ep93xx SPI driver v3

[Martin Guy]

cc-ing to list...

> Next thing (after possible bug fixes, that is) is probably to
> implement proper DMA support. Unfortunately there is no platform
> code for that yet, only M2P controller support :( which means that
>  we have to implement M2M controller support

Yes, ep93xx DMA engine has two flavours: memory-to-peripheral, used
for most devices, and memory-to-memory, used for block memcpy and for
memory-to-SSP/SPI (== SD card).

The easiest route would seem to be to get the M2M stuff working to do
memcpy fast. Can linux make use of that? I haven't yet seen anything
that can make use of a memory-to-memory copy DMA engine.

If we can get that working, a reasonable second stage would make it
work for ep93xx-SPI transfers, making SD card access even less
CPU-intensive

   M