Input: sysrq - DT binding for key sequence

Adding a simple device tree binding for the specification of key
sequences. Definition of the keys found in the sequence are located in
'include/uapi/linux/input.h'.

For the sysrq driver, holding the sequence of keys down for a specific
amount of time will reset the system.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Acked-by: Grant Likely <grant.likely@linaro.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/input-reset.txt

@@ -0,0 +1,33 @@
+Input: sysrq reset sequence
+
+A simple binding to represent a set of keys as described in
+include/uapi/linux/input.h. This is to communicate a sequence of keys to the
+sysrq driver. Upon holding the keys for a specified amount of time (if
+specified) the system is sync'ed and reset.
+
+Key sequences are global to the system but all the keys in a set must be coming
+from the same input device.
+
+The /chosen node should contain a 'linux,sysrq-reset-seq' child node to define
+a set of keys.
+
+Required property:
+sysrq-reset-seq: array of Linux keycodes, one keycode per cell.
+
+Optional property:
+timeout-ms: duration keys must be pressed together in milliseconds before
+generating a sysrq. If omitted the system is rebooted immediately when a valid
+sequence has been recognized.
+
+Example:
+
+ chosen {
+                linux,sysrq-reset-seq {
+                        keyset = <0x03
+                                  0x04
+                                  0x0a>;
+                        timeout-ms = <3000>;
+                };
+         };
+
+Would represent KEY_2, KEY_3 and KEY_9.