From dac552f4bac581b62cea1c77e2a2d8fde5ea3bc7 Mon Sep 17 00:00:00 2001 From: Anson Huang Date: Wed, 31 Jul 2013 19:29:29 -0400 Subject: [PATCH] ENGR00273344-1 thermal: imx: Update formula for thermal sensor Thermal sensor used to need two calibration data which are in Fuse to get a slope for converting thermal sensor's raw data to real temperature in degree C. Now we use an universal formula to get real temp from internal thermal sensor raw data: Slope = 0.4297157 - (0.0015976 * 25C fuse); Using universal formula can reduce the effort of chip calibration, so update the formula. Signed-off-by: Anson Huang --- drivers/thermal/imx_thermal.c | 45 +++++++++++++++++++++-------------- 1 file changed, 27 insertions(+), 18 deletions(-) diff --git a/drivers/thermal/imx_thermal.c b/drivers/thermal/imx_thermal.c index d16c33c7f3f0..8e91267fa29f 100644 --- a/drivers/thermal/imx_thermal.c +++ b/drivers/thermal/imx_thermal.c @@ -1,5 +1,5 @@ /* - * Copyright 2013 Freescale Semiconductor, Inc. + * Copyright (C) 2013 Freescale Semiconductor, Inc. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as @@ -64,12 +64,16 @@ enum imx_thermal_trip { #define IMX_POLLING_DELAY 2000 /* millisecond */ #define IMX_PASSIVE_DELAY 1000 +#define FACTOR0 10000000 +#define FACTOR1 15976 +#define FACTOR2 4297157 + struct imx_thermal_data { struct thermal_zone_device *tz; struct thermal_cooling_device *cdev; enum thermal_device_mode mode; struct regmap *tempmon; - int c1, c2; /* See formula in imx_get_sensor_data() */ + u32 c1, c2; /* See formula in imx_get_sensor_data() */ }; static int imx_get_temp(struct thermal_zone_device *tz, unsigned long *temp) @@ -106,7 +110,7 @@ static int imx_get_temp(struct thermal_zone_device *tz, unsigned long *temp) n_meas = (val & TEMPSENSE0_TEMP_CNT_MASK) >> TEMPSENSE0_TEMP_CNT_SHIFT; /* See imx_get_sensor_data() for formula derivation */ - *temp = data->c2 + data->c1 * n_meas; + *temp = data->c2 - n_meas * data->c1; if (*temp != last_temp) { dev_dbg(&tz->device, "millicelsius: %ld\n", *temp); @@ -217,9 +221,10 @@ static int imx_get_sensor_data(struct platform_device *pdev) { struct imx_thermal_data *data = platform_get_drvdata(pdev); struct regmap *map; - int t1, t2, n1, n2; + int t1, n1; int ret; u32 val; + u64 temp64; map = syscon_regmap_lookup_by_phandle(pdev->dev.of_node, "fsl,tempmon-data"); @@ -243,29 +248,33 @@ static int imx_get_sensor_data(struct platform_device *pdev) /* * Sensor data layout: * [31:20] - sensor value @ 25C - * [19:8] - sensor value of hot - * [7:0] - hot temperature value + * We use universal formula now and only need sensor value @ 25C + * slope = 0.4297157 - (0.0015976 * 25C fuse) */ n1 = val >> 20; - n2 = (val & 0xfff00) >> 8; - t2 = val & 0xff; t1 = 25; /* t1 always 25C */ /* - * Derived from linear interpolation, - * Tmeas = T2 + (Nmeas - N2) * (T1 - T2) / (N1 - N2) + * Derived from linear interpolation: + * slope = 0.4297157 - (0.0015976 * 25C fuse) + * slope = (FACTOR2 - FACTOR1 * n1) / FACTOR0 + * (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... - * milli_Tmeas = 1000 * T2 + 1000 * (Nmeas - N2) * (T1 - T2) / (N1 - N2) - * Let constant c1 = 1000 * (T1 - T2) / (N1 - N2) - * milli_Tmeas = (1000 * T2) + c1 * (Nmeas - N2) - * milli_Tmeas = (1000 * T2) + (c1 * Nmeas) - (c1 * N2) - * Let constant c2 = (1000 * T2) - (c1 * N2) - * milli_Tmeas = c2 + (c1 * Nmeas) + * 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 */ - data->c1 = 1000 * (t1 - t2) / (n1 - n2); - data->c2 = 1000 * t2 - data->c1 * n2; + temp64 = FACTOR0; + temp64 *= 1000; + do_div(temp64, FACTOR1 * n1 - FACTOR2); + data->c1 = temp64; + data->c2 = n1 * data->c1 + 1000 * t1; return 0; } -- 2.39.5