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);
      strscpy(client->i2c_client.name, "example", sizeof(client->i2c_client.name));

      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 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;
-
-     strscpy(client->i2c_client.name, "example", sizeof(client->i2c_client.name));

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 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\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 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,
};