i2c: Documentation: upgrading clients HOWTO
Add a document describing how i2c clients on Linux 2.6 can be moved from the old to the new driver model. Signed-off-by: Ben Dooks <ben-linux@fluff.org>
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Documentation/i2c/upgrading-clients
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Documentation/i2c/upgrading-clients
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Upgrading I2C Drivers to the new 2.6 Driver Model
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=================================================
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Ben Dooks <ben-linux@fluff.org>
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Introduction
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------------
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This guide outlines how to alter existing Linux 2.6 client drivers from
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the old to the new new binding methods.
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Example old-style driver
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------------------------
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struct example_state {
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struct i2c_client client;
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....
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};
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static struct i2c_driver example_driver;
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static unsigned short ignore[] = { I2C_CLIENT_END };
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static unsigned short normal_addr[] = { OUR_ADDR, I2C_CLIENT_END };
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I2C_CLIENT_INSMOD;
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static int example_attach(struct i2c_adapter *adap, int addr, int kind)
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{
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struct example_state *state;
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struct device *dev = &adap->dev; /* to use for dev_ reports */
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int ret;
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state = kzalloc(sizeof(struct example_state), GFP_KERNEL);
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if (state == NULL) {
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dev_err(dev, "failed to create our state\n");
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return -ENOMEM;
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}
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example->client.addr = addr;
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example->client.flags = 0;
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example->client.adapter = adap;
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i2c_set_clientdata(&state->i2c_client, state);
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strlcpy(client->i2c_client.name, "example", I2C_NAME_SIZE);
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ret = i2c_attach_client(&state->i2c_client);
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if (ret < 0) {
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dev_err(dev, "failed to attach client\n");
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kfree(state);
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return ret;
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}
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dev = &state->i2c_client.dev;
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/* rest of the initialisation goes here. */
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dev_info(dev, "example client created\n");
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return 0;
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}
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static int __devexit example_detach(struct i2c_client *client)
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{
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struct example_state *state = i2c_get_clientdata(client);
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i2c_detach_client(client);
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kfree(state);
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return 0;
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}
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static int example_attach_adapter(struct i2c_adapter *adap)
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{
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return i2c_probe(adap, &addr_data, example_attach);
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}
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static struct i2c_driver example_driver = {
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.driver = {
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.owner = THIS_MODULE,
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.name = "example",
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},
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.attach_adapter = example_attach_adapter,
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.detach_client = __devexit_p(example_detach),
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.suspend = example_suspend,
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.resume = example_resume,
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};
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Updating the client
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-------------------
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The new style binding model will check against a list of supported
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devices and their associated address supplied by the code registering
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the busses. This means that the driver .attach_adapter and
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.detach_adapter methods can be removed, along with the addr_data,
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as follows:
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- static struct i2c_driver example_driver;
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- static unsigned short ignore[] = { I2C_CLIENT_END };
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- static unsigned short normal_addr[] = { OUR_ADDR, I2C_CLIENT_END };
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- I2C_CLIENT_INSMOD;
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- static int example_attach_adapter(struct i2c_adapter *adap)
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- {
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- return i2c_probe(adap, &addr_data, example_attach);
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- }
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static struct i2c_driver example_driver = {
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- .attach_adapter = example_attach_adapter,
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- .detach_client = __devexit_p(example_detach),
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}
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Add the probe and remove methods to the i2c_driver, as so:
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static struct i2c_driver example_driver = {
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+ .probe = example_probe,
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+ .remove = __devexit_p(example_remove),
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}
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Change the example_attach method to accept the new parameters
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which include the i2c_client that it will be working with:
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- static int example_attach(struct i2c_adapter *adap, int addr, int kind)
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+ static int example_probe(struct i2c_client *client,
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+ const struct i2c_device_id *id)
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Change the name of example_attach to example_probe to align it with the
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i2c_driver entry names. The rest of the probe routine will now need to be
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changed as the i2c_client has already been setup for use.
