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imx: thermal: update imx6 thermal driver according new equation

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>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>
This commit is contained in:
Peng Fan 2017-04-18 20:41:52 +08:00 committed by Stefano Babic
parent 2096da452b
commit 4fac417168
1 changed files with 21 additions and 17 deletions
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38
drivers/thermal/imx_thermal.c
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@ -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);