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UM0851

Communication device drivers

Doc ID 16604 Rev 2

83/245

This function is responsible for creating a struct i2c_client structure that will be registered

with the I2C core. The I2C core uses that structure as an individual I2C chip device. To

create this structure, the eeprom_detect() function is used:

struct i2c_client *new_client;

struct eeprom_data *data;

int err = 0;

if (!(data = kzalloc(sizeof(struct eeprom_data), GFP_KERNEL))) {

err = -ENOMEM;

goto exit;

}

new_client = &data->client;

memset(data->data, 0xff, EEPROM_SIZE);

i2c_set_clientdata(new_client, data);

new_client->addr = address;

new_client->adapter = adapter;

new_client->driver = &eeprom_driver;

new_client->flags = 0;

strlcpy(new_client->name, "eeprom", I2C_NAME_SIZE);

First, the struct i2c_client and a separate local data structure (called struct eeprom_data)

are created. After the memory is allocated successfully, some fields in the struct i2c_client

are set to point to this specific device and this specific driver. Notably, the addr, adapter and

driver variables must be initialized. The name of the struct i2c_client also must be set in

order to be displayed properly in the sysfs tree for this I2C device.

After the struct i2c_client is initialized, it must be registered with the I2C core. This is done

with a call to the i2c_attach_client() function

/* Tell the I2C layer a new client has arrived */

if ((err = i2c_attach_client(new_client)))

goto exit_kfree;

When this function returns, with no errors reported, the I2C chip device is set up properly in

the kernel.

For creating sysfs tree structure

sysfs_create_bin_file(&new_client->dev.kobj, &eeprom_attr);

In the Linux 2.6 kernel, all I2C chip devices and adapters show up in the sysfs filesystem.

I2C chip devices can be found at /sys/bus/i2c/devices, listed by their adapter address and

chip address. For example, the eeprom_driver loaded on a machine might produce the

following sysfs tree structure.

$ tree /sys/bus/i2c/

/sys/bus/i2c/

|-- devices

|-- 0-0050 ->../../devices/platform/spear_i2c.6/i2c-0/0-0050

|-- 0-0051 -> ../../../devices/platform/spear_i2c.6/i2c-0/0-0051

|-- 0-0052 -> ../../../devices/platform/spear_i2c.6/i2c-0/0-0052

`-- 0-0053 -> ../../../devices/platform/spear_i2c.6/i2c-0/0-0053

`-- drivers

|-- i2c_adapter

`-- eeprom

|-- 0-0050 -> ../../../devices/platform/spear_i2c.6/i2c-0/0-0050

|-- 0-0051 -> ../../../devices/platform/spear_i2c.6/i2c-0/0-0051

|-- 0-0052 -> ../../../devices/platform/spear_i2c.6/i2c-0/0-0052

`-- 0-0053 -> ../../../devices/platform/spear_i2c.6/i2c-0/0-0053

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