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

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
cc: stable@vger.kernel.org
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/adt7475.c b/drivers/hwmon/adt7475.c
index 6c64d50c9aae8ec175d9477fa98af6c851849d2f..01c2eeb02aa965e176eed3c0cdb8a9e393c95c63 100644 (file)
--- a/drivers/hwmon/adt7475.c
+++ b/drivers/hwmon/adt7475.c
@@ -294,9 +294,10 @@ 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);
 }