linux-kernel - [PATCH] hwmon: (adt7475) Make volt2reg return same reg as reg2volt input

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Message-Id: <20191205225430.14959-1-luuk.paulussen@alliedtelesis.co.nz>
Date:   Fri,  6 Dec 2019 11:54:30 +1300
From:   Luuk Paulussen <luuk.paulussen@...iedtelesis.co.nz>
To:     Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>
Cc:     linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
        Luuk Paulussen <luuk.paulussen@...iedtelesis.co.nz>
Subject: [PATCH] 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@...iedtelesis.co.nz>
---
 drivers/hwmon/adt7475.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/adt7475.c b/drivers/hwmon/adt7475.c
index 6c64d50c9aae..5eed7dd2f16d 100644
--- 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);
 }
 
-- 
2.24.0