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| -rw-r--r-- | Documentation/driver-api/mmc/mmc-dev-parts.rst | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/Documentation/driver-api/mmc/mmc-dev-parts.rst b/Documentation/driver-api/mmc/mmc-dev-parts.rst new file mode 100644 index 000000000..995922f1f --- /dev/null +++ b/Documentation/driver-api/mmc/mmc-dev-parts.rst @@ -0,0 +1,41 @@ +============================ +SD and MMC Device Partitions +============================ + +Device partitions are additional logical block devices present on the +SD/MMC device. + +As of this writing, MMC boot partitions as supported and exposed as +/dev/mmcblkXboot0 and /dev/mmcblkXboot1, where X is the index of the +parent /dev/mmcblkX. + +MMC Boot Partitions +=================== + +Read and write access is provided to the two MMC boot partitions. Due to +the sensitive nature of the boot partition contents, which often store +a bootloader or bootloader configuration tables crucial to booting the +platform, write access is disabled by default to reduce the chance of +accidental bricking. + +To enable write access to /dev/mmcblkXbootY, disable the forced read-only +access with:: + + echo 0 > /sys/block/mmcblkXbootY/force_ro + +To re-enable read-only access:: + + echo 1 > /sys/block/mmcblkXbootY/force_ro + +The boot partitions can also be locked read only until the next power on, +with:: + + echo 1 > /sys/block/mmcblkXbootY/ro_lock_until_next_power_on + +This is a feature of the card and not of the kernel. If the card does +not support boot partition locking, the file will not exist. If the +feature has been disabled on the card, the file will be read-only. + +The boot partitions can also be locked permanently, but this feature is +not accessible through sysfs in order to avoid accidental or malicious +bricking. |