MLK-10827 imx: mx6 update 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.

Old Equation:
Temp = Troom,cal – slope*(Count measured – Count room fuse)
Where
Troom,cal = 25C  and
Slope = 0.4297157 – (0.0015974 * Count room fuse)

New Equation:
Temp = Troom,cal – slope*(Count measured – Count room fuse) +offset
Where
Troom,cal = 25C  and
Slope = 0.4445388 – (0.0016549 * Count room fuse)
Offset = 3.580661
"

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@freescale.com>

1 files changed, 21 insertions, 17 deletions

diff --git a/drivers/thermal/imx_thermal.c b/drivers/thermal/imx_thermal.c
index 3e794c7..3fb23c2 100644
--- a/drivers/thermal/imx_thermal.c
+++ b/drivers/thermal/imx_thermal.c
@@ -1,5 +1,5 @@
 /*
- * (C) Copyright 2014 Freescale Semiconductor, Inc.
+ * (C) Copyright 2014-2015 Freescale Semiconductor, Inc.
  * Author: Nitin Garg <nitin.garg@freescale.com>
  *             Ye Li <Ye.Li@freescale.com>
  *
@@ -23,8 +23,9 @@
 #define TEMPERATURE_HOT		80
 #define TEMPERATURE_MAX		125
 #define FACTOR0			10000000
-#define FACTOR1			15976
-#define FACTOR2			4297157
+#define FACTOR1			16549
+#define FACTOR2			4445388
+#define OFFSET			3580661
 #define MEASURE_FREQ		327
 
 #define TEMPSENSE0_TEMP_CNT_SHIFT	8
@@ -44,39 +45,42 @@ static int read_cpu_temperature(struct udevice *dev)
 	unsigned int *priv = dev_get_priv(dev);
 	u32 fuse = *priv;
 	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
+	 * offset = 3.580661
+	 * offset = OFFSET / 1000000
 	 * (Nmeas - n1) / (Tmeas - t1) = 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) / 1000000 + 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
@@ -108,8 +112,8 @@ static int read_cpu_temperature(struct udevice *dev)
 		>> TEMPSENSE0_TEMP_CNT_SHIFT;
 	writel(TEMPSENSE0_FINISHED, &anatop->tempsense0_clr);
 
-	/* milli_Tmeas = c2 - Nmeas * c1 */
-	temperature = (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);