thermal: imx: update to new formula according to NXP AN5215
According to an application note from 03/2017 there is an updated formula to
calculate the temperature that better matches reality. This is implemented here.
While updating move the magic constants from cpp defines which are far above the
explaining formula to constants in the code just under the explaining comment.
Reviewed-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>
diff --git a/drivers/thermal/imx_thermal.c b/drivers/thermal/imx_thermal.c
index 41e15cf..a67781b 100644
--- a/drivers/thermal/imx_thermal.c
+++ b/drivers/thermal/imx_thermal.c
@@ -70,10 +70,6 @@
#define IMX_POLLING_DELAY 2000 /* millisecond */
#define IMX_PASSIVE_DELAY 1000
-#define FACTOR0 10000000
-#define FACTOR1 15976
-#define FACTOR2 4297157
-
#define TEMPMON_IMX6Q 1
#define TEMPMON_IMX6SX 2
@@ -350,7 +346,7 @@
static int imx_init_calib(struct platform_device *pdev, u32 ocotp_ana1)
{
struct imx_thermal_data *data = platform_get_drvdata(pdev);
- int t1, n1;
+ int n1;
u64 temp64;
if (ocotp_ana1 == 0 || ocotp_ana1 == ~0) {
@@ -365,25 +361,25 @@
* To find the actual temperature T, the following formula has to be used
* when reading value n from the sensor:
*
- * T = T1 + (N - N1) / (0.4297157 - 0.0015976 * N1) °C
- * = [T1 - N1 / (0.4297157 - 0.0015976 * N1) °C] + N / (0.4297157 - 0.0015976 * N1) °C
- * = [T1 + N1 / (0.0015976 * N1 - 0.4297157) °C] - N / (0.0015976 * N1 - 0.4297157) °C
+ * T = T1 + (N - N1) / (0.4148468 - 0.0015423 * N1) °C + 3.580661 °C
+ * = [T1' - N1 / (0.4148468 - 0.0015423 * N1) °C] + N / (0.4148468 - 0.0015423 * N1) °C
+ * = [T1' + N1 / (0.0015423 * N1 - 0.4148468) °C] - N / (0.0015423 * N1 - 0.4148468) °C
* = c2 - c1 * N
*
* with
*
- * c1 = 1 / (0.0015976 * N1 - 0.4297157) °C
- * c2 = T1 + N1 / (0.0015976 * N1 - 0.4297157) °C
- * = T1 + N1 * C1
+ * T1' = 28.580661 °C
+ * c1 = 1 / (0.0015423 * N1 - 0.4297157) °C
+ * c2 = T1' + N1 / (0.0015423 * N1 - 0.4148468) °C
+ * = T1' + N1 * c1
*/
n1 = ocotp_ana1 >> 20;
- t1 = 25; /* °C */
- temp64 = FACTOR0; /* 10^7 for FACTOR1 and FACTOR2 */
+ temp64 = 10000000; /* use 10^7 as fixed point constant for values in formula */
temp64 *= 1000; /* to get result in °mC */
- do_div(temp64, FACTOR1 * n1 - FACTOR2);
+ do_div(temp64, 15423 * n1 - 4148468);
data->c1 = temp64;
- data->c2 = n1 * data->c1 + 1000 * t1;
+ data->c2 = n1 * data->c1 + 28581;
return 0;
}