The I2C bus in Linux

Each I²C device has a well defined 7 bits address that the master must use in order to communicate with a device. This address is not assigned at runtime as for the USB devices, it's assigned by the board designer by setting some chip's pins.

Note

Typically the chip manufacturer set most significant 3 or 4 bits and the board designer can set remaining bits in order to suite his/her needs. I²C bus specifications are controlled by NXP (Philips) and they are the ones who allocate addresses to I²C devices.

Another thing to be outlined regarding the I²C bus is that for each message the master must specify if the message wants read or write data from the slave. This special action is done by adding a final bit (least significant bit) to the slave address, the master uses a 0 to write data and a 1 to read data from the slave.

As for the USB bus we still have two main actors: master and slave. So in the kernel we find both the device driver types.

Regarding I²C master device there...