1Upgrading I2C Drivers to the new 2.6 Driver Model
  2=================================================
  3
  4Ben Dooks <ben-linux@fluff.org>
  5
  6Introduction
  7------------
  8
  9This guide outlines how to alter existing Linux 2.6 client drivers from
 10the old to the new new binding methods.
 11
 12
 13Example old-style driver
 14------------------------
 15
 16
 17struct example_state {
 18	struct i2c_client	client;
 19	....
 20};
 21
 22static struct i2c_driver example_driver;
 23
 24static unsigned short ignore[] = { I2C_CLIENT_END };
 25static unsigned short normal_addr[] = { OUR_ADDR, I2C_CLIENT_END };
 26
 27I2C_CLIENT_INSMOD;
 28
 29static int example_attach(struct i2c_adapter *adap, int addr, int kind)
 30{
 31	struct example_state *state;
 32	struct device *dev = &adap->dev;  /* to use for dev_ reports */
 33	int ret;
 34
 35	state = kzalloc(sizeof(struct example_state), GFP_KERNEL);
 36	if (state == NULL) {
 37		dev_err(dev, "failed to create our state\n");
 38		return -ENOMEM;
 39	}
 40
 41	example->client.addr    = addr;
 42	example->client.flags   = 0;
 43	example->client.adapter = adap;
 44
 45	i2c_set_clientdata(&state->i2c_client, state);
 46	strlcpy(client->i2c_client.name, "example", I2C_NAME_SIZE);
 47
 48	ret = i2c_attach_client(&state->i2c_client);
 49	if (ret < 0) {
 50		dev_err(dev, "failed to attach client\n");
 51		kfree(state);
 52		return ret;
 53	}
 54
 55	dev = &state->i2c_client.dev;
 56
 57	/* rest of the initialisation goes here. */
 58
 59	dev_info(dev, "example client created\n");
 60
 61	return 0;
 62}
 63
 64static int example_detach(struct i2c_client *client)
 65{
 66	struct example_state *state = i2c_get_clientdata(client);
 67
 68	i2c_detach_client(client);
 69	kfree(state);
 70	return 0;
 71}
 72
 73static int example_attach_adapter(struct i2c_adapter *adap)
 74{
 75	return i2c_probe(adap, &addr_data, example_attach);
 76}
 77
 78static struct i2c_driver example_driver = {
 79 	.driver		= {
 80		.owner		= THIS_MODULE,
 81		.name		= "example",
 82		.pm		= &example_pm_ops,
 83	},
 84	.attach_adapter = example_attach_adapter,
 85	.detach_client	= example_detach,
 86};
 87
 88
 89Updating the client
 90-------------------
 91
 92The new style binding model will check against a list of supported
 93devices and their associated address supplied by the code registering
 94the busses. This means that the driver .attach_adapter and
 95.detach_client methods can be removed, along with the addr_data,
 96as follows:
 97
 98- static struct i2c_driver example_driver;
 99
100- static unsigned short ignore[] = { I2C_CLIENT_END };
101- static unsigned short normal_addr[] = { OUR_ADDR, I2C_CLIENT_END };
102
103- I2C_CLIENT_INSMOD;
104
105- static int example_attach_adapter(struct i2c_adapter *adap)
106- {
107- 	return i2c_probe(adap, &addr_data, example_attach);
108- }
109
110 static struct i2c_driver example_driver = {
111-	.attach_adapter = example_attach_adapter,
112-	.detach_client	= example_detach,
113 }
114
115Add the probe and remove methods to the i2c_driver, as so:
116
117 static struct i2c_driver example_driver = {
118+	.probe		= example_probe,
119+	.remove		= example_remove,
120 }
121
122Change the example_attach method to accept the new parameters
123which include the i2c_client that it will be working with:
124
125- static int example_attach(struct i2c_adapter *adap, int addr, int kind)
126+ static int example_probe(struct i2c_client *client,
127+			   const struct i2c_device_id *id)
128
129Change the name of example_attach to example_probe to align it with the
130i2c_driver entry names. The rest of the probe routine will now need to be
131changed as the i2c_client has already been setup for use.
