linux-kernel - [PATCH 3/3] hwmon: tmp421: fix rounding for negative values

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Message-Id: <20210922134154.20766-3-fercerpav@gmail.com>
Date:   Wed, 22 Sep 2021 16:41:54 +0300
From:   Paul Fertser <fercerpav@...il.com>
To:     linux-hwmon@...r.kernel.org
Cc:     Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        linux-kernel@...r.kernel.org, Paul Fertser <fercerpav@...il.com>
Subject: [PATCH 3/3] hwmon: tmp421: fix rounding for negative values

Current code produces -24999 for 0b1110011100000000 input in standard
format due to always rounding up rather than "away from zero". Use the
common macro for division, unify and simplify the conversion code along
the way.

Signed-off-by: Paul Fertser <fercerpav@...il.com>
---
 drivers/hwmon/tmp421.c | 24 ++++++++----------------
 1 file changed, 8 insertions(+), 16 deletions(-)

diff --git a/drivers/hwmon/tmp421.c b/drivers/hwmon/tmp421.c
index 9ee4c61531f3..dec3aced3d8b 100644
--- a/drivers/hwmon/tmp421.c
+++ b/drivers/hwmon/tmp421.c
@@ -100,23 +100,17 @@ struct tmp421_data {
 	s16 temp[4];
 };
 
-static int temp_from_s16(s16 reg)
+static int temp_from_raw(u16 reg, bool extended)
 {
 	/* Mask out status bits */
 	int temp = reg & ~0xf;
 
-	return (temp * 1000 + 128) / 256;
-}
-
-static int temp_from_u16(u16 reg)
-{
-	/* Mask out status bits */
-	int temp = reg & ~0xf;
-
-	/* Add offset for extended temperature range. */
-	temp -= 64 * 256;
+	if (extended)
+		temp = temp - 64 * 256;
+	else
+		temp = (s16)temp;
 
-	return (temp * 1000 + 128) / 256;
+	return DIV_ROUND_CLOSEST(temp * 1000, 256);
 }
 
 static struct tmp421_data *tmp421_update_device(struct device *dev)
@@ -167,10 +161,8 @@ static int tmp421_read(struct device *dev, enum hwmon_sensor_types type,
 
 	switch (attr) {
 	case hwmon_temp_input:
-		if (tmp421->config & TMP421_CONFIG_RANGE)
-			*val = temp_from_u16(tmp421->temp[channel]);
-		else
-			*val = temp_from_s16(tmp421->temp[channel]);
+		*val = temp_from_raw(tmp421->temp[channel],
+				     tmp421->config & TMP421_CONFIG_RANGE);
 		return 0;
 	case hwmon_temp_fault:
 		/*
-- 
2.17.1