thermal: core: Add a back up thermal shutdown mechanism

orderly_poweroff is triggered when a graceful shutdown
of system is desired. This may be used in many critical states of the
kernel such as when subsystems detects conditions such as critical
temperature conditions. However, in certain conditions in system
boot up sequences like those in the middle of driver probes being
initiated, userspace will be unable to power off the system in a clean
manner and leaves the system in a critical state. In cases like these,
the /sbin/poweroff will return success (having forked off to attempt
powering off the system. However, the system overall will fail to
completely poweroff (since other modules will be probed) and the system
is still functional with no userspace (since that would have shut itself
off).

However, there is no clean way of detecting such failure of userspace
powering off the system. In such scenarios, it is necessary for a backup
workqueue to be able to force a shutdown of the system when orderly
shutdown is not successful after a configurable time period.

Reported-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Keerthy <j-keerthy@ti.com>
Acked-by: Eduardo Valentin <edubezval@gmail.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>

Documentation/thermal/sysfs-api.txt

@@ -582,3 +582,24 @@ platform data is provided, this uses the step_wise throttling policy.
 This function serves as an arbitrator to set the state of a cooling
 device. It sets the cooling device to the deepest cooling state if
 possible.
+
+6. thermal_emergency_poweroff:
+
+On an event of critical trip temperature crossing. Thermal framework
+allows the system to shutdown gracefully by calling orderly_poweroff().
+In the event of a failure of orderly_poweroff() to shut down the system
+we are in danger of keeping the system alive at undesirably high
+temperatures. To mitigate this high risk scenario we program a work
+queue to fire after a pre-determined number of seconds to start
+an emergency shutdown of the device using the kernel_power_off()
+function. In case kernel_power_off() fails then finally
+emergency_restart() is called in the worst case.
+
+The delay should be carefully profiled so as to give adequate time for
+orderly_poweroff(). In case of failure of an orderly_poweroff() the
+emergency poweroff kicks in after the delay has elapsed and shuts down
+the system.
+
+If set to 0 emergency poweroff will not be supported. So a carefully
+profiled non-zero positive value is a must for emergerncy poweroff to be
+triggered.

drivers/thermal/Kconfig

@@ -15,6 +15,23 @@ menuconfig THERMAL
 
 if THERMAL
 
+config THERMAL_EMERGENCY_POWEROFF_DELAY_MS
+	int "Emergency poweroff delay in milli-seconds"
+	depends on THERMAL
+	default 0
+	help
+	  Thermal subsystem will issue a graceful shutdown when
+	  critical temperatures are reached using orderly_poweroff(). In
+	  case of failure of an orderly_poweroff(), the thermal emergency
+	  poweroff kicks in after a delay has elapsed and shuts down the system.
+	  This config is number of milliseconds to delay before emergency
+	  poweroff kicks in. Similarly to the critical trip point,
+	  the delay should be carefully profiled so as to give adequate
+	  time for orderly_poweroff() to finish on regular execution.
+	  If set to 0 emergency poweroff will not be supported.
+
+	  In doubt, leave as 0.
+
 config THERMAL_HWMON
 	bool
 	prompt "Expose thermal sensors as hwmon device"

drivers/thermal/thermal_core.c

@@ -324,6 +324,54 @@ static void handle_non_critical_trips(struct thermal_zone_device *tz,
 		       def_governor->throttle(tz, trip);
 }
 
+/**
+ * thermal_emergency_poweroff_func - emergency poweroff work after a known delay
+ * @work: work_struct associated with the emergency poweroff function
+ *
+ * This function is called in very critical situations to force
+ * a kernel poweroff after a configurable timeout value.
+ */
+static void thermal_emergency_poweroff_func(struct work_struct *work)
+{
+	/*
+	 * We have reached here after the emergency thermal shutdown
+	 * Waiting period has expired. This means orderly_poweroff has
+	 * not been able to shut off the system for some reason.
+	 * Try to shut down the system immediately using kernel_power_off
+	 * if populated
+	 */
+	WARN(1, "Attempting kernel_power_off: Temperature too high\n");
+	kernel_power_off();
+
+	/*
+	 * Worst of the worst case trigger emergency restart
+	 */
+	WARN(1, "Attempting emergency_restart: Temperature too high\n");
+	emergency_restart();
+}
+
+static DECLARE_DELAYED_WORK(thermal_emergency_poweroff_work,
+			    thermal_emergency_poweroff_func);
+
+/**
+ * thermal_emergency_poweroff - Trigger an emergency system poweroff
+ *
+ * This may be called from any critical situation to trigger a system shutdown
+ * after a known period of time. By default this is not scheduled.
+ */
+void thermal_emergency_poweroff(void)
+{
+	int poweroff_delay_ms = CONFIG_THERMAL_EMERGENCY_POWEROFF_DELAY_MS;
+	/*
+	 * poweroff_delay_ms must be a carefully profiled positive value.
+	 * Its a must for thermal_emergency_poweroff_work to be scheduled
+	 */
+	if (poweroff_delay_ms <= 0)
+		return;
+	schedule_delayed_work(&thermal_emergency_poweroff_work,
+			      msecs_to_jiffies(poweroff_delay_ms));
+}
+
 static void handle_critical_trips(struct thermal_zone_device *tz,
 				  int trip, enum thermal_trip_type trip_type)
 {
@@ -346,6 +394,11 @@ static void handle_critical_trips(struct thermal_zone_device *tz,
 			  tz->temperature / 1000);
 		mutex_lock(&poweroff_lock);
 		if (!power_off_triggered) {
+			/*
+			 * Queue a backup emergency shutdown in the event of
+			 * orderly_poweroff failure
+			 */
+			thermal_emergency_poweroff();
 			orderly_poweroff(true);
 			power_off_triggered = true;
 		}