[PATCH 1/2] thermal: Add notifier call chain for hot/critical events

[Ross Zwisler]

From: Duncan Laurie <dlaurie@xxxxxxxxxxxx>

This will allow drivers to register a callback for important
thermal events and log critical thresholds that cause the system
to shut down.

There are other places this might work, but after consideration
I think it makes sense to have the chain at this level:

The ACPI thermal driver has an existing notify function that is
eventually called into, but that would limit the notifier to only
working on systems that use ACPI.

The cpufreq driver is already getting a notify callback executed
in this path (tz->ops->notify) but the threshold info is not passed
to the cpu_cooling notifier chain so it is not useful for logging.

Signed-off-by: Duncan Laurie <dlaurie@xxxxxxxxxxxx>
Reviewed-by: Olof Johansson <olofj@xxxxxxxxxxxx>
Reviewed-by: Vincent Palatin <vpalatin@xxxxxxxxxxxx>
[ rez: updated changelog for upstream ]
Signed-off-by: Ross Zwisler <zwisler@xxxxxxxxxx>
---
 drivers/thermal/thermal_core.c | 38 ++++++++++++++++++++++++++++++++++
 include/linux/thermal.h        |  4 ++++
 2 files changed, 42 insertions(+)

diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
index 6ab982309e6a0..e1f8764b3d9f9 100644
--- a/drivers/thermal/thermal_core.c
+++ b/drivers/thermal/thermal_core.c
@@ -15,6 +15,7 @@
 #include <linux/slab.h>
 #include <linux/kdev_t.h>
 #include <linux/idr.h>
+#include <linux/notifier.h>
 #include <linux/thermal.h>
 #include <linux/reboot.h>
 #include <linux/string.h>
@@ -313,12 +314,46 @@ static void monitor_thermal_zone(struct thermal_zone_device *tz)
 	mutex_unlock(&tz->lock);
 }
 
+static BLOCKING_NOTIFIER_HEAD(thermal_notifier_list);
+
+/**
+ * register_thermal_notifier - Register function to be called for
+ *                             critical thermal events.
+ *
+ * @nb: Info about notifier function to be called
+ *
+ * Currently always returns zero, as blocking_notifier_chain_register()
+ * always returns zero.
+ */
+int register_thermal_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&thermal_notifier_list, nb);
+}
+EXPORT_SYMBOL(register_thermal_notifier);
+
+/**
+ * unregister_thermal_notifier - Unregister thermal notifier
+ *
+ * @nb: Hook to be unregistered
+ *
+ * Returns zero on success, or %-ENOENT on failure.
+ */
+int unregister_thermal_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&thermal_notifier_list, nb);
+}
+EXPORT_SYMBOL(unregister_thermal_notifier);
+
+
 static void handle_non_critical_trips(struct thermal_zone_device *tz,
 				      int trip,
 				      enum thermal_trip_type trip_type)
 {
 	tz->governor ? tz->governor->throttle(tz, trip) :
 		       def_governor->throttle(tz, trip);
+
+	blocking_notifier_call_chain(&thermal_notifier_list,
+				     trip_type, NULL);
 }
 
 /**
@@ -385,6 +420,9 @@ static void handle_critical_trips(struct thermal_zone_device *tz,
 	if (tz->ops->notify)
 		tz->ops->notify(tz, trip, trip_type);
 
+	blocking_notifier_call_chain(&thermal_notifier_list,
+				     trip_type, NULL);
+
 	if (trip_type == THERMAL_TRIP_CRITICAL) {
 		dev_emerg(&tz->device,
 			  "critical temperature reached (%d C), shutting down\n",
diff --git a/include/linux/thermal.h b/include/linux/thermal.h
index 5f4705f46c2f9..b948344d55cab 100644
--- a/include/linux/thermal.h
+++ b/include/linux/thermal.h
@@ -13,6 +13,7 @@
 #include <linux/of.h>
 #include <linux/idr.h>
 #include <linux/device.h>
+#include <linux/notifier.h>
 #include <linux/sysfs.h>
 #include <linux/workqueue.h>
 #include <uapi/linux/thermal.h>
@@ -542,4 +543,7 @@ static inline int thermal_generate_netlink_event(struct thermal_zone_device *tz,
 }
 #endif
 
+extern int register_thermal_notifier(struct notifier_block *);
+extern int unregister_thermal_notifier(struct notifier_block *);
+
 #endif /* __THERMAL_H__ */
-- 
2.19.1.568.g152ad8e336-goog