[U-Boot] RW filesystem support for new eMMC, eSD and eLBA flash devices

A relatively new class of flash memory device is available that generally consists of bulk NAND flash (SLC or MLC) and an on-board controller (that handles ECC and flash translation layer). (See http://www.micron.com/products/nand/managed-nand/index for example.) Can anyone tell me if u-boot supports read and write access to such a device? Of course I know u-boot can read/write nor, nand, and onenand flash, but can it write SD or MMC flash? From previous thread here I believe the answer is no for writing in the a filesystem's format (i.e. fat32 or ext3 for example). Is there a method to do "raw" writes?

Thanks, twebb