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@gmail.com>
Reviewed-by: Marcelo Schmitt <marcelo.schmitt1@gