Passing the index of booting MMC interface from SPL to u-boot.bin

On beaglebone black, which are based on TI AM3358, the booting of U-Boot is split into two phrases, MLO and u-boot.bin/img. There should be a way to pass the index of the booting MMC interface from MLO to u-boot, so that the uboot.env in the FAT file system on the booting card could be read from the booting MMC, rather than by the static configuration "ENV_FAT_DEVICE_AND_PART". A patch has been compiled and the same MLO and u-boot.bin/img pair could be used for both the eMMC and the uSD card for boot. I'd like to know where should I send this patch for review?

Thanks, Dashi Cao