1 ============================ 1 ============================
2 SD and MMC Device Partitions 2 SD and MMC Device Partitions
3 ============================ 3 ============================
4 4
5 Device partitions are additional logical block 5 Device partitions are additional logical block devices present on the
6 SD/MMC device. 6 SD/MMC device.
7 7
8 As of this writing, MMC boot partitions as sup 8 As of this writing, MMC boot partitions as supported and exposed as
9 /dev/mmcblkXboot0 and /dev/mmcblkXboot1, where 9 /dev/mmcblkXboot0 and /dev/mmcblkXboot1, where X is the index of the
10 parent /dev/mmcblkX. 10 parent /dev/mmcblkX.
11 11
12 MMC Boot Partitions 12 MMC Boot Partitions
13 =================== 13 ===================
14 14
15 Read and write access is provided to the two M 15 Read and write access is provided to the two MMC boot partitions. Due to
16 the sensitive nature of the boot partition con 16 the sensitive nature of the boot partition contents, which often store
17 a bootloader or bootloader configuration table 17 a bootloader or bootloader configuration tables crucial to booting the
18 platform, write access is disabled by default 18 platform, write access is disabled by default to reduce the chance of
19 accidental bricking. 19 accidental bricking.
20 20
21 To enable write access to /dev/mmcblkXbootY, d 21 To enable write access to /dev/mmcblkXbootY, disable the forced read-only
22 access with:: 22 access with::
23 23
24 echo 0 > /sys/block/mmcblkXbootY/force 24 echo 0 > /sys/block/mmcblkXbootY/force_ro
25 25
26 To re-enable read-only access:: 26 To re-enable read-only access::
27 27
28 echo 1 > /sys/block/mmcblkXbootY/force 28 echo 1 > /sys/block/mmcblkXbootY/force_ro
29 29
30 The boot partitions can also be locked read on 30 The boot partitions can also be locked read only until the next power on,
31 with:: 31 with::
32 32
33 echo 1 > /sys/block/mmcblkXbootY/ro_lo 33 echo 1 > /sys/block/mmcblkXbootY/ro_lock_until_next_power_on
34 34
35 This is a feature of the card and not of the k 35 This is a feature of the card and not of the kernel. If the card does
36 not support boot partition locking, the file w 36 not support boot partition locking, the file will not exist. If the
37 feature has been disabled on the card, the fil 37 feature has been disabled on the card, the file will be read-only.
38 38
39 The boot partitions can also be locked permane 39 The boot partitions can also be locked permanently, but this feature is
40 not accessible through sysfs in order to avoid 40 not accessible through sysfs in order to avoid accidental or malicious
41 bricking. 41 bricking.
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