[Balloon] SPI - reasonable candidate for expansion stuff?

Hi, all.
SPI seems to be a reasonable local bus for future stuff. Low pin count,
reasonable bitrate, a fair and growing number of SDIO peripherals, and SD
cards are a reasonable way of adding storage.
The EP9302 on Airship only supports the one-bit SDIO interface, but
PXA27x on Balloon3 has the full thing.
Using SPI as the link between the propellor(s) on Airship and the EP9302
has charm - the propellor can be the master, which will allow us to run
the bus as hard as possible (since propellor has no hardware SPI, it ought
to generate the clock).
Is there support in the Linux flavours we're tending to use for SD and
SDIO stuff?

Steve