I2C (pronounce: I-square-C) is a slow serial bus protocol used in
many micro controller applications and developed by Philips. SMBus,
or System Management Bus is a subset of the I2C protocol. More
information is contained in the directory Documentation/i2c/,
especially in the file called "summary" there.

Both I2C and SMBus are supported here. You will need this for
hardware sensors support, and also for Video For Linux support.

If you want I2C support, you should say Y here and also to the
specific driver for your bus adapter(s) below.

This I2C support can also be built as a module. If so, the module
will be called i2c-core.

source code:

drivers/i2c/i2c-core.c