linux-kernel - [PATCH] iio: temperature: mcp9600: Fix temperature reading for negative values

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Date: Wed, 24 Apr 2024 20:59:10 +0200
From: Dimitri Fedrau <dima.fedrau@...il.com>
To: 
Cc: Dimitri Fedrau <dima.fedrau@...il.com>,
	Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Andrew Hepp <andrew.hepp@...pp.dev>,
	linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] iio: temperature: mcp9600: Fix temperature reading for negative values

Temperature is stored as 16bit value in two's complement format. Current
implementation ignores the sign bit. Make it aware of the sign bit by
using sign_extend32.

Fixes: 3f6b9598b6df ("iio: temperature: Add MCP9600 thermocouple EMF converter")
Signed-off-by: Dimitri Fedrau <dima.fedrau@...il.com>
---
 drivers/iio/temperature/mcp9600.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/temperature/mcp9600.c b/drivers/iio/temperature/mcp9600.c
index 46845804292b..7a3eef5d5e75 100644
--- a/drivers/iio/temperature/mcp9600.c
+++ b/drivers/iio/temperature/mcp9600.c
@@ -52,7 +52,8 @@ static int mcp9600_read(struct mcp9600_data *data,
 
 	if (ret < 0)
 		return ret;
-	*val = ret;
+
+	*val = sign_extend32(ret, 15);
 
 	return 0;
 }
-- 
2.39.2