MMC/SD over SPI

modulename: mmc_spi.ko

and/or

of_mmc_spi.ko

configname: CONFIG_MMC_SPI

Linux Kernel Configuration
└─>Device Drivers
└─>MMC/SD card support
└─>MMC/SD over SPI
In linux kernel since version 2.6.24 (release Date: 2008-01-24)  
Some systems accss MMC/SD cards using a SPI controller instead of
using a "native" MMC/SD controller. This has a disadvantage of
being relatively high overhead, but a compensating advantage of
working on many systems without dedicated MMC/SD controllers.

If unsure, or if your system has no SPI master driver, say N.

source code: