[PATCH v5] Input: sysrq - DT binding for key sequence

[mathieu.poirier at linaro.org]

From: "Mathieu J. Poirier" <mathieu.poirier at linaro.org>

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 at linaro.org>
---
changes for v5:
  - Corrected error in binding definition.
  - Using helper macro to fetch the key sequence.
  - Removing white space.
---
 .../devicetree/bindings/input/input-reset.txt      | 34 ++++++++++++++++++++
 drivers/tty/sysrq.c                                | 37 ++++++++++++++++++++++
 2 files changed, 71 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/input/input-reset.txt

diff --git a/Documentation/devicetree/bindings/input/input-reset.txt b/Documentation/devicetree/bindings/input/input-reset.txt
new file mode 100644
index 0000000..c69390c
--- /dev/null
+++ b/Documentation/devicetree/bindings/input/input-reset.txt
@@ -0,0 +1,34 @@
+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 keycodes
+
+Optional property:
+timeout-ms: duration keys must be pressed together in milliseconds
+before generating a sysrq
+
+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 b51c154..ed8f00f 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -44,6 +44,7 @@
 #include <linux/uaccess.h>
 #include <linux/moduleparam.h>
 #include <linux/jiffies.h>
+#include <linux/of.h>
 
 #include <asm/ptrace.h>
 #include <asm/irq_regs.h>
@@ -671,6 +672,34 @@ static void sysrq_detect_reset_sequence(struct sysrq_state *state,
 	}
 }
 
+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);
+}
+
 static void sysrq_reinject_alt_sysrq(struct work_struct *work)
 {
 	struct sysrq_state *sysrq =
@@ -903,6 +932,7 @@ 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)
@@ -911,6 +941,13 @@ 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);
-- 
1.8.1.2