapters and devices drivers support the SMBUS_QUICK | |
135 | protocol to probe device presence. Another is that devices and their drivers | |
136 | can be sufficiently configured using only such probe primitives. | |
137 | ||
138 | As Linux and its I2C stack became more widely used in embedded systems | |
139 | and complex components such as DVB adapters, those assumptions became more | |
140 | problematic. Drivers for I2C devices that issue interrupts need more (and | |
141 | different) configuration information, as do drivers handling chip variants | |
142 | that can't be distinguished by protocol probing, or which need some board | |
143 | specific information to operate correctly. | |
144 | ||
145 | Accordingly, the I2C stack now has two models for associating I2C devices | |
146 | with their drivers: the original "legacy" model, and a newer one that's | |
147 | fully compatible with the Linux 2.6 driver model. These models do not mix, | |
148 | since the "legacy" model requires drivers to create "i2c_client" device | |
149 | objects after SMBus style probing, while the Linux driver model expects | |
150 | drivers to be given such device objects in their probe() routines. | |
151 | ||
152 | ||
153 | Standard Driver Model Binding ("New Style") | |
154 | ------------------------------------------- | |
155 | ||
156 | System infrastructure, typically board-specific initialization code or | |
157 | boot firmware, reports what I2C devices exist. For example, there may be | |
158 | a table, in the kernel or from the boot loader, identifying I2C devices | |
159 | and linking them to board-specific configuration information about IRQs | |
160 | and other wiring artifacts, chip type, and so on. That could be used to | |
161 | create i2c_client objects for each I2C device. | |
162 | ||
163 | I2C device drivers using this binding model work just like any other | |
164 | kind of driver in Linux: they provide a probe() method to bind to | |
165 | those 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 | ||
170 | Remember that the i2c_driver does not create those client handles. The | |
171 | handle 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 | |
173 | foo_remove() returns. That binding model is used by most Linux drivers. | |
174 | ||
175 | Drivers match devices when i2c_client.driver_name and the driver name are | |
176 | the same; this approach is used in several other busses that don't have | |
177 | device typing support in the hardware. The driver and module name should | |
178 | match, so hotplug/coldplug mechanisms will modprobe the driver. | |
179 | ||
180 | ||
ce9e0794 JD |
181 | Device Creation (Standard driver model) |
182 | --------------------------------------- | |
183 | ||
184 | If you know for a fact that an I2C device is connected to a given I2C bus, | |
185 | you can instantiate that device by simply filling an i2c_board_info | |
186 | structure with the device address and driver name, and calling | |
187 | i2c_new_device(). This will create the device, then the driver core will | |
188 | take care of finding the right driver and will call its probe() method. | |
189 | If a driver supports different device types, you can specify the type you | |
190 | want using the type field. You can also specify an IRQ and platform data | |
191 | if needed. | |
192 | ||
193 | Sometimes you know that a device is connected to a given I2C bus, but you | |
194 | don't know the exact address it uses. This happens on TV adapters for | |
195 | example, where the same driver supports dozens of slightly different | |
196 | models, and I2C device addresses change from one model to the next. In | |
197 | that case, you can use the i2c_new_probed_device() variant, which is | |
198 | similar to i2c_new_device(), except that it takes an additional list of | |
199 | possible I2C addresses to probe. A device is created for the first | |
200 | responsive address in the list. If you expect more than one device to be | |
201 | present in the address range, simply call i2c_new_probed_device() that | |
202 | many times. | |
203 | ||
204 | The call to i2c_new_device() or i2c_new_probed_device() typically happens | |
205 | in the I2C bus driver. You may want to save the returned i2c_client | |
206 | reference for later use. | |
207 | ||
208 | ||
209 | Device Deletion (Standard driver model) | |
210 | --------------------------------------- | |
211 | ||
212 | Each I2C device which has been created using i2c_new_device() or | |
213 | i2c_new_probed_device() can be unregistered by calling | |
214 | i2c_unregister_device(). If you don't call it explicitly, it will be | |
215 | called automatically before the underlying I2C bus itself is removed, as a | |
