i2c: Documentation: upgrading clients HOWTO

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\n");

		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\n");

		kfree(state);

		return ret;

	}

	dev = &state->i2c_client.dev;

	/* rest of the initialisation goes here. */

	dev_info(dev, "example client created\n");

	return 0;

}

static int __devexit 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",

	},

	.attach_adapter = example_attach_adapter,

	.detach_client	= __devexit_p(example_detach),

	.suspend	= example_suspend,

	.resume		= example_resume,

};

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_adapter 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	= __devexit_p(example_detach),

 }

Add the probe and remove methods to the i2c_driver, as so:

 static struct i2c_driver example_driver = {

+	.probe		= example_probe,

+	.remove		= __devexit_p(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\n");

-		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\n");

		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 not needed for

any of the core functions.

- static int __devexit example_detach(struct i2c_client *client)

+ static int __devexit 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\n");

		return -ENOMEM;

	}

	state->client = client;

	i2c_set_clientdata(client, state);

	/* rest of the initialisation goes here. */

	dev_info(dev, "example client created\n");

	return 0;

}

static int __devexit 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",

	},

	.id_table	= example_idtable,

	.probe		= example_probe,

	.remove		= __devexit_p(example_remove),

	.suspend	= example_suspend,

	.resume		= example_resume,

};