Hi Lee,
The McSPI driver is freely available. Just download the latest Sitara AM335x SDK from here: http://software-dl.ti.com/sitara_linux/esd/AM335xSDK/latest/index_FDS.html
The McSPI driver is located in: <sdk_dir>/drivers/spi/spi-omap2-mcspi.c
I don't really know how well the driver has been optimized and if there is any room for improvement, but this comment in the code makes me believe it is:
[quote]/* use PIO for small transfers, avoiding DMA setup/teardown overhead and
* cache operations; better heuristics consider wordsize and bitrate.
*/
#define DMA_MIN_BYTES 160[/quote]
Best regards,
Miroslav