Add a new LED trigger for kernel panics (and use it)

This commit introduces a new LED trigger which allows to configure a LED to blink on a kernel panic (through panic_blink).

Notice that currently the Openmoko FreeRunner (GTA02) mach code sets panic_blink to blink a hard-coded LED. The new trigger is meant to introduce a generic mechanism to achieve this.

Signed-off-by Ezequiel Garcia <[email protected]>

---
  drivers/leds/trigger/Kconfig         |  7 +++++++
  drivers/leds/trigger/Makefile        |  1 +
  drivers/leds/trigger/ledtrig-panic.c | 30 ++++++++++++++++++++++++++++++
  3 files changed, 38 insertions(+)

create mode 100644 drivers/leds/trigger/ledtrig-panic.c

drivers/leds/trigger/Kconfig +7 -0

index 5bda6a9b56bb..554f5bfbeced 100644
@@ -108,4 +108,11 @@ config LEDS_TRIGGER_CAMERA
  	  This enables direct flash/torch on/off by the driver, kernel space.
  	  If unsure, say Y.
 
+config LEDS_TRIGGER_PANIC
+	bool "LED Panic Trigger"
+	depends on LEDS_TRIGGERS
+	help
+	  This allows LEDs to be configured to blink on a kernel panic.
+	  If unsure, say Y.
+
  endif # LEDS_TRIGGERS

drivers/leds/trigger/Makefile +1 -0

index 1abf48dacf7e..547bf5c80e52 100644
@@ -8,3 +8,4 @@ obj-$(CONFIG_LEDS_TRIGGER_CPU)		+= ledtrig-cpu.o
  obj-$(CONFIG_LEDS_TRIGGER_DEFAULT_ON)	+= ledtrig-default-on.o
  obj-$(CONFIG_LEDS_TRIGGER_TRANSIENT)	+= ledtrig-transient.o
  obj-$(CONFIG_LEDS_TRIGGER_CAMERA)	+= ledtrig-camera.o
+obj-$(CONFIG_LEDS_TRIGGER_PANIC)	+= ledtrig-panic.o

drivers/leds/trigger/ledtrig-panic.c new file +30 -0

new file mode 100644
index 000000000000..627b350c5ec3
@@ -0,0 +1,30 @@
+/*
+ * Kernel Panic LED Trigger
+ *
+ * Copyright 2016 Ezequiel Garcia <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/leds.h>
+
+static struct led_trigger *trigger;
+
+static long led_panic_blink(int state)
+{
+	led_trigger_event(trigger, state ? LED_FULL : LED_OFF);
+	return 0;
+}
+
+static int __init ledtrig_panic_init(void)
+{
+	led_trigger_register_simple("panic", &trigger);
+	panic_blink = led_panic_blink;
+	return 0;
+}
+device_initcall(ledtrig_panic_init);

Hi Ezequiel,

Thanks for the patch. I've tested it on exynos4412-trats2 board with leds-aat1290 driver, by executing:

echo "c" > /proc/sysrq-trigger

I was able to notice the blinking then.

Applied to the for-next branch of linux-leds.git.

+lkml

Quoted 11 lines · Jacek Anaszewski

Hi Ezequiel,

Thanks for the patch. I've tested it on exynos4412-trats2 board with leds-aat1290 driver, by executing:

echo "c" > /proc/sysrq-trigger

I was able to notice the blinking then.

Applied to the for-next branch of linux-leds.git.

Notice that we currently need LEDs to be dedicated to the panic trigger, which is pretty lame as LEDs are scarce and are most likely assigned to something else.

So, here's a toy patch to switch all the installed LEDs to the panic trigger on kernel panic. Patch is half-baked, but it shows the idea.

(Interestingly, it also blinks the LEDs on a USB keyboard!)

Is there any value in polishing this and find a way upstream?

drivers/leds/led-class.c +16 -0

index aa84e5b37593..caaf6161a7ae 100644
@@ -321,6 +321,20 @@ void devm_led_classdev_unregister(struct device *dev,
  }
  EXPORT_SYMBOL_GPL(devm_led_classdev_unregister);
 
+static int led_panic_notifier(struct notifier_block *nb,
+			      unsigned long code, void *unused)
+{
+	struct led_classdev *led_cdev;
+
+	list_for_each_entry(led_cdev, &leds_list, node)
+		led_trigger_set_at_panic(led_cdev, "panic");
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block led_panic_nb = {
+	.notifier_call = led_panic_notifier,
+};
+
  static int __init leds_init(void)
  {
  	leds_class = class_create(THIS_MODULE, "leds");

@@ -328,6 +342,8 @@ static int __init leds_init(void)
  		return PTR_ERR(leds_class);
  	leds_class->pm = &leds_class_dev_pm_ops;
  	leds_class->dev_groups = led_groups;
+	atomic_notifier_chain_register(&panic_notifier_list,
+				       &led_panic_nb);
  	return 0;
  }
 

drivers/leds/led-triggers.c +0 -0

index 2181581795d3..8c1d33acdfa8 100644

drivers/leds/led-triggers.c +13 -0

+	struct led_trigger *trig;
+
+	list_for_each_entry(trig, &trigger_list, next_trig) {
+		if (strcmp(name, trig->name))
+			continue;
+		list_add_tail(&led_cdev->trig_list, &trig->led_cdevs);
+		led_cdev->trigger = trig;
+		if (trig->activate)
+			trig->activate(led_cdev);
+		break;
+	}
+}
+
  void led_trigger_set_default(struct led_classdev *led_cdev)
  {
  	struct led_trigger *trig;

drivers/leds/leds.h +1 -0

index db3f20da7221..8cfa10f626a6 100644
@@ -21,6 +21,7 @@ static inline int led_get_brightness(struct led_classdev *led_cdev)
  	return led_cdev->brightness;
  }
 
+void led_trigger_set_at_panic(struct led_classdev *led_cdev, const char *name);
  void led_init_core(struct led_classdev *led_cdev);
  void led_stop_software_blink(struct led_classdev *led_cdev);
  void led_set_brightness_nopm(struct led_classdev *led_cdev,

Hi Ezequiel,

Quoted 19 lines · Ezequiel Garcia

+lkml

Quoted 11 lines · Jacek Anaszewski

Hi Ezequiel,

Thanks for the patch. I've tested it on exynos4412-trats2 board with leds-aat1290 driver, by executing:

echo "c" > /proc/sysrq-trigger

I was able to notice the blinking then.

