When working with the tivaware lib, you need two functions to configure the GPIOs to work with a given peripheral:
GPIOPinConfigure() and GPIOPinTypeXXX()
Now the discription of those functions where i little confusing (at least to me) so here is my explanation of how they work:
GPIOPinConfigure() and GPIOPinTypeXXX() are two parts of the same thing.
GPIOPinConfigure() configures the pin mux that selects the peripheral function
associated with a particular GPIO pin. ONLY AFFECTS THE MUX AND NOTHING MORE.
GPIOPinTypeXXX() on the other hand, configures the GPIO pins with the needed config
for the intended peripheral. For example if it was the I2C peripheral, the GPIOPinTypeI2C()
would configure the pins with internal pull-ups for the sda and sca lines and connect
the external pins to the I2C peripheral.