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The necessary client fields have already been setup before
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the probe function is called, so the following client setup
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can be removed:
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- example->client.addr = addr;
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- example->client.flags = 0;
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- example->client.adapter = adap;
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-
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- strlcpy(client->i2c_client.name, "example", I2C_NAME_SIZE);
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The i2c_set_clientdata is now:
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- i2c_set_clientdata(&state->client, state);
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+ i2c_set_clientdata(client, state);
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The call to i2c_attach_client is no longer needed, if the probe
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routine exits successfully, then the driver will be automatically
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attached by the core. Change the probe routine as so:
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- ret = i2c_attach_client(&state->i2c_client);
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- if (ret < 0) {
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- dev_err(dev, "failed to attach client\n");
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- kfree(state);
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- return ret;
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- }
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Remove the storage of 'struct i2c_client' from the 'struct example_state'
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as we are provided with the i2c_client in our example_probe. Instead we
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store a pointer to it for when it is needed.
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struct example_state {
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- struct i2c_client client;
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+ struct i2c_client *client;
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the new i2c client as so:
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- struct device *dev = &adap->dev; /* to use for dev_ reports */
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+ struct device *dev = &i2c_client->dev; /* to use for dev_ reports */
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And remove the change after our client is attached, as the driver no
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longer needs to register a new client structure with the core:
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- dev = &state->i2c_client.dev;
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In the probe routine, ensure that the new state has the client stored
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in it:
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static int example_probe(struct i2c_client *i2c_client,
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const struct i2c_device_id *id)
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{
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struct example_state *state;
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struct device *dev = &i2c_client->dev;
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int ret;
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state = kzalloc(sizeof(struct example_state), GFP_KERNEL);
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if (state == NULL) {
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dev_err(dev, "failed to create our state\n");
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return -ENOMEM;
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}
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+ state->client = i2c_client;
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Update the detach method, by changing the name to _remove and
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to delete the i2c_detach_client call. It is possible that you
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can also remove the ret variable as it is not not needed for
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any of the core functions.
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- static int __devexit example_detach(struct i2c_client *client)
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+ static int __devexit example_remove(struct i2c_client *client)
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{
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struct example_state *state = i2c_get_clientdata(client);
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- i2c_detach_client(client);
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And finally ensure that we have the correct ID table for the i2c-core
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and other utilities:
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+ struct i2c_device_id example_idtable[] = {
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+ { "example", 0 },
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+ { }
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+};
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+
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+MODULE_DEVICE_TABLE(i2c, example_idtable);
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static struct i2c_driver example_driver = {
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.driver = {
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.owner = THIS_MODULE,
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.name = "example",
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},
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+ .id_table = example_ids,
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Our driver should now look like this:
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struct example_state {
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struct i2c_client *client;
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....
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};
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static int example_probe(struct i2c_client *client,
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const struct i2c_device_id *id)
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{
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struct example_state *state;
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struct device *dev = &client->dev;
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state = kzalloc(sizeof(struct example_state), GFP_KERNEL);
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if (state == NULL) {
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dev_err(dev, "failed to create our state\n");
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return -ENOMEM;
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}
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state->client = client;
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i2c_set_clientdata(client, state);
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/* rest of the initialisation goes here. */
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dev_info(dev, "example client created\n");
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return 0;
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}
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static int __devexit example_remove(struct i2c_client *client)
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{
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struct example_state *state = i2c_get_clientdata(client);
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kfree(state);
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return 0;
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}
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static struct i2c_device_id example_idtable[] = {
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{ "example", 0 },
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{ }
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};
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MODULE_DEVICE_TABLE(i2c, example_idtable);
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static struct i2c_driver example_driver = {
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.driver = {
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.owner = THIS_MODULE,
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.name = "example",
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},
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.id_table = example_idtable,
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.probe = example_probe,
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.remove = __devexit_p(example_remove),
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.suspend = example_suspend,
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.resume = example_resume,
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};
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