leds: triggers: Allow to switch the trigger to "panic" on a kernel panic

This commit adds a new led_cdev flag LED_PANIC_INDICATOR, which
allows to mark a specific LED to be switched to the "panic"
trigger, on a kernel panic.

This is useful to allow the user to assign a regular trigger
to a given LED, and still blink that LED on a kernel panic.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Reviewed-by: Matthias Brugger <mbrugger@suse.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>

2 files changed, 50 insertions, 0 deletions

diff --git a/drivers/leds/trigger/Kconfig b/drivers/leds/trigger/Kconfig
index beac8c31c51b..9893d911390d 100644
--- a/drivers/leds/trigger/Kconfig
+++ b/drivers/leds/trigger/Kconfig
@@ -121,6 +121,9 @@ config LEDS_TRIGGER_PANIC
         depends on LEDS_TRIGGERS
         help
           This allows LEDs to be configured to blink on a kernel panic.
+          Enabling this option will allow to mark certain LEDs as panic indicators,
+          allowing to blink them on a kernel panic, even if they are set to
+          a different trigger.
           If unsure, say Y.
 
 endif # LEDS_TRIGGERS
diff --git a/drivers/leds/trigger/ledtrig-panic.c b/drivers/leds/trigger/ledtrig-panic.c
index 627b350c5ec3..d735526b9db4 100644
--- a/drivers/leds/trigger/ledtrig-panic.c
+++ b/drivers/leds/trigger/ledtrig-panic.c
@@ -11,10 +11,54 @@
 
 #include <linux/kernel.h>
 #include <linux/init.h>
+#include <linux/notifier.h>
 #include <linux/leds.h>
+#include "../leds.h"
 
 static struct led_trigger *trigger;
 
+/*
+ * This is called in a special context by the atomic panic
+ * notifier. This means the trigger can be changed without
+ * worrying about locking.
+ */
+static void led_trigger_set_panic(struct led_classdev *led_cdev)
+{
+        struct led_trigger *trig;
+
+        list_for_each_entry(trig, &trigger_list, next_trig) {
+                if (strcmp("panic", trig->name))
+                        continue;
+                if (led_cdev->trigger)
+                        list_del(&led_cdev->trig_list);
+                list_add_tail(&led_cdev->trig_list, &trig->led_cdevs);
+
+                /* Avoid the delayed blink path */
+                led_cdev->blink_delay_on = 0;
+                led_cdev->blink_delay_off = 0;
+
+                led_cdev->trigger = trig;
+                if (trig->activate)
+                        trig->activate(led_cdev);
+                break;
+        }
+}
+
+static int led_trigger_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)
+                if (led_cdev->flags & LED_PANIC_INDICATOR)
+                        led_trigger_set_panic(led_cdev);
+        return NOTIFY_DONE;
+}
+
+static struct notifier_block led_trigger_panic_nb = {
+        .notifier_call = led_trigger_panic_notifier,
+};
+
 static long led_panic_blink(int state)
 {
         led_trigger_event(trigger, state ? LED_FULL : LED_OFF);
@@ -23,6 +67,9 @@ static long led_panic_blink(int state)
 
 static int __init ledtrig_panic_init(void)
 {
+        atomic_notifier_chain_register(&panic_notifier_list,
+                                       &led_trigger_panic_nb);
+
         led_trigger_register_simple("panic", &trigger);
         panic_blink = led_panic_blink;
         return 0;