132
133The necessary client fields have already been setup before
134the probe function is called, so the following client setup
135can be removed:
136
137-	example->client.addr    = addr;
138-	example->client.flags   = 0;
139-	example->client.adapter = adap;
140-
141-	strlcpy(client->i2c_client.name, "example", I2C_NAME_SIZE);
142
143The i2c_set_clientdata is now:
144
145-	i2c_set_clientdata(&state->client, state);
146+	i2c_set_clientdata(client, state);
147
148The call to i2c_attach_client is no longer needed, if the probe
149routine exits successfully, then the driver will be automatically
150attached by the core. Change the probe routine as so:
151
152-	ret = i2c_attach_client(&state->i2c_client);
153-	if (ret < 0) {
154-		dev_err(dev, "failed to attach client\n");
155-		kfree(state);
156-		return ret;
157-	}
158
159
160Remove the storage of 'struct i2c_client' from the 'struct example_state'
161as we are provided with the i2c_client in our example_probe. Instead we
162store a pointer to it for when it is needed.
163
164struct example_state {
165-	struct i2c_client	client;
166+	struct i2c_client	*client;
167
168the new i2c client as so:
169
170-	struct device *dev = &adap->dev;  /* to use for dev_ reports */
171+ 	struct device *dev = &i2c_client->dev;  /* to use for dev_ reports */
172
173And remove the change after our client is attached, as the driver no
174longer needs to register a new client structure with the core:
175
176-	dev = &state->i2c_client.dev;
177
178In the probe routine, ensure that the new state has the client stored
179in it:
180
181static int example_probe(struct i2c_client *i2c_client,
182			 const struct i2c_device_id *id)
183{
184	struct example_state *state;
185 	struct device *dev = &i2c_client->dev;
186	int ret;
187
188	state = kzalloc(sizeof(struct example_state), GFP_KERNEL);
189	if (state == NULL) {
190		dev_err(dev, "failed to create our state\n");
191		return -ENOMEM;
192	}
193
194+	state->client = i2c_client;
195
196Update the detach method, by changing the name to _remove and
197to delete the i2c_detach_client call. It is possible that you
198can also remove the ret variable as it is not needed for any
199of the core functions.
200
201- static int example_detach(struct i2c_client *client)
202+ static int example_remove(struct i2c_client *client)
203{
204	struct example_state *state = i2c_get_clientdata(client);
205
206-	i2c_detach_client(client);
207
208And finally ensure that we have the correct ID table for the i2c-core
209and other utilities:
210
211+ struct i2c_device_id example_idtable[] = {
212+       { "example", 0 },
213+       { }
214+};
215+
216+MODULE_DEVICE_TABLE(i2c, example_idtable);
217
218static struct i2c_driver example_driver = {
219 	.driver		= {
220		.owner		= THIS_MODULE,
221		.name		= "example",
222	},
223+	.id_table	= example_ids,
224
225
226Our driver should now look like this:
227
228struct example_state {
229	struct i2c_client	*client;
230	....
231};
232
233static int example_probe(struct i2c_client *client,
234		     	 const struct i2c_device_id *id)
235{
236	struct example_state *state;
237	struct device *dev = &client->dev;
238
239	state = kzalloc(sizeof(struct example_state), GFP_KERNEL);
240	if (state == NULL) {
241		dev_err(dev, "failed to create our state\n");
242		return -ENOMEM;
243	}
244
245	state->client = client;
246	i2c_set_clientdata(client, state);
247
248	/* rest of the initialisation goes here. */
249
250	dev_info(dev, "example client created\n");
251
252	return 0;
253}
254
255static int example_remove(struct i2c_client *client)
256{
257	struct example_state *state = i2c_get_clientdata(client);
258
259	kfree(state);
260	return 0;
261}
262
263static struct i2c_device_id example_idtable[] = {
264	{ "example", 0 },
265	{ }
266};
267
268MODULE_DEVICE_TABLE(i2c, example_idtable);
269
270static struct i2c_driver example_driver = {
271 	.driver		= {
272		.owner		= THIS_MODULE,
273		.name		= "example",
274		.pm		= &example_pm_ops,
275	},
276	.id_table	= example_idtable,
277	.probe		= example_probe,
278	.remove		= example_remove,
279};