mmc: boot partition ro lock support

Enable boot partitions to be read-only locked until next power on via
a sysfs entry. There will be one sysfs entry for each boot partition:

/sys/block/mmcblkXbootY/ro_lock_until_next_power_on

Each boot partition is locked by writing 1 to its file.

Signed-off-by: Johan Rudholm <johan.rudholm@stericsson.com>
Signed-off-by: John Beckett <john.beckett@stericsson.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/Documentation/mmc/mmc-dev-parts.txt b/Documentation/mmc/mmc-dev-parts.txt
index 2db28b8e662..f08d078d43c 100644
--- a/Documentation/mmc/mmc-dev-parts.txt
+++ b/Documentation/mmc/mmc-dev-parts.txt
@@ -25,3 +25,16 @@ 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.