ACPI: Adjust Kelvin offset to match local implementation
The exact offset between Kelvin and degree Celsius is 273.15. However
ACPI handles temperature values with a single decimal place. As a
consequence, some implementations use an offset of 273.1 and others
use an offset of 273.2. Try to find out which one is being used, to
present the most accurate and visually appealing number.
Tested on a Sony Vaio PGC-GR214EP (which uses 273.1) and a Lenovo
Thinkpad T60p (which uses 273.2).
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/drivers/acpi/thermal.c b/drivers/acpi/thermal.c
index e8c143c..ddbb7c8f 100644
--- a/drivers/acpi/thermal.c
+++ b/drivers/acpi/thermal.c
@@ -192,6 +192,7 @@
struct acpi_handle_list devices;
struct thermal_zone_device *thermal_zone;
int tz_enabled;
+ int kelvin_offset;
struct mutex lock;
};
@@ -581,7 +582,7 @@
}
/* sys I/F for generic thermal sysfs support */
-#define KELVIN_TO_MILLICELSIUS(t) (t * 100 - 273200)
+#define KELVIN_TO_MILLICELSIUS(t, off) (((t) - (off)) * 100)
static int thermal_get_temp(struct thermal_zone_device *thermal,
unsigned long *temp)
@@ -596,7 +597,7 @@
if (result)
return result;
- *temp = KELVIN_TO_MILLICELSIUS(tz->temperature);
+ *temp = KELVIN_TO_MILLICELSIUS(tz->temperature, tz->kelvin_offset);
return 0;
}
@@ -702,7 +703,8 @@
if (tz->trips.critical.flags.valid) {
if (!trip) {
*temp = KELVIN_TO_MILLICELSIUS(
- tz->trips.critical.temperature);
+ tz->trips.critical.temperature,
+ tz->kelvin_offset);
return 0;
}
trip--;
@@ -711,7 +713,8 @@
if (tz->trips.hot.flags.valid) {
if (!trip) {
*temp = KELVIN_TO_MILLICELSIUS(
- tz->trips.hot.temperature);
+ tz->trips.hot.temperature,
+ tz->kelvin_offset);
return 0;
}
trip--;
@@ -720,7 +723,8 @@
if (tz->trips.passive.flags.valid) {
if (!trip) {
*temp = KELVIN_TO_MILLICELSIUS(
- tz->trips.passive.temperature);
+ tz->trips.passive.temperature,
+ tz->kelvin_offset);
return 0;
}
trip--;
@@ -730,7 +734,8 @@
tz->trips.active[i].flags.valid; i++) {
if (!trip) {
*temp = KELVIN_TO_MILLICELSIUS(
- tz->trips.active[i].temperature);
+ tz->trips.active[i].temperature,
+ tz->kelvin_offset);
return 0;
}
trip--;
@@ -745,7 +750,8 @@
if (tz->trips.critical.flags.valid) {
*temperature = KELVIN_TO_MILLICELSIUS(
- tz->trips.critical.temperature);
+ tz->trips.critical.temperature,
+ tz->kelvin_offset);
return 0;
} else
return -EINVAL;
@@ -1334,6 +1340,25 @@
return 0;
}
+/*
+ * The exact offset between Kelvin and degree Celsius is 273.15. However ACPI
+ * handles temperature values with a single decimal place. As a consequence,
+ * some implementations use an offset of 273.1 and others use an offset of
+ * 273.2. Try to find out which one is being used, to present the most
+ * accurate and visually appealing number.
+ *
+ * The heuristic below should work for all ACPI thermal zones which have a
+ * critical trip point with a value being a multiple of 0.5 degree Celsius.
+ */
+static void acpi_thermal_guess_offset(struct acpi_thermal *tz)
+{
+ if (tz->trips.critical.flags.valid &&
+ (tz->trips.critical.temperature % 5) == 1)
+ tz->kelvin_offset = 2731;
+ else
+ tz->kelvin_offset = 2732;
+}
+
static int acpi_thermal_add(struct acpi_device *device)
{
int result = 0;
@@ -1360,6 +1385,8 @@
if (result)
goto free_memory;
+ acpi_thermal_guess_offset(tz);
+
result = acpi_thermal_register_thermal_zone(tz);
if (result)
goto free_memory;
