linux-kernel - [PATCH AUTOSEL 4.9 08/45] hwmon: (ina2xx) Fix current value calculation

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Message-Id: <20181205094706.7225-8-sashal@kernel.org>
Date:   Wed,  5 Dec 2018 04:46:29 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     stable@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Nicolin Chen <nicoleotsuka@...il.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Sasha Levin <sashal@...nel.org>, linux-hwmon@...r.kernel.org
Subject: [PATCH AUTOSEL 4.9 08/45] hwmon: (ina2xx) Fix current value calculation

From: Nicolin Chen <nicoleotsuka@...il.com>

[ Upstream commit 38cd989ee38c16388cde89db5b734f9d55b905f9 ]

The current register (04h) has a sign bit at MSB. The comments
for this calculation also mention that it's a signed register.

However, the regval is unsigned type so result of calculation
turns out to be an incorrect value when current is negative.

This patch simply fixes this by adding a casting to s16.

Fixes: 5d389b125186c ("hwmon: (ina2xx) Make calibration register value fixed")
Signed-off-by: Nicolin Chen <nicoleotsuka@...il.com>
Signed-off-by: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/hwmon/ina2xx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hwmon/ina2xx.c b/drivers/hwmon/ina2xx.c
index 9ac6e1673375..1f291b344178 100644
--- a/drivers/hwmon/ina2xx.c
+++ b/drivers/hwmon/ina2xx.c
@@ -273,7 +273,7 @@ static int ina2xx_get_value(struct ina2xx_data *data, u8 reg,
 		break;
 	case INA2XX_CURRENT:
 		/* signed register, result in mA */
-		val = regval * data->current_lsb_uA;
+		val = (s16)regval * data->current_lsb_uA;
 		val = DIV_ROUND_CLOSEST(val, 1000);
 		break;
 	case INA2XX_CALIBRATION:
-- 
2.17.1