thermal: stm32: Improve temperature computing

Change the way of computing to avoid rounds by 1 or 2 degrees.
Also simplify the sampling time management that is hard-coded
to maximum value during probe.

Signed-off-by: Pascal Paillet <p.paillet@st.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20200110101605.24984-6-p.paillet@st.com

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;
@@ -280,27 +274,17 @@ 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;
 }
@@ -368,40 +352,26 @@ 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;
 }