The MMCplus Application note (version 4): http://www.mmca.org/compliance/buy_s...MMCA050419.pdf says:

"The initialization procedure of MMCplus is equivalent to that of cards by standard version 3.31. The major difference is that any dedicated MMCplus host application is restriced to have only a single card slot (in order to cope with the increased frequency requirements)."

However it looks like standard MMC might be ok. Does anyone know if this is supported in the kernel?

The pinout for standard MMC according to the specification summary is:

Pin No. Name Type Description
1 RSV NC Reserved for future use
2 CMD I/O/PP/OD Command/Response
3 VSS1 S Supply voltage ground
4 VDD S Supply voltage
5 CLK I Clock
6 VSS2 S Supply voltage ground
7 DAT2 I/O/PP Data
Table 1: MultiMediaCard pad definition

from: http://www.mmca.org/compliance/buy_s...mary-v3.31.pdf

Doesn't have chip select, so may be it's done in the protocol?