hwmon: (adt7475) Make volt2reg return same reg as reg2volt input

commit cf3ca1877574a306c0207cbf7fdf25419d9229df upstream.

reg2volt returns the voltage that matches a given register value.
Converting this back the other way with volt2reg didn't return the same
register value because it used truncation instead of rounding.

This meant that values read from sysfs could not be written back to sysfs
to set back the same register value.

With this change, volt2reg will return the same value for every voltage
previously returned by reg2volt (for the set of possible input values)

Signed-off-by: Luuk Paulussen <luuk.paulussen@alliedtelesis.co.nz>
Link: https://lore.kernel.org/r/20191205231659.1301-1-luuk.paulussen@alliedtelesis.co.nz
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/hwmon/adt7475.c b/drivers/hwmon/adt7475.c
index 3cefd1aeb24f4a6c73f4bffd64fe7fc5b1edea18..1b9f6adcbd859a579b2912dd0bea971d36a403f3 100644 (file)
--- a/drivers/hwmon/adt7475.c
+++ b/drivers/hwmon/adt7475.c
@@ -268,9 +268,10 @@ static inline u16 volt2reg(int channel, long volt, u8 bypass_attn)
        long reg;
 
        if (bypass_attn & (1 << channel))
-               reg = (volt * 1024) / 2250;
+               reg = DIV_ROUND_CLOSEST(volt * 1024, 2250);
        else
-               reg = (volt * r[1] * 1024) / ((r[0] + r[1]) * 2250);
+               reg = DIV_ROUND_CLOSEST(volt * r[1] * 1024,
+                                       (r[0] + r[1]) * 2250);
        return clamp_val(reg, 0, 1023) & (0xff << 2);
 }