216 | device can't survive its parent in the device driver model. | |
217 | ||
218 | ||
4298cfc3 DB |
219 | Legacy Driver Binding Model |
220 | --------------------------- | |
221 | ||
1da177e4 LT |
222 | Most i2c devices can be present on several i2c addresses; for some this |
223 | is determined in hardware (by soldering some chip pins to Vcc or Ground), | |
224 | for others this can be changed in software (by writing to specific client | |
225 | registers). Some devices are usually on a specific address, but not always; | |
226 | and some are even more tricky. So you will probably need to scan several | |
227 | i2c addresses for your clients, and do some sort of detection to see | |
228 | whether it is actually a device supported by your driver. | |
229 | ||
230 | To give the user a maximum of possibilities, some default module parameters | |
231 | are defined to help determine what addresses are scanned. Several macros | |
232 | are defined in i2c.h to help you support them, as well as a generic | |
233 | detection algorithm. | |
234 | ||
235 | You do not have to use this parameter interface; but don't try to use | |
2ed2dc3c | 236 | function i2c_probe() if you don't. |
1da177e4 | 237 | |
1da177e4 | 238 | |
4298cfc3 DB |
239 | Probing classes (Legacy model) |
240 | ------------------------------ | |
1da177e4 LT |
241 | |
242 | All parameters are given as lists of unsigned 16-bit integers. Lists are | |
243 | terminated by I2C_CLIENT_END. | |
244 | The 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. | |
1da177e4 LT |
248 | 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. | |
1da177e4 LT |
252 | 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. | |
f4b50261 | 255 | This parameter overrules the 'normal_i2c' list only. |
1da177e4 LT |
256 | 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 | ||
f4b50261 JD |
261 | Additionally, kind-specific force lists may optionally be defined if |
262 | the driver supports several chip kinds. They are grouped in a | |
263 | NULL-terminated list of pointers named forces, those first element if the | |
264 | generic force list mentioned above. Each additional list correspond to an | |
265 | insmod parameter of the form force_<kind>. | |
266 | ||
b3d5496e JD |
267 | Fortunately, as a module writer, you just have to define the `normal_i2c' |
268 | parameter. The complete declaration could look like this: | |
1da177e4 | 269 | |
b3d5496e JD |
270 | /* Scan 0x37, and 0x48 to 0x4f */ |
271 | static unsigned short normal_i2c[] = { 0x37, 0x48, 0x49, 0x4a, 0x4b, 0x4c, | |
272 | 0x4d, 0x4e, 0x4f, I2C_CLIENT_END }; | |
1da177e4 LT |
273 | |
274 | /* Magic definition of all other variables and things */ | |
275 | I2C_CLIENT_INSMOD; | |
f4b50261 JD |
276 | /* Or, if your driver supports, say, 2 kind of devices: */ |
277 | I2C_CLIENT_INSMOD_2(foo, bar); | |
278 | ||
279 | If you use the multi-kind form, an enum will be defined for you: | |
280 | enum chips { any_chip, foo, bar, ... } | |
281 | You can then (and certainly should) use it in the driver code. | |
1da177e4 | 282 | |
b3d5496e JD |
283 | Note that you *have* to call the defined variable `normal_i2c', |
284 | without any prefix! | |
1da177e4 LT |
285 | |
286 | ||
4298cfc3 DB |
287 | Attaching to an adapter (Legacy model) |
288 | -------------------------------------- | |
1da177e4 LT |
289 | |
290 | Whenever a new adapter is inserted, or for all adapters if the driver is | |
291 | being registered, the callback attach_adapter() is called. Now is the | |
292 | time to determine what devices are present on the adapter, and to register | |
293 | a client for each of them. | |
294 | ||
295 | The attach_adapter callback is really easy: we just call the generic | |
296 | detection function. This function will scan the bus for us, using the | |
297 | information as defined in the lists explained above. If a device is | |
298 | detected 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 | ||
1da177e4 LT |
305 | Remember, structure `addr_data' is defined by the macros explained above, |
306 | so you do not have to define it yourself. | |
307 | ||
2ed2dc3c | 308 | The i2c_probe function will call the foo_detect_client |
1da177e4 LT |
309 | function only for those i2c addresses that actually have a device on |
310 | them (unless a `force' parameter was used). In addition, addresses that | |
311 | are already in use (by some other registered client) are skipped. | |
312 | ||
313 | ||
4298cfc3 DB |
314 | The detect client function (Legacy model) |
315 | ----------------------------------------- | |
1da177e4 | 316 | |
2ed2dc3c JD |
317 | The detect client function is called by i2c_probe. The `kind' parameter |
