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ACPI: Adjust Kelvin offset to match local implementation
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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>
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Jean Delvare authored and Len Brown committed Apr 7, 2009
1 parent d508afb commit 13614e3
Showing 1 changed file with 34 additions and 7 deletions.
41 changes: 34 additions & 7 deletions drivers/acpi/thermal.c
Original file line number Diff line number Diff line change
Expand Up @@ -192,6 +192,7 @@ struct acpi_thermal {
struct acpi_handle_list devices;
struct thermal_zone_device *thermal_zone;
int tz_enabled;
int kelvin_offset;
struct mutex lock;
};

Expand Down Expand Up @@ -581,7 +582,7 @@ static void acpi_thermal_check(void *data)
}

/* 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)
Expand All @@ -596,7 +597,7 @@ static int thermal_get_temp(struct thermal_zone_device *thermal,
if (result)
return result;

*temp = KELVIN_TO_MILLICELSIUS(tz->temperature);
*temp = KELVIN_TO_MILLICELSIUS(tz->temperature, tz->kelvin_offset);
return 0;
}

Expand Down Expand Up @@ -702,7 +703,8 @@ static int thermal_get_trip_temp(struct thermal_zone_device *thermal,
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--;
Expand All @@ -711,7 +713,8 @@ static int thermal_get_trip_temp(struct thermal_zone_device *thermal,
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--;
Expand All @@ -720,7 +723,8 @@ static int thermal_get_trip_temp(struct thermal_zone_device *thermal,
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--;
Expand All @@ -730,7 +734,8 @@ static int thermal_get_trip_temp(struct thermal_zone_device *thermal,
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--;
Expand All @@ -745,7 +750,8 @@ static int thermal_get_crit_temp(struct thermal_zone_device *thermal,

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;
Expand Down Expand Up @@ -1334,6 +1340,25 @@ static int acpi_thermal_get_info(struct acpi_thermal *tz)
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;
Expand All @@ -1360,6 +1385,8 @@ static int acpi_thermal_add(struct acpi_device *device)
if (result)
goto free_memory;

acpi_thermal_guess_offset(tz);

result = acpi_thermal_register_thermal_zone(tz);
if (result)
goto free_memory;
Expand Down

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