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@@ -0,0 +1,281 @@
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+Upgrading I2C Drivers to the new 2.6 Driver Model
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+=================================================
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+
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+Ben Dooks <ben-linux@fluff.org>
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+
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+Introduction
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+------------
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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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+
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+
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+Example old-style driver
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+------------------------
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+
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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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+
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+static struct i2c_driver example_driver;
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+
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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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+
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+I2C_CLIENT_INSMOD;
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+
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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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+
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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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+
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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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+ i2c_set_clientdata(&state->i2c_client, state);
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+ strlcpy(client->i2c_client.name, "example", I2C_NAME_SIZE);
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+
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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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+
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+ dev = &state->i2c_client.dev;
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+
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+ /* rest of the initialisation goes here. */
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+
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+ dev_info(dev, "example client created\n");
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+
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+ return 0;
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+}
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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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+
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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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+
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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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+
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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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+
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+
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+Updating the client
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+-------------------
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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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+
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+- static struct i2c_driver example_driver;
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+
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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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+
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+- I2C_CLIENT_INSMOD;
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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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+
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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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+
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+Add the probe and remove methods to the i2c_driver, as so:
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+
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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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+
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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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+
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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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+
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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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+
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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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+
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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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+
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+The i2c_set_clientdata is now:
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+
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+- i2c_set_clientdata(&state->client, state);
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++ i2c_set_clientdata(client, state);
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+
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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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+
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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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+
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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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+
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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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+
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+the new i2c client as so:
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+
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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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+
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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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+
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+- dev = &state->i2c_client.dev;
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+
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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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+
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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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+
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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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+
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++ state->client = i2c_client;
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+
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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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+
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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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+
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+- i2c_detach_client(client);
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+
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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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+
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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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+
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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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+
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+
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+Our driver should now look like this:
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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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+
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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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+
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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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+
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+ state->client = client;
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+ i2c_set_clientdata(client, state);
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+
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+ /* rest of the initialisation goes here. */
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+
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+ dev_info(dev, "example client created\n");
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+
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+ return 0;
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+}
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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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+
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+ kfree(state);
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+ return 0;
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+}
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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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+
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+MODULE_DEVICE_TABLE(i2c, example_idtable);
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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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+ .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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Linus Torvalds