libertas_spi, is available in wireless-testing and coming to a future kernel (2.6.30, most likely).
GSPI is very easy to interface as it consists of a normal SPI bus, an IRQ line, and one GPIO line that acts as a chip select signal (as such, be sure to enable
CONFIG_GENERIC_GPIOin your kernel config in order to build the new
libertas_spidriver). The GPIO-style chip select is different from a typical SPI chip select in that the chip select stays asserted for an arbitrary number of SPI bus transactions.