i2c4 disabled in kernel


does anybody know why i2c4 disabled in kernel? Specifically I try to bring up 3.7x to my device and found that the function omap_register_i2c_bus() hangs when the bus number is 4. Digging into code shows that this check is true
BUG_ON(bus_id < 1 || bus_id > omap_i2c_nr_ports());

because omap_i2c_nr_ports() returns 3.

any comments are appreciated