linux-kernel - [PATCH 4.9 38/57] hwmon: (tmp421) fix rounding for negative values

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Message-Id: <20211004125030.143735285@linuxfoundation.org>
Date:   Mon,  4 Oct 2021 14:52:22 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Paul Fertser <fercerpav@...il.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 38/57] hwmon: (tmp421) fix rounding for negative values

From: Paul Fertser <fercerpav@...il.com>

[ Upstream commit 724e8af85854c4d3401313b6dd7d79cf792d8990 ]

Old 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.

Fixes: 9410700b881f ("hwmon: Add driver for Texas Instruments TMP421/422/423 sensor chips")
Signed-off-by: Paul Fertser <fercerpav@...il.com>
Link: https://lore.kernel.org/r/20210924093011.26083-3-fercerpav@gmail.com
Signed-off-by: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 bfb98b96c781..324e7aaeb0b1 100644
--- a/drivers/hwmon/tmp421.c
+++ b/drivers/hwmon/tmp421.c
@@ -83,23 +83,17 @@ 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)
@@ -136,10 +130,8 @@ 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:
 		/*
-- 
2.33.0