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authorUwe Kleine-König <u.kleine-koenig@pengutronix.de>2017-11-30 10:17:38 +0100
committerEduardo Valentin <edubezval@gmail.com>2018-01-01 11:49:01 -0800
commit4e5f61ca11e716c2a46e163bd0286cb8950dc087 (patch)
tree08e62d9ec5e08e2ea57041dce91b56328b05a476 /drivers/thermal
parent339d7492dbfd76b7ed67366ba7c062c4fb61e560 (diff)
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>
Diffstat (limited to 'drivers/thermal')
-rw-r--r--drivers/thermal/imx_thermal.c26
1 files changed, 11 insertions, 15 deletions
diff --git a/drivers/thermal/imx_thermal.c b/drivers/thermal/imx_thermal.c
index 41e15cf5ffd7..a67781b7a0b2 100644
--- a/drivers/thermal/imx_thermal.c
+++ b/drivers/thermal/imx_thermal.c
@@ -70,10 +70,6 @@ enum imx_thermal_trip {
#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 struct thermal_zone_device_ops imx_tz_ops = {
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 @@ static int imx_init_calib(struct platform_device *pdev, u32 ocotp_ana1)
* 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;
}

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