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>

2 files changed, 75 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/input/input-reset.txt b/Documentation/devicetree/bindings/input/input-reset.txt
new file mode 100644
index 000000000000..2bb2626fdb78
--- /dev/null
+++ b/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.
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 55ba46f6207d..749dae8c3489 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -45,6 +45,7 @@
 #include <linux/moduleparam.h>
 #include <linux/jiffies.h>
 #include <linux/syscalls.h>
+#include <linux/of.h>
 
 #include <asm/ptrace.h>
 #include <asm/irq_regs.h>
@@ -681,6 +682,40 @@ static void sysrq_detect_reset_sequence(struct sysrq_state *state,
         }
 }
 
+#ifdef CONFIG_OF
+static void sysrq_of_get_keyreset_config(void)
+{
+        u32 key;
+        struct device_node *np;
+        struct property *prop;
+        const __be32 *p;
+
+        np = of_find_node_by_path("/chosen/linux,sysrq-reset-seq");
+        if (!np) {
+                pr_debug("No sysrq node found");
+                return;
+        }
+
+        /* Reset in case a __weak definition was present */
+        sysrq_reset_seq_len = 0;
+
+        of_property_for_each_u32(np, "keyset", prop, p, key) {
+                if (key == KEY_RESERVED || key > KEY_MAX ||
+                    sysrq_reset_seq_len == SYSRQ_KEY_RESET_MAX)
+                        break;
+
+                sysrq_reset_seq[sysrq_reset_seq_len++] = (unsigned short)key;
+        }
+
+        /* Get reset timeout if any. */
+        of_property_read_u32(np, "timeout-ms", &sysrq_reset_downtime_ms);
+}
+#else
+static void sysrq_of_get_keyreset_config(void)
+{
+}
+#endif
+
 static void sysrq_reinject_alt_sysrq(struct work_struct *work)
 {
         struct sysrq_state *sysrq =
@@ -914,6 +949,7 @@ static inline void sysrq_register_handler(void)
         int error;
         int i;
 
+        /* First check if a __weak interface was instantiated. */
         for (i = 0; i < ARRAY_SIZE(sysrq_reset_seq); i++) {
                 key = platform_sysrq_reset_seq[i];
                 if (key == KEY_RESERVED || key > KEY_MAX)
@@ -922,6 +958,12 @@ static inline void sysrq_register_handler(void)
                 sysrq_reset_seq[sysrq_reset_seq_len++] = key;
         }
 
+        /*
+         * DT configuration takes precedence over anything that would
+         * have been defined via the __weak interface.
+         */
+        sysrq_of_get_keyreset_config();
+
         error = input_register_handler(&sysrq_handler);
         if (error)
                 pr_err("Failed to register input handler, error %d", error);