Here are the patches for Secure Digital support that I've been sitting 
on for a while. I tried to get some feedback on inclusion of this 
previously but since I didn't get any I'll just submit the thing.
It was originally diffed against 2.6.10 but it applies to 2.6.11 just 
fine (only minor fuzz).

Change summary:

* Detects if connected card is SD or MMC. Marks host as in SD mode if SD 
is detected (since SD isn't a bus system).
* Reads extra registers from SD cards (SCR) and parses CSD differently 
depending on SD/MMC mode.
* Support for 4-bit mode. This has been design to be fairly isolated 
from the SD bit so that it can (hopefully) be reused with MMC.
* New callback added for reading the read-only switch on SD cards.

Changed files:

mmc.c : SD detection and register parsing.
mmc_block.c : Checks read-only flag for cards (not SD-specific).
mmc_sysfs.c : Exposes SCR register.
card.h : Added flags to determine card type, RO and new register.
host.h : Added flags for bus width, RO test and mode (SD/MMC).
mmc.h : Added R6 define and new defines.
protocol.h : Added needed SD commands.

This patch is backwards compatible and only needs updated drivers to 
take advantage of 4-bit bus and reading the RO switch (unmodified 
drivers will default to 1-bit bus and write enable).

There might be new bugs that surface with this though. With my own 
drivers I discovered that very small transfers (< 16 bytes) always 
failed. Testing is needed but I do not have access to do it myself. MMC 
should not break with this since MMC is detected before SD.

Rgds
Pierre