The PXA270 SD controller has a hardware bug where it cannot handle 2 or 3 byte sd cmds. Depending on the version of the AR6K driver you are using, there may be define in hif.c that forces short transfers to 4-byte. FYI - this is not as simple as just padding.
Paul.
2009-01-15 19:36:09 UTC in Linux SDIO stack project