318 | contains -1 for a probed detection, 0 for a forced detection, or a positive | |
319 | number for a forced detection with a chip type forced. | |
1da177e4 | 320 | |
a89ba0bc JD |
321 | Returning an error different from -ENODEV in a detect function will cause |
322 | the detection to stop: other addresses and adapters won't be scanned. | |
323 | This should only be done on fatal or internal errors, such as a memory | |
324 | shortage or i2c_attach_client failing. | |
1da177e4 LT |
325 | |
326 | For 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, | |
eefcd75e | 329 | int kind) |
1da177e4 LT |
330 | { |
331 | int err = 0; | |
332 | int i; | |
eefcd75e | 333 | struct i2c_client *client; |
1da177e4 | 334 | struct foo_data *data; |
eefcd75e | 335 | const char *name = ""; |
1da177e4 LT |
336 | |
337 | /* Let's see whether this adapter can support what we need. | |
eefcd75e | 338 | Please substitute the things you need here! */ |
1da177e4 LT |
339 | if (!i2c_check_functionality(adapter,I2C_FUNC_SMBUS_WORD_DATA | |
340 | I2C_FUNC_SMBUS_WRITE_BYTE)) | |
341 | goto ERROR0; | |
342 | ||
1da177e4 LT |
343 | /* 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 | ||
2445eb62 | 347 | if (!(data = kzalloc(sizeof(struct foo_data), GFP_KERNEL))) { |
1da177e4 LT |
348 | err = -ENOMEM; |
349 | goto ERROR0; | |
350 | } | |
351 | ||
eefcd75e JD |
352 | client = &data->client; |
353 | i2c_set_clientdata(client, data); | |
1da177e4 | 354 | |
eefcd75e JD |
355 | client->addr = address; |
356 | client->adapter = adapter; | |
357 | client->driver = &foo_driver; | |
1da177e4 LT |
358 | |
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 */ | |
eefcd75e | 365 | if (foo_read(client, FOO_REG_GENERIC) != FOO_GENERIC_VALUE) |
1da177e4 LT |
366 | goto ERROR1; |
367 | } | |
368 | ||
1da177e4 LT |
369 | /* 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) { | |
eefcd75e | 375 | i = foo_read(client, FOO_REG_CHIPTYPE); |
1da177e4 LT |
376 | 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) { | |
eefcd75e | 389 | name = "chip1"; |
1da177e4 | 390 | } else if (kind == chip2) { |
eefcd75e | 391 | name = "chip2"; |
1da177e4 LT |
392 | } |
393 | ||
1da177e4 | 394 | /* Fill in the remaining client fields. */ |
eefcd75e | 395 | strlcpy(client->name, name, I2C_NAME_SIZE); |
1da177e4 | 396 | data->type = kind; |
eefcd75e | 397 | mutex_init(&data->update_lock); /* Only if you use this field */ |
1da177e4 LT |
398 | |
399 | /* Any other initializations in data must be done here too. */ | |
400 | ||
1da177e4 LT |
401 | /* This function can write default values to the client registers, if |
402 | needed. */ | |
eefcd75e JD |
403 | 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 | ||
1da177e4 LT |
409 | return 0; |
410 | ||
411 | /* OK, this is not exactly good programming practice, usually. But it is | |
412 | very code-efficient in this case. */ | |
413 | ||
1da177e4 | 414 | ERROR1: |
a852daa0 | 415 | kfree(data); |
1da177e4 LT |
416 | ERROR0: |
417 | return err; | |
418 | } | |
419 | ||
420 | ||
4298cfc3 DB |
421 | Removing the client (Legacy model) |
422 | ================================== | |
1da177e4 LT |
423 | |
424 | The detach_client call back function is called when a client should be | |
425 | removed. It may actually fail, but only when panicking. This code is | |
426 | much simpler than the attachment code, fortunately! | |
427 | ||
428 | int foo_detach_client(struct i2c_client *client) | |
429 | { | |
eefcd75e | 430 | int err; |
1da177e4 LT |
431 | |
432 | /* Try to detach the client from i2c space */ | |
7bef5594 | 433 | if ((err = i2c_detach_client(client))) |
1da177e4 | 434 | return err; |
1da177e4 | 435 | |
a852daa0 | 436 | kfree(i2c_get_clientdata(client)); |
1da177e4 LT |
437 | return 0; |
438 | } | |
439 | ||
440 | ||
441 | Initializing the module or kernel | |
442 | ================================= | |
443 | ||
444 | When the kernel is booted, or when your foo driver module is inserted, | |
445 | you have to do some initializing. Fortunately, just attaching (registering) | |
446 | the driver module is usually enough. | |
447 | ||
1da177e4 LT |
448 | static int __init foo_init(void) |
449 | { | |
450 | int res; | |
1da177e4 LT |
451 | |
452 | if ((res = i2c_add_driver(&foo_driver))) { | |
453 | printk("foo: Driver registration failed, module not inserted.\n"); | |
1da177e4 LT |
454 | return res; |
455 | } | |
1da177e4 LT |
456 | return 0; |
457 | } | |
458 | ||
eefcd75e | 459 | static void __exit foo_cleanup(void) |
1da177e4 | 460 | { |
eefcd75e | 461 | i2c_del_driver(&foo_driver); |
1da177e4 LT |
462 | } |
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 | ||
eefcd75e JD |
