sdmmc_open
if ((error = sdmmc_open(of, unit, part)) != 0)
int sdmmc_open(struct open_file *, ...);
{ "s3c sdio", sdmmc_strategy, sdmmc_open, sdmmc_close, noioctl }
.dv_open = sdmmc_open,
error = sdmmc_open(f, fname, file);
int sdmmc_open(struct open_file *, ...);