linux-kernel - [PATCH 4.4 166/183] hwmon: (adt7475) Make volt2reg return same reg as reg2volt input

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Message-Id: <20200128135846.251622556@linuxfoundation.org>
Date:   Tue, 28 Jan 2020 15:06:25 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Luuk Paulussen <luuk.paulussen@...iedtelesis.co.nz>,
        Guenter Roeck <linux@...ck-us.net>
Subject: [PATCH 4.4 166/183] hwmon: (adt7475) Make volt2reg return same reg as reg2volt input

From: Luuk Paulussen <luuk.paulussen@...iedtelesis.co.nz>

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@...iedtelesis.co.nz>
Link: https://lore.kernel.org/r/20191205231659.1301-1-luuk.paulussen@alliedtelesis.co.nz
cc: stable@...r.kernel.org
Signed-off-by: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/hwmon/adt7475.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/hwmon/adt7475.c
+++ b/drivers/hwmon/adt7475.c
@@ -268,9 +268,10 @@ static inline u16 volt2reg(int channel,
 	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);
 }