Applied to the for-next branch of linux-leds.git.

Notice that we currently need LEDs to be dedicated to the panic trigger, which is pretty lame as LEDs are scarce and are most likely assigned to something else.

Quoted 7 lines

So, here's a toy patch to switch all the installed LEDs to the panic trigger on kernel panic. Patch is half-baked, but it shows the idea.

(Interestingly, it also blinks the LEDs on a USB keyboard!)

Is there any value in polishing this and find a way upstream?

I like the idea, but I'd rather explicitly mark LEDs as panic indicators.

How about adding a "kernel-panic-indicator" Device Tree property to common LED bindings? LED class device could be registered for the panic trigger on kernel panic notification only when the property is present.

Adding Rob, Mark and devicetree list.

Quoted 40 lines

drivers/leds/led-class.c +14 -0

index aa84e5b37593..caaf6161a7ae 100644
@@ -321,6 +321,20 @@ void devm_led_classdev_unregister(struct device
 *dev,
  }
  EXPORT_SYMBOL_GPL(devm_led_classdev_unregister);
 
+static int led_panic_notifier(struct notifier_block *nb,
+                  unsigned long code, void *unused)
+{
+    struct led_classdev *led_cdev;
+
+    list_for_each_entry(led_cdev, &leds_list, node)
+        led_trigger_set_at_panic(led_cdev, "panic");
+    return NOTIFY_DONE;
+}
+
+static struct notifier_block led_panic_nb = {
+    .notifier_call = led_panic_notifier,
+};
+
  static int __init leds_init(void)
  {

      leds_class = class_create(THIS_MODULE, "leds");

drivers/leds/led-class.c +2 -0

@@ -328,6 +342,8 @@ static int __init leds_init(void)
          return PTR_ERR(leds_class);
      leds_class->pm = &leds_class_dev_pm_ops;
      leds_class->dev_groups = led_groups;
+    atomic_notifier_chain_register(&panic_notifier_list,
+                       &led_panic_nb);
      return 0;
  }
 

drivers/leds/led-triggers.c +0 -0

index 2181581795d3..8c1d33acdfa8 100644

drivers/leds/led-triggers.c void led_trigger_remove(struct led_classdev · line 154

Quoted 7 lines

drivers/leds/led-triggers.c +2 -0

@@ -148,6 +148,21 @@ void led_trigger_remove(struct led_classdev
 *led_cdev)
  }
  EXPORT_SYMBOL_GPL(led_trigger_remove);
 
+void led_trigger_set_at_panic(struct led_classdev *led_cdev, const
 char *name)
+{

"name" parameter is not required, since setting other trigger than panic on kernel panic doesn't make sense.

Quoted 31 lines

drivers/leds/led-triggers.c +13 -0

+    struct led_trigger *trig;
+
+    list_for_each_entry(trig, &trigger_list, next_trig) {
+        if (strcmp(name, trig->name))
+            continue;
+        list_add_tail(&led_cdev->trig_list, &trig->led_cdevs);
+        led_cdev->trigger = trig;
+        if (trig->activate)
+            trig->activate(led_cdev);
+        break;
+    }
+}
+
  void led_trigger_set_default(struct led_classdev *led_cdev)

  {
      struct led_trigger *trig;

drivers/leds/leds.h +1 -0

index db3f20da7221..8cfa10f626a6 100644
@@ -21,6 +21,7 @@ static inline int led_get_brightness(struct
 led_classdev *led_cdev)
      return led_cdev->brightness;
  }
 
+void led_trigger_set_at_panic(struct led_classdev *led_cdev, const
 char *name);
  void led_init_core(struct led_classdev *led_cdev);

void led_stop_software_blink(struct led_classdev *led_cdev); void led_set_brightness_nopm(struct led_classdev *led_cdev,

(Interestingly, it also blinks the LEDs on a USB keyboard!)

This patchset adds a very simple kernel panic LED trigger, by hooking into panic_blink. I've tested this trigger on ARM Armada XP OpenBlocks AX3-4 machine.

The trigger is then used to replace the open-coded panic_blink usage in GTA02 board.

Note that I don't have a GTA02 board, so the last patch is only built tested.

Ezequiel Garcia (3):
leds: trigger: Introduce a kernel panic LED trigger
ARM: configs: Enable panic LED trigger on s3c2410
ARM: s3c24xx: Use the panic LED trigger for GTA02

 arch/arm/configs/s3c2410_defconfig   |  1 +
 arch/arm/mach-s3c24xx/mach-gta02.c   | 35 ++++++++++++++++-------------------
 drivers/leds/trigger/Kconfig         |  7 +++++++
 drivers/leds/trigger/Makefile        |  1 +
 drivers/leds/trigger/ledtrig-panic.c | 30 ++++++++++++++++++++++++++++++
 5 files changed, 55 insertions(+), 19 deletions(-)
 create mode 100644 drivers/leds/trigger/ledtrig-panic.c