thermal: kirkwood: Fix thermal sensor formula

The currently formula has been taken from the 88AP510 SoC datasheet,
which is not exactly correct. The correct value for the temperature
in Celcius of the sensor present in this SoC is:

  Celsius = (322-reg)/1.3625

Signed-off-by: Lior Amsalem <alior@marvell.com>
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>

diff --git a/drivers/thermal/kirkwood_thermal.c b/drivers/thermal/kirkwood_thermal.c
index d2e05ee..dfeceaf 100644 (file)
--- a/drivers/thermal/kirkwood_thermal.c
+++ b/drivers/thermal/kirkwood_thermal.c
@@ -49,13 +49,13 @@ static int kirkwood_get_temp(struct thermal_zone_device *thermal,
        }
 
        /*
-        * Calculate temperature. See Section 8.10.1 of the 88AP510,
-        * datasheet, which has the same sensor.
-        * Documentation/arm/Marvell/README
+        * Calculate temperature. According to Marvell internal
+        * documentation the formula for this is:
+        * Celsius = (322-reg)/1.3625
         */
        reg = (reg >> KIRKWOOD_THERMAL_TEMP_OFFSET) &
                KIRKWOOD_THERMAL_TEMP_MASK;
-       *temp = ((2281638UL - (7298*reg)) / 10);
+       *temp = ((3220000000UL - (10000000UL * reg)) / 13625);
 
        return 0;
 }