Add documentation what is default_spl_mmc_emmc_boot_partition() function doing, what each return value from this function means and why there is magic conversion from 7 to 0. Also add FIXME comment for future fixes.

All information is based on the JEDEC eMMC JESD84-A441 specification.

Signed-off-by: Pali Rohár pali@kernel.org

--- This patch depends on another patch: mmc: Use EXT_CSD_EXTRACT_BOOT_PART() macro for extracting boot part https://patchwork.ozlabs.org/project/uboot/patch/20230311104427.18421-1-pali... --- common/spl/spl_mmc.c | 42 +++++++++++++++++++++++++++++++++++++++--- 1 file changed, 39 insertions(+), 3 deletions(-)

diff --git a/common/spl/spl_mmc.c b/common/spl/spl_mmc.c index a0722167044f..2426500dbcb9 100644 --- a/common/spl/spl_mmc.c +++ b/common/spl/spl_mmc.c @@ -370,13 +370,49 @@ unsigned long __weak spl_mmc_get_uboot_raw_sector(struct mmc *mmc, int default_spl_mmc_emmc_boot_partition(struct mmc *mmc) { int part; + /* + * This function returns the eMMC partition from which + * would be loaded next payload (e.g. U-Boot proper). + * This partition will be set into eMMC partition access + * register and therefore return value of this function + * has same meaning as EXT_CSD_EXTRACT_PARTITION_ACCESS. + * + * Meaning of EXT_CSD_EXTRACT_PARTITION_ACCESS (3-bit) is: + * 0 - User area + * 1 - Boot partition 1 + * 2 - Boot partition 2 + * 3 - Replay Protected Memory Block (RPMB) + * 4 - General Purpose partition 1 + * 5 - General Purpose partition 2 + * 6 - General Purpose partition 3 + * 7 - General Purpose partition 4 + */ #ifdef CONFIG_SYS_MMCSD_RAW_MODE_EMMC_BOOT_PARTITION part = CONFIG_SYS_MMCSD_RAW_MODE_EMMC_BOOT_PARTITION; #else /* - * We need to check what the partition is configured to. - * 1 and 2 match up to boot0 / boot1 and 7 is user data - * which is the first physical partition (0). + * When explicit CONFIG_SYS_MMCSD_RAW_MODE_EMMC_BOOT_PARTITION + * config option was not chosen during build time we choose + * the boot partition based on the eMMC boot partition enable + * register (EXT_CSD_EXTRACT_BOOT_PART). + * + * Meaning of EXT_CSD_EXTRACT_BOOT_PART (3-bit) value is: + * 0 - Booting from this eMMC device is disabled + * 1 - Boot partition 1 is used for booting + * 2 - Boot partition 2 is used for booting + * 3 - Reserved + * 4 - Reserved + * 5 - Reserved + * 6 - Reserved + * 7 - User area is used for booting + * + * Note: See difference between EXT_CSD_EXTRACT_PARTITION_ACCESS + * and EXT_CSD_EXTRACT_BOOT_PART, specially about User area value. + * + * FIXME: When booting from this eMMC device is explicitly + * disabled then we use User area for booting. This is incorrect. + * Probably we should skip this eMMC device and select the next + * one for booting. Or at least throw warning about this fallback. */ part = EXT_CSD_EXTRACT_BOOT_PART(mmc->part_config); if (part == 7)