| ============================ |
| 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. |
