Re: [PATCH v2 4/5] thermal: stm32: improve temperature resolution

[Daniel Lezcano]

On 04/11/2019 14:30, Pascal Paillet wrote:
> Currently, the temperature is rounded by 1 or 2 degrees.
> Change the way of computing to avoid rounds.
> Also simplify the sampling time management.

Give more details about the changes in order to let us understand them.

> Signed-off-by: Pascal Paillet <p.paillet@xxxxxx>
> ---
>  drivers/thermal/st/stm_thermal.c | 58 ++++++++------------------------
>  1 file changed, 14 insertions(+), 44 deletions(-)
> 
> diff --git a/drivers/thermal/st/stm_thermal.c b/drivers/thermal/st/stm_thermal.c
> index cb72252f2800..9986716b17c1 100644
> --- a/drivers/thermal/st/stm_thermal.c
> +++ b/drivers/thermal/st/stm_thermal.c
> @@ -59,7 +59,6 @@
>  
>  /* Less significant bit position definitions */
>  #define TS1_T0_POS		16
> -#define TS1_SMP_TIME_POS	16
>  #define TS1_HITTHD_POS		16
>  #define TS1_LITTHD_POS		0
>  #define HSREF_CLK_DIV_POS	24
> @@ -83,15 +82,10 @@
>  #define ONE_MHZ			1000000
>  #define POLL_TIMEOUT		5000
>  #define STARTUP_TIME		40
> -#define TS1_T0_VAL0		30
> -#define TS1_T0_VAL1		130
> +#define TS1_T0_VAL0		30000  /* 30 celsius */
> +#define TS1_T0_VAL1		130000 /* 130 celsius */
>  #define NO_HW_TRIG		0
> -
> -/* The Thermal Framework expects millidegrees */
> -#define mcelsius(temp)		((temp) * 1000)
> -
> -/* The Sensor expects oC degrees */
> -#define celsius(temp)		((temp) / 1000)
> +#define SAMPLING_TIME		15
>  
>  struct stm_thermal_sensor {
>  	struct device *dev;
> @@ -259,27 +253,17 @@ static int stm_thermal_calculate_threshold(struct stm_thermal_sensor *sensor,
>  					   int temp, u32 *th)
>  {
>  	int freqM;
> -	u32 sampling_time;
> -
> -	/* Retrieve the number of periods to sample */
> -	sampling_time = (readl_relaxed(sensor->base + DTS_CFGR1_OFFSET) &
> -			TS1_SMP_TIME_MASK) >> TS1_SMP_TIME_POS;
>  
>  	/* Figure out the CLK_PTAT frequency for a given temperature */
> -	freqM = ((temp - sensor->t0) * sensor->ramp_coeff)
> -		 + sensor->fmt0;
> -
> -	dev_dbg(sensor->dev, "%s: freqM for threshold = %d Hz",
> -		__func__, freqM);
> +	freqM = ((temp - sensor->t0) * sensor->ramp_coeff) / 1000 +
> +		sensor->fmt0;
>  
>  	/* Figure out the threshold sample number */
> -	*th = clk_get_rate(sensor->clk);
> +	*th = clk_get_rate(sensor->clk) * SAMPLING_TIME / freqM;
>  	if (!*th)
>  		return -EINVAL;
>  
> -	*th = *th / freqM;
> -
> -	*th *= sampling_time;
> +	dev_dbg(sensor->dev, "freqM=%d Hz, threshold=0x%x", freqM, *th);
>  
>  	return 0;
>  }
> @@ -371,40 +355,26 @@ static int stm_thermal_set_trips(void *data, int low, int high)
>  static int stm_thermal_get_temp(void *data, int *temp)
>  {
>  	struct stm_thermal_sensor *sensor = data;
> -	u32 sampling_time;
> +	u32 periods;
>  	int freqM, ret;
>  
>  	if (sensor->mode != THERMAL_DEVICE_ENABLED)
>  		return -EAGAIN;
>  
> -	/* Retrieve the number of samples */
> -	ret = readl_poll_timeout(sensor->base + DTS_DR_OFFSET, freqM,
> -				 (freqM & TS1_MFREQ_MASK), STARTUP_TIME,
> -				 POLL_TIMEOUT);
> -
> +	/* Retrieve the number of periods sampled */
> +	ret = readl_relaxed_poll_timeout(sensor->base + DTS_DR_OFFSET, periods,
> +					 (periods & TS1_MFREQ_MASK),
> +					 STARTUP_TIME, POLL_TIMEOUT);
>  	if (ret)
>  		return ret;
>  
> -	if (!freqM)
> -		return -ENODATA;
> -
> -	/* Retrieve the number of periods sampled */
> -	sampling_time = (readl_relaxed(sensor->base + DTS_CFGR1_OFFSET) &
> -			TS1_SMP_TIME_MASK) >> TS1_SMP_TIME_POS;
> -
> -	/* Figure out the number of samples per period */
> -	freqM /= sampling_time;
> -
>  	/* Figure out the CLK_PTAT frequency */
> -	freqM = clk_get_rate(sensor->clk) / freqM;
> +	freqM = (clk_get_rate(sensor->clk) * SAMPLING_TIME) / periods;
>  	if (!freqM)
>  		return -EINVAL;
>  
> -	dev_dbg(sensor->dev, "%s: freqM=%d\n", __func__, freqM);
> -
>  	/* Figure out the temperature in mili celsius */
> -	*temp = mcelsius(sensor->t0 + ((freqM - sensor->fmt0) /
> -			 sensor->ramp_coeff));
> +	*temp = (freqM - sensor->fmt0) * 1000 / sensor->ramp_coeff + sensor->t0;
>  
>  	return 0;
>  }
> 


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