imx: thermal: update imx6 thermal driver according new equation

>From IC guys:
"
After a thorough accuracy study of the Temp sense circuit,
we found that with our current equation, an average part can
read 7 degrees lower than a known forced temperature.
We also found out that the standard variance was around 2C;
which is the tightest distribution that we could create.
We need to change the temp sense equation to center the average
part around the target temperature.
"

New equation:
Tmeas = (Nmeas - n1) / slope + t1 + offset
n1= fused room count
t1= 25
offset=3.580661
slope= 0.4148468 – 0.0015423*n1

According the new equation, update the thermal driver.
c1 and c2 changed to u64 type and update comments.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>

diff --git a/drivers/thermal/imx_thermal.c b/drivers/thermal/imx_thermal.c
index 05090945550542fedb28d2a81a9fb2b21a2137ae..b159464d82e79499e035df75d6a16866f62c19da 100644 (file)
--- a/drivers/thermal/imx_thermal.c
+++ b/drivers/thermal/imx_thermal.c
@@ -22,8 +22,9 @@
 /* board will busyloop until this many degrees C below CPU max temperature */
 #define TEMPERATURE_HOT_DELTA   5 /* CPU maxT - 5C */
 #define FACTOR0                        10000000
-#define FACTOR1                        15976
-#define FACTOR2                        4297157
+#define FACTOR1                        15423
+#define FACTOR2                        4148468
+#define OFFSET                 3580661
 #define MEASURE_FREQ           327
 #define TEMPERATURE_MIN         -40
 #define TEMPERATURE_HOT         85
@@ -54,39 +55,42 @@ static int read_cpu_temperature(struct udevice *dev)
        struct thermal_data *priv = dev_get_priv(dev);
        u32 fuse = priv->fuse;
        int t1, n1;
-       u32 c1, c2;
+       u64 c1, c2;
        u64 temp64;
 
        /*
         * Sensor data layout:
         *   [31:20] - sensor value @ 25C
         * We use universal formula now and only need sensor value @ 25C
-        * slope = 0.4297157 - (0.0015976 * 25C fuse)
+        * slope = 0.4445388 - (0.0016549 * 25C fuse)
         */
        n1 = fuse >> 20;
        t1 = 25; /* t1 always 25C */
 
        /*
         * Derived from linear interpolation:
-        * slope = 0.4297157 - (0.0015976 * 25C fuse)
+        * slope = 0.4445388 - (0.0016549 * 25C fuse)
         * slope = (FACTOR2 - FACTOR1 * n1) / FACTOR0
-        * (Nmeas - n1) / (Tmeas - t1) = slope
+        * offset = 3.580661
+        * offset = OFFSET / 1000000
+        * (Nmeas - n1) / (Tmeas - t1 - offset) = slope
         * We want to reduce this down to the minimum computation necessary
         * for each temperature read.  Also, we want Tmeas in millicelsius
         * and we don't want to lose precision from integer division. So...
-        * Tmeas = (Nmeas - n1) / slope + t1
-        * milli_Tmeas = 1000 * (Nmeas - n1) / slope + 1000 * t1
-        * milli_Tmeas = -1000 * (n1 - Nmeas) / slope + 1000 * t1
-        * Let constant c1 = (-1000 / slope)
-        * milli_Tmeas = (n1 - Nmeas) * c1 + 1000 * t1
-        * Let constant c2 = n1 *c1 + 1000 * t1
-        * milli_Tmeas = c2 - Nmeas * c1
+        * Tmeas = (Nmeas - n1) / slope + t1 + offset
+        * milli_Tmeas = 1000000 * (Nmeas - n1) / slope + 1000000 * t1 + OFFSET
+        * milli_Tmeas = -1000000 * (n1 - Nmeas) / slope + 1000000 * t1 + OFFSET
+        * Let constant c1 = (-1000000 / slope)
+        * milli_Tmeas = (n1 - Nmeas) * c1 + 1000000 * t1 + OFFSET
+        * Let constant c2 = n1 *c1 + 1000000 * t1
+        * milli_Tmeas = (c2 - Nmeas * c1) + OFFSET
+        * Tmeas = ((c2 - Nmeas * c1) + OFFSET) / 1000000
         */
        temp64 = FACTOR0;
-       temp64 *= 1000;
+       temp64 *= 1000000;
        do_div(temp64, FACTOR1 * n1 - FACTOR2);
        c1 = temp64;
-       c2 = n1 * c1 + 1000 * t1;
+       c2 = n1 * c1 + 1000000 * t1;
 
        /*
         * now we only use single measure, every time we read
@@ -118,8 +122,8 @@ static int read_cpu_temperature(struct udevice *dev)
                >> TEMPSENSE0_TEMP_CNT_SHIFT;
        writel(TEMPSENSE0_FINISHED, &anatop->tempsense0_clr);
 
-       /* milli_Tmeas = c2 - Nmeas * c1 */
-       temperature = (long)(c2 - n_meas * c1)/1000;
+       /* Tmeas = (c2 - Nmeas * c1 + OFFSET) / 1000000 */
+       temperature = lldiv(c2 - n_meas * c1 + OFFSET, 1000000);
 
        /* power down anatop thermal sensor */
        writel(TEMPSENSE0_POWER_DOWN, &anatop->tempsense0_set);