[U-Boot] Questions about the mmc_spi driver

[Carl Perry]

I'm trying to get U-Boot working on the SiFive Freedom Unleased
u540-c000 board, and I have been following the RISC-V work here with
much excitement. I would like to have access to the SD card connected to
the SPI bus for reading kernels, storing configs and scripts, etc.
Unlike most ARM systems, which have a full SDIO port, the SD card is
attached to an SPI bus in MMC mode. Looking around, I found
drivers/mmc/mmc_spi.c which looks like it may do what I would like, but
it's config entry is not exposed in the Kconfig files anywhere. Is this
driver incomplete? I'm also unclear if just enabling it would have it
work as a "disk" or if it just becomes another "character device". I did
not find any docs, and the driver is 8 years old. Was this supposed to
be removed and is an oversight?


Any insights would be appreciated. Thanks!


  -Carl