Upgrading I2C Drivers to the new 2.6 Driver Model
  =================================================
  
  Ben Dooks <ben-linux@fluff.org>
  
  Introduction
  ------------
  
  This guide outlines how to alter existing Linux 2.6 client drivers from
  the old to the new new binding methods.
  
  
  Example old-style driver
  ------------------------
  
  
  struct example_state {
  	struct i2c_client	client;
  	....
  };
  
  static struct i2c_driver example_driver;
  
  static unsigned short ignore[] = { I2C_CLIENT_END };
  static unsigned short normal_addr[] = { OUR_ADDR, I2C_CLIENT_END };
  
  I2C_CLIENT_INSMOD;
  
  static int example_attach(struct i2c_adapter *adap, int addr, int kind)
  {
  	struct example_state *state;
  	struct device *dev = &adap->dev;  /* to use for dev_ reports */
  	int ret;
  
  	state = kzalloc(sizeof(struct example_state), GFP_KERNEL);
  	if (state == NULL) {
  		dev_err(dev, "failed to create our state
  ");
  		return -ENOMEM;
  	}
  
  	example->client.addr    = addr;
  	example->client.flags   = 0;
  	example->client.adapter = adap;
  
  	i2c_set_clientdata(&state->i2c_client, state);
  	strlcpy(client->i2c_client.name, "example", I2C_NAME_SIZE);
  
  	ret = i2c_attach_client(&state->i2c_client);
  	if (ret < 0) {
  		dev_err(dev, "failed to attach client
  ");
  		kfree(state);
  		return ret;
  	}
  
  	dev = &state->i2c_client.dev;
  
  	/* rest of the initialisation goes here. */
  
  	dev_info(dev, "example client created
  ");
  
  	return 0;
  }

  static int example_detach(struct i2c_client *client)

  {
  	struct example_state *state = i2c_get_clientdata(client);
  
  	i2c_detach_client(client);
  	kfree(state);
  	return 0;
  }
  
  static int example_attach_adapter(struct i2c_adapter *adap)
  {
  	return i2c_probe(adap, &addr_data, example_attach);
  }
  
  static struct i2c_driver example_driver = {
   	.driver		= {
  		.owner		= THIS_MODULE,
  		.name		= "example",

  		.pm		= &example_pm_ops,

  	},
  	.attach_adapter = example_attach_adapter,

  	.detach_client	= example_detach,

  };
  
  
  Updating the client
  -------------------
  
  The new style binding model will check against a list of supported
  devices and their associated address supplied by the code registering
  the busses. This means that the driver .attach_adapter and

  .detach_client methods can be removed, along with the addr_data,

  as follows:
  
  - static struct i2c_driver example_driver;
  
  - static unsigned short ignore[] = { I2C_CLIENT_END };
  - static unsigned short normal_addr[] = { OUR_ADDR, I2C_CLIENT_END };
  
  - I2C_CLIENT_INSMOD;
  
  - static int example_attach_adapter(struct i2c_adapter *adap)
  - {
  - 	return i2c_probe(adap, &addr_data, example_attach);
  - }
  
   static struct i2c_driver example_driver = {
  -	.attach_adapter = example_attach_adapter,

  -	.detach_client	= example_detach,

   }
  
  Add the probe and remove methods to the i2c_driver, as so:
  
   static struct i2c_driver example_driver = {
  +	.probe		= example_probe,

  +	.remove		= example_remove,

   }
  
  Change the example_attach method to accept the new parameters
  which include the i2c_client that it will be working with:
  
  - static int example_attach(struct i2c_adapter *adap, int addr, int kind)
  + static int example_probe(struct i2c_client *client,
  +			   const struct i2c_device_id *id)
  
  Change the name of example_attach to example_probe to align it with the
  i2c_driver entry names. The rest of the probe routine will now need to be
  changed as the i2c_client has already been setup for use.
  
  The necessary client fields have already been setup before
  the probe function is called, so the following client setup
  can be removed:
  
  -	example->client.addr    = addr;
  -	example->client.flags   = 0;
  -	example->client.adapter = adap;
  -
  -	strlcpy(client->i2c_client.name, "example", I2C_NAME_SIZE);
  
  The i2c_set_clientdata is now:
  
  -	i2c_set_clientdata(&state->client, state);
  +	i2c_set_clientdata(client, state);
  
  The call to i2c_attach_client is no longer needed, if the probe
  routine exits successfully, then the driver will be automatically
  attached by the core. Change the probe routine as so:
  
  -	ret = i2c_attach_client(&state->i2c_client);
  -	if (ret < 0) {
  -		dev_err(dev, "failed to attach client
  ");
  -		kfree(state);
  -		return ret;
  -	}
  
  
  Remove the storage of 'struct i2c_client' from the 'struct example_state'
  as we are provided with the i2c_client in our example_probe. Instead we
  store a pointer to it for when it is needed.
  
  struct example_state {
  -	struct i2c_client	client;
  +	struct i2c_client	*client;
  
  the new i2c client as so:
  
  -	struct device *dev = &adap->dev;  /* to use for dev_ reports */
  + 	struct device *dev = &i2c_client->dev;  /* to use for dev_ reports */
  
  And remove the change after our client is attached, as the driver no
  longer needs to register a new client structure with the core:
  
  -	dev = &state->i2c_client.dev;
  
  In the probe routine, ensure that the new state has the client stored
  in it:
  
  static int example_probe(struct i2c_client *i2c_client,
  			 const struct i2c_device_id *id)
  {
  	struct example_state *state;
   	struct device *dev = &i2c_client->dev;
  	int ret;
  
  	state = kzalloc(sizeof(struct example_state), GFP_KERNEL);
  	if (state == NULL) {
  		dev_err(dev, "failed to create our state
  ");
  		return -ENOMEM;
  	}
  
  +	state->client = i2c_client;
  
  Update the detach method, by changing the name to _remove and
  to delete the i2c_detach_client call. It is possible that you

  can also remove the ret variable as it is not needed for any
  of the core functions.

  - static int example_detach(struct i2c_client *client)
  + static int example_remove(struct i2c_client *client)

  {
  	struct example_state *state = i2c_get_clientdata(client);
  
  -	i2c_detach_client(client);
  
  And finally ensure that we have the correct ID table for the i2c-core
  and other utilities:
  
  + struct i2c_device_id example_idtable[] = {
  +       { "example", 0 },
  +       { }
  +};
  +
  +MODULE_DEVICE_TABLE(i2c, example_idtable);
  
  static struct i2c_driver example_driver = {
   	.driver		= {
  		.owner		= THIS_MODULE,
  		.name		= "example",
  	},
  +	.id_table	= example_ids,
  
  
  Our driver should now look like this:
  
  struct example_state {
  	struct i2c_client	*client;
  	....
  };
  
  static int example_probe(struct i2c_client *client,
  		     	 const struct i2c_device_id *id)
  {
  	struct example_state *state;
  	struct device *dev = &client->dev;
  
  	state = kzalloc(sizeof(struct example_state), GFP_KERNEL);
  	if (state == NULL) {
  		dev_err(dev, "failed to create our state
  ");
  		return -ENOMEM;
  	}
  
  	state->client = client;
  	i2c_set_clientdata(client, state);
  
  	/* rest of the initialisation goes here. */
  
  	dev_info(dev, "example client created
  ");
  
  	return 0;
  }

  static int example_remove(struct i2c_client *client)

  {
  	struct example_state *state = i2c_get_clientdata(client);
  
  	kfree(state);
  	return 0;
  }
  
  static struct i2c_device_id example_idtable[] = {
  	{ "example", 0 },
  	{ }
  };
  
  MODULE_DEVICE_TABLE(i2c, example_idtable);
  
  static struct i2c_driver example_driver = {
   	.driver		= {
  		.owner		= THIS_MODULE,
  		.name		= "example",

  		.pm		= &example_pm_ops,

  	},
  	.id_table	= example_idtable,
  	.probe		= example_probe,

  	.remove		= example_remove,

  };