The device driver for the XO's Marvell 88W8386 USB wireless SoC is known as Libertas Driver.
The driver is licensed under GPL but requires a non-FOSS firmware to operate.
Though the Libertas driver is currently part of the mainline Linux Kernel, OLPC keeps a development version that addresses its specific needs and adds new features that are still not mainline. The OLPC version can be browsed in this web interface to the OLPC's git tree.
Libertas ThinFirm Driver
Knobs and User Control
Most of what can done (from user space) in terms of adjusting the behavior of the wireless subsystem is documented in the Libertas Driver README.