| Andrei Warkentin | 371a689 | 2011-04-11 18:10:25 -0500 | [diff] [blame] | 1 | SD and MMC Device Partitions |
| 2 | ============================ |
| 3 | |
| 4 | Device partitions are additional logical block devices present on the |
| 5 | SD/MMC device. |
| 6 | |
| 7 | As of this writing, MMC boot partitions as supported and exposed as |
| 8 | /dev/mmcblkXboot0 and /dev/mmcblkXboot1, where X is the index of the |
| 9 | parent /dev/mmcblkX. |
| 10 | |
| 11 | MMC Boot Partitions |
| 12 | =================== |
| 13 | |
| 14 | Read and write access is provided to the two MMC boot partitions. Due to |
| 15 | the sensitive nature of the boot partition contents, which often store |
| 16 | a bootloader or bootloader configuration tables crucial to booting the |
| 17 | platform, write access is disabled by default to reduce the chance of |
| 18 | accidental bricking. |
| 19 | |
| 20 | To enable write access to /dev/mmcblkXbootY, disable the forced read-only |
| 21 | access with: |
| 22 | |
| 23 | echo 0 > /sys/block/mmcblkXbootY/force_ro |
| 24 | |
| 25 | To re-enable read-only access: |
| 26 | |
| 27 | echo 1 > /sys/block/mmcblkXbootY/force_ro |
| Johan Rudholm | add710e | 2011-12-02 08:51:06 +0100 | [diff] [blame] | 28 | |
| 29 | The boot partitions can also be locked read only until the next power on, |
| 30 | with: |
| 31 | |
| 32 | echo 1 > /sys/block/mmcblkXbootY/ro_lock_until_next_power_on |
| 33 | |
| 34 | This is a feature of the card and not of the kernel. If the card does |
| 35 | not support boot partition locking, the file will not exist. If the |
| 36 | feature has been disabled on the card, the file will be read-only. |
| 37 | |
| 38 | The boot partitions can also be locked permanently, but this feature is |
| 39 | not accessible through sysfs in order to avoid accidental or malicious |
| 40 | bricking. |