ACPI: thermal: create "thermal.crt=C" bootparam

Some hardware will malfunction at a temperature below
the BIOS provided critical shutdown threshold.

This hook allows moving the critical trip points down
to a temperature which provokes a graceful shutdown
before the hardware malfunction.

http://bugzilla.kernel.org/show_bug.cgi?id=8884

WARNING: A trip-point override will not get noticed
until the system delivers a temperature change event,
or unless thermal zone polling is enabled.
eg. "thermal.tzp=10"
Signed-off-by: Len Brown <len.brown@intel.com>

Documentation/kernel-parameters.txt

@@ -1826,6 +1826,10 @@ and is between 256 and 4096 characters. It is defined in the file
 			-1: disable all active trip points in all thermal zones
 			<degrees C>: override all lowest active trip points
 
+	thermal.crt=	[HW,ACPI]
+			-1: disable all critical trip points in all thermal zones
+			<degrees C>: lower all critical trip points
+
 	thermal.nocrt=	[HW,ACPI]
 			Set to disable actions on ACPI thermal zone
 			critical and hot trip points.

drivers/acpi/thermal.c

@@ -79,6 +79,10 @@ static int act;
 module_param(act, int, 0644);
 MODULE_PARM_DESC(act, "Disable or override all lowest active trip points.");
 
+static int crt;
+module_param(crt, int, 0644);
+MODULE_PARM_DESC(crt, "Disable or lower all critical trip points.");
+
 static int tzp;
 module_param(tzp, int, 0444);
 MODULE_PARM_DESC(tzp, "Thermal zone polling frequency, in 1/10 seconds.");
@@ -340,6 +344,20 @@ static int acpi_thermal_get_trip_points(struct acpi_thermal *tz)
 				  tz->trips.critical.temperature));
 	}
 
+	if (tz->trips.critical.flags.valid == 1) {
+		if (crt == -1) {
+			tz->trips.critical.flags.valid = 0;
+		} else if (crt > 0) {
+			unsigned long crt_k = CELSIUS_TO_KELVIN(crt);
+
+			/*
+			 * Allow override to lower critical threshold
+			 */
+			if (crt_k < tz->trips.critical.temperature)
+				tz->trips.critical.temperature = crt_k;
+		}
+	}
+
 	/* Critical Sleep (optional) */
 
 	status =