[PATCH v3 12/19] hwmon: (mr75203) fix voltage equation for negative source input

Eliav Farber
2022-08-30T19:22:39Z

According to Moortec Embedded Voltage Monitor (MEVM) series 3 data sheet,
the minimum input signal is -100mv and maximum input signal is +1000mv.
When n was small enough, such that PVT_N_CONST * n < PVT_R_CONST it
resulted in n overflowing to a very large number (since n is u32 type).

This change fixes the problem by casting n to long and replacing shift
right with div operation.

Signed-off-by: Eliav Farber <farbere@amazon.com>
---
V3 -> V2:
- Fix equation to support negative values instead of limiting value to
zero.

drivers/hwmon/mr75203.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/mr75203.c b/drivers/hwmon/mr75203.c
index 1cd5ff6eacce..d1f090a9baac 100644
--- a/drivers/hwmon/mr75203.c
+++ b/drivers/hwmon/mr75203.c
@@ -222,10 +222,11 @@ static int pvt_read_in(struct device *dev, u32 attr, int channel, long *val)
return ret;

n &= SAMPLE_DATA_MSK;
+
/* Convert the N bitstream count into voltage */
pre_scaler = pvt->vd[channel].pre_scaler;
- *val = pre_scaler * (PVT_N_CONST * n - PVT_R_CONST) >>
- PVT_CONV_BITS;
+ *val = pre_scaler * (PVT_N_CONST * (long)n - PVT_R_CONST) /
+ (1 << PVT_CONV_BITS);

return 0;
default:
--
2.37.1