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Documentation / mmc / mmc-dev-parts.txt




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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:03 EST.

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
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.
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