[PATCH] thermal: imx: update formula for thermal sensor

[Shawn Guo]

Copy LAKML and pengutronix folks in case they have comments.

On Wed, Feb 12, 2014 at 06:06:35PM +0800, Anson Huang wrote:
> Thermal sensor used to need two calibration points which are
> in fuse map to get a slope for converting thermal sensor's raw
> data to real temperature in degree C. Due to the chip calibration
> limitation, hardware team provides an universal formula to get
> real temperature from internal thermal sensor raw data:
> 
> Slope = 0.4297157 - (0.0015976 * 25C fuse);
> 
> Update the formula, as there will be no hot point calibration
> data in fuse map from now on.
> 
> Signed-off-by: Anson Huang <b20788 at freescale.com>

Acked-by: Shawn Guo <shawn.guo at linaro.org>

Shawn

> ---
>  drivers/thermal/imx_thermal.c |   39 ++++++++++++++++++++++++++-------------
>  1 file changed, 26 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/thermal/imx_thermal.c b/drivers/thermal/imx_thermal.c
> index 45af765..a99c631 100644
> --- a/drivers/thermal/imx_thermal.c
> +++ b/drivers/thermal/imx_thermal.c
> @@ -62,12 +62,16 @@ 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() */
>  	unsigned long temp_passive;
>  	unsigned long temp_critical;
>  	unsigned long alarm_temp;
> @@ -84,7 +88,7 @@ static void imx_set_alarm_temp(struct imx_thermal_data *data,
>  	int alarm_value;
>  
>  	data->alarm_temp = alarm_temp;
> -	alarm_value = (alarm_temp - data->c2) / data->c1;
> +	alarm_value = (data->c2 - alarm_temp) / data->c1;
>  	regmap_write(map, TEMPSENSE0 + REG_CLR, TEMPSENSE0_ALARM_VALUE_MASK);
>  	regmap_write(map, TEMPSENSE0 + REG_SET, alarm_value <<
>  			TEMPSENSE0_ALARM_VALUE_SHIFT);
> @@ -136,7 +140,7 @@ 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;
>  
>  	/* Update alarm value to next higher trip point */
>  	if (data->alarm_temp == data->temp_passive && *temp >= data->temp_passive)
> @@ -305,6 +309,7 @@ static int imx_get_sensor_data(struct platform_device *pdev)
>  	int t1, t2, n1, n2;
>  	int ret;
>  	u32 val;
> +	u64 temp64;
>  
>  	map = syscon_regmap_lookup_by_phandle(pdev->dev.of_node,
>  					      "fsl,tempmon-data");
> @@ -330,6 +335,8 @@ static int imx_get_sensor_data(struct platform_device *pdev)
>  	 *   [31:20] - sensor value @ 25C
>  	 *    [19:8] - sensor value of hot
>  	 *     [7:0] - hot temperature value
> +	 * Use universal formula now and only need sensor value @ 25C
> +	 * slope = 0.4297157 - (0.0015976 * 25C fuse)
>  	 */
>  	n1 = val >> 20;
>  	n2 = (val & 0xfff00) >> 8;
> @@ -337,20 +344,26 @@ static int imx_get_sensor_data(struct platform_device *pdev)
>  	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;
>  
>  	/*
>  	 * Set the default passive cooling trip point to 20 °C below the
> -- 
> 1.7.9.5
> 
>