468 | /* a few non-GPL license types are also allowed */ |
469 | MODULE_LICENSE("GPL"); | |
470 | ||
1da177e4 LT |
471 | module_init(foo_init); |
472 | module_exit(foo_cleanup); | |
473 | ||
474 | Note that some functions are marked by `__init', and some data structures | |
eefcd75e | 475 | by `__initdata'. These functions and structures can be removed after |
1da177e4 LT |
476 | kernel booting (or module loading) is completed. |
477 | ||
fb687d73 | 478 | |
f37dd80a DB |
479 | Power Management |
480 | ================ | |
481 | ||
482 | If your I2C device needs special handling when entering a system low | |
483 | power state -- like putting a transceiver into a low power mode, or | |
484 | activating a system wakeup mechanism -- do that in the suspend() method. | |
485 | The resume() method should reverse what the suspend() method does. | |
486 | ||
487 | These are standard driver model calls, and they work just like they | |
488 | would for any other driver stack. The calls can sleep, and can use | |
489 | I2C messaging to the device being suspended or resumed (since their | |
490 | parent I2C adapter is active when these calls are issued, and IRQs | |
491 | are still enabled). | |
492 | ||
493 | ||
494 | System Shutdown | |
495 | =============== | |
496 | ||
497 | If your I2C device needs special handling when the system shuts down | |
498 | or reboots (including kexec) -- like turning something off -- use a | |
499 | shutdown() method. | |
500 | ||
501 | Again, this is a standard driver model call, working just like it | |
502 | would for any other driver stack: the calls can sleep, and can use | |
503 | I2C messaging. | |
504 | ||
505 | ||
1da177e4 LT |
506 | Command function |
507 | ================ | |
508 | ||
509 | A generic ioctl-like function call back is supported. You will seldom | |
fb687d73 JD |
510 | need this, and its use is deprecated anyway, so newer design should not |
511 | use it. Set it to NULL. | |
1da177e4 LT |
512 | |
513 | ||
514 | Sending and receiving | |
515 | ===================== | |
516 | ||
517 | If you want to communicate with your device, there are several functions | |
518 | to do this. You can find all of them in i2c.h. | |
519 | ||
520 | If you can choose between plain i2c communication and SMBus level | |
521 | communication, please use the last. All adapters understand SMBus level | |
522 | commands, but only some of them understand plain i2c! | |
523 | ||
524 | ||
525 | Plain 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 | ||
531 | These routines read and write some bytes from/to a client. The client | |
532 | contains the i2c address, so you do not have to include it. The second | |
533 | parameter contains the bytes the read/write, the third the length of the | |
534 | buffer. 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 | ||
539 | This sends a series of messages. Each message can be a read or write, | |
540 | and they can be mixed in any way. The transactions are combined: no | |
541 | stop bit is sent between transaction. The i2c_msg structure contains | |
542 | for each message the client address, the number of bytes of the message | |
543 | and the message data itself. | |
544 | ||
545 | You can read the file `i2c-protocol' for more information about the | |
546 | actual i2c protocol. | |
547 | ||
548 | ||
549 | SMBus 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); | |
7865e249 | 573 | extern s32 i2c_smbus_read_i2c_block_data(struct i2c_client * client, |
4b2643d7 | 574 | u8 command, u8 length, u8 *values); |
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575 | |
576 | These ones were removed in Linux 2.6.10 because they had no users, but could | |
577 | be added back later if needed: | |
578 | ||
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579 | 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 | ||
590 | All these transactions return -1 on failure. The 'write' transactions | |
591 | return 0 on success; the 'read' transactions return the read value, except | |
592 | for read_block, which returns the number of values read. The block buffers | |
593 | need not be longer than 32 bytes. | |
594 | ||
595 | You can read the file `smbus-protocol' for more information about the | |
596 | actual SMBus protocol. | |
597 | ||
598 | ||
599 | General purpose routines | |
600 | ======================== | |
601 | ||
602 | Below all general purpose routines are listed, that were not mentioned | |
603 | before. | |
604 | ||
eefcd75e | 605 | /* This call returns a unique low identifier for each registered adapter. |
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606 | */ |
607 | extern int i2c_adapter_id(struct i2c_adapter *adap); | |
608 |