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Based on kernel version 4.1. Page generated on 2015-06-28 12:13 EST.

1	Upgrading I2C Drivers to the new 2.6 Driver Model
2	=================================================
3	
4	Ben Dooks <ben-linux@fluff.org>
5	
6	Introduction
7	------------
8	
9	This guide outlines how to alter existing Linux 2.6 client drivers from
10	the old to the new new binding methods.
11	
12	
13	Example old-style driver
14	------------------------
15	
16	
17	struct example_state {
18		struct i2c_client	client;
19		....
20	};
21	
22	static struct i2c_driver example_driver;
23	
24	static unsigned short ignore[] = { I2C_CLIENT_END };
25	static unsigned short normal_addr[] = { OUR_ADDR, I2C_CLIENT_END };
26	
27	I2C_CLIENT_INSMOD;
28	
29	static 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	
64	static 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	
73	static int example_attach_adapter(struct i2c_adapter *adap)
74	{
75		return i2c_probe(adap, &addr_data, example_attach);
76	}
77	
78	static 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	
89	Updating the client
90	-------------------
91	
92	The new style binding model will check against a list of supported
93	devices and their associated address supplied by the code registering
94	the busses. This means that the driver .attach_adapter and
95	.detach_client methods can be removed, along with the addr_data,
96	as 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	
115	Add 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	
122	Change the example_attach method to accept the new parameters
123	which 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	
129	Change the name of example_attach to example_probe to align it with the
130	i2c_driver entry names. The rest of the probe routine will now need to be
131	changed as the i2c_client has already been setup for use.
132	
133	The necessary client fields have already been setup before
134	the probe function is called, so the following client setup
135	can 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	
143	The i2c_set_clientdata is now:
144	
145	-	i2c_set_clientdata(&state->client, state);
146	+	i2c_set_clientdata(client, state);
147	
148	The call to i2c_attach_client is no longer needed, if the probe
149	routine exits successfully, then the driver will be automatically
150	attached 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	
160	Remove the storage of 'struct i2c_client' from the 'struct example_state'
161	as we are provided with the i2c_client in our example_probe. Instead we
162	store a pointer to it for when it is needed.
163	
164	struct example_state {
165	-	struct i2c_client	client;
166	+	struct i2c_client	*client;
167	
168	the 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	
173	And remove the change after our client is attached, as the driver no
174	longer needs to register a new client structure with the core:
175	
176	-	dev = &state->i2c_client.dev;
177	
178	In the probe routine, ensure that the new state has the client stored
179	in it:
180	
181	static 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	
196	Update the detach method, by changing the name to _remove and
197	to delete the i2c_detach_client call. It is possible that you
198	can also remove the ret variable as it is not needed for any
199	of 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	
208	And finally ensure that we have the correct ID table for the i2c-core
209	and other utilities:
210	
211	+ struct i2c_device_id example_idtable[] = {
212	+       { "example", 0 },
213	+       { }
214	+};
215	+
216	+MODULE_DEVICE_TABLE(i2c, example_idtable);
217	
218	static struct i2c_driver example_driver = {
219	 	.driver		= {
220			.owner		= THIS_MODULE,
221			.name		= "example",
222		},
223	+	.id_table	= example_ids,
224	
225	
226	Our driver should now look like this:
227	
228	struct example_state {
229		struct i2c_client	*client;
230		....
231	};
232	
233	static 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	
255	static 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	
263	static struct i2c_device_id example_idtable[] = {
264		{ "example", 0 },
265		{ }
266	};
267	
268	MODULE_DEVICE_TABLE(i2c, example_idtable);
269	
270	static 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	};
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