[PATCH v4 2/3] reboot: Introduce hw_protection_reboot()

[Fabio Estevam <festevam@gmail.com>]

From: Fabio Estevam <festevam@denx.de>

Introduce hw_protection_reboot() to trigger an emergency reboot.

It is a counterpart of hw_protection_shutdown() with the difference
that it will force a reboot instead of shutdown.

The motivation for doing this is to allow the thermal subystem
to trigger a reboot when the temperature reaches the critical
temperature.

Signed-off-by: Fabio Estevam <festevam@denx.de>
---
Changes since v3:
- None

 include/linux/reboot.h |  1 +
 kernel/reboot.c        | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/include/linux/reboot.h b/include/linux/reboot.h
index 2b6bb593be5b..4a319bc24f6a 100644
--- a/include/linux/reboot.h
+++ b/include/linux/reboot.h
@@ -174,6 +174,7 @@ void ctrl_alt_del(void);
 
 extern void orderly_poweroff(bool force);
 extern void orderly_reboot(void);
+void hw_protection_reboot(const char *reason, int ms_until_forced);
 void hw_protection_shutdown(const char *reason, int ms_until_forced);
 
 /*
diff --git a/kernel/reboot.c b/kernel/reboot.c
index 3bba88c7ffc6..05333ae8bc6b 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -952,6 +952,40 @@ static void hw_failure_emergency_poweroff(int poweroff_delay_ms)
 			      msecs_to_jiffies(poweroff_delay_ms));
 }
 
+/**
+ * hw_protection_reboot - Trigger an emergency system reboot
+ *
+ * @reason:		Reason of emergency reboot to be printed.
+ * @ms_until_forced:	Time to wait for orderly reboot before tiggering a
+ *			forced reboot. Negative value disables the forced
+ *			reboot.
+ *
+ * Initiate an emergency system reboot in order to protect hardware from
+ * further damage. Usage examples include a thermal protection.
+ *
+ * NOTE: The request is ignored if protection reboot is already pending even
+ * if the previous request has given a large timeout for forced reboot.
+ * Can be called from any context.
+ */
+void hw_protection_reboot(const char *reason, int ms_until_forced)
+{
+	static atomic_t allow_proceed = ATOMIC_INIT(1);
+
+	pr_emerg("HARDWARE PROTECTION reboot (%s)\n", reason);
+
+	/* Reboot should be initiated only once. */
+	if (!atomic_dec_and_test(&allow_proceed))
+		return;
+
+	/*
+	 * Queue a backup emergency reboot in the event of
+	 * orderly_reboot failure
+	 */
+	hw_failure_emergency_poweroff(ms_until_forced);
+	orderly_reboot();
+}
+EXPORT_SYMBOL_GPL(hw_protection_reboot);
+
 /**
  * hw_protection_shutdown - Trigger an emergency system poweroff
  *
-- 
2.34.1