ACPI: Allow overriding to higher critical trip point.

http://bugzilla.kernel.org/show_bug.cgi?id=9129

lenb: Note that overriding a critical trip point
may simply fool the user into thinking that they
have control that they do not actually have.
For it is EC firmware that decides when the EC
sends Linux temperature change events, and the
EC may or may not decide to send Linux these events
anywhere in the neighborhood of the fake
override trip points.  Beware.

note also that thermal.nocrt is already available
to disable crtical trip point actios,
and thermal.crt=-1 is already available to
disabled critical trip points entirely.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

Documentation/kernel-parameters.txt

@@ -2146,7 +2146,7 @@ and is between 256 and 4096 characters. It is defined in the file
 
 	thermal.crt=	[HW,ACPI]
 			-1: disable all critical trip points in all thermal zones
-			<degrees C>: lower all critical trip points
+			<degrees C>: override all critical trip points
 
 	thermal.nocrt=	[HW,ACPI]
 			Set to disable actions on ACPI thermal zone

drivers/acpi/thermal.c

@@ -388,10 +388,12 @@ static int acpi_thermal_trips_update(struct acpi_thermal *tz, int flag)
 			} else if (crt > 0) {
 				unsigned long crt_k = CELSIUS_TO_KELVIN(crt);
 				/*
-				 * Allow override to lower critical threshold
+				 * Allow override critical threshold
 				 */
-				if (crt_k < tz->trips.critical.temperature)
-					tz->trips.critical.temperature = crt_k;
+				if (crt_k > tz->trips.critical.temperature)
+					printk(KERN_WARNING PREFIX
+						"Critical threshold %d C\n", crt);
+				tz->trips.critical.temperature = crt_k;
 			}
 		}
 	}