linux-kernel - [PATCH v2] hwmon: (adt7475) Make volt2reg return same reg as reg2volt input

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Message-Id: <20191205231659.1301-1-luuk.paulussen@alliedtelesis.co.nz>
Date:   Fri,  6 Dec 2019 12:16:59 +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 v2] 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>
---
 changes in v2:
 - remove unnecessary braces.
 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..01c2eeb02aa9 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