[PATCH v3 13/19] hwmon: (mr75203) modify the temperature equation according to series 5 datasheet

Eliav Farber
2022-08-30T19:24:22Z

Modify the equation and coefficients used to convert the digital output
to temperature according to series 5 of the Moortec Embedded Temperature
Sensor (METS) datasheet:
T = G + H * (n / cal5 - 0.5) + J * F

Where:
*) G = 60, H = 200, cal5 = 4094, J = -0.1.
*) F = frequency clock in MHz.
*) n is the digital output.

In code, the G, H and J coefficients are multiplied by a factor of 1000
to get the temperature in milli-Celsius.
Final result is clamped in case it exceeds min/max thresholds.

Change is done since it is not clear where the current equation and
coefficients came from.

Signed-off-by: Eliav Farber <farbere@amazon.com>
---
V3 -> V2:
- Protect from overflow.
- Add temperature clamping.
- Add better documentation.

drivers/hwmon/mr75203.c | 29 +++++++++++++++++++++--------
1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/drivers/hwmon/mr75203.c b/drivers/hwmon/mr75203.c
index d1f090a9baac..5b8ca1ee4a54 100644
--- a/drivers/hwmon/mr75203.c
+++ b/drivers/hwmon/mr75203.c
@@ -103,13 +103,17 @@

#define PVT_POLL_DELAY_US 20
#define PVT_POLL_TIMEOUT_US 20000
-#define PVT_H_CONST 100000
-#define PVT_CAL5_CONST 2047
-#define PVT_G_CONST 40000
+#define PVT_H_CONST 200000
+#define PVT_G_CONST 60000
+#define PVT_J_CONST -100
+#define PVT_CAL5_CONST 4094
#define PVT_CONV_BITS 10
#define PVT_N_CONST 90
#define PVT_R_CONST 245805

+#define PVT_TEMP_MIN -40000
+#define PVT_TEMP_MAX 125000
+
#define PRE_SCALER_X1 1
#define PRE_SCALER_X2 2

@@ -157,13 +161,24 @@ static umode_t pvt_is_visible(const void *data, enum hwmon_sensor_types type,
return 0;
}

+static long pvt_calc_temp(struct pvt_device *pvt, u32 nbs)
+{
+ /*
+ * Convert the register value to degrees centigrade temperature:
+ * T = G + H * (n / cal5 - 0.5) + J * F
+ */
+ s64 tmp = PVT_G_CONST + PVT_H_CONST * (s64)nbs / PVT_CAL5_CONST -
+ PVT_H_CONST / 2 + PVT_J_CONST * (s64)pvt->ip_freq / HZ_PER_MHZ;
+
+ return clamp_val(tmp, PVT_TEMP_MIN, PVT_TEMP_MAX);
+}
+
static int pvt_read_temp(struct device *dev, u32 attr, int channel, long *val)
{
struct pvt_device *pvt = dev_get_drvdata(dev);
struct regmap *t_map = pvt->t_map;
u32 stat, nbs;
int ret;
- u64 tmp;

switch (attr) {
case hwmon_temp_input:
@@ -184,9 +199,7 @@ static int pvt_read_temp(struct device *dev, u32 attr, int channel, long *val)
* Convert the register value to
* degrees centigrade temperature
*/
- tmp = nbs * PVT_H_CONST;
- do_div(tmp, PVT_CAL5_CONST);
- *val = tmp - PVT_G_CONST - pvt->ip_freq;
+ *val = pvt_calc_temp(pvt, nbs);

return 0;
default:
@@ -311,7 +324,7 @@ static int pvt_init(struct pvt_device *pvt)
(key >> 1) << CLK_SYNTH_HI_SFT |
(key >> 1) << CLK_SYNTH_HOLD_SFT | CLK_SYNTH_EN;

- pvt->ip_freq = sys_freq * 100 / (key + 2);
+ pvt->ip_freq = clk_get_rate(pvt->clk) / (key + 2);

if (t_num) {
ret = regmap_write(t_map, SDIF_SMPL_CTRL, 0x0);
--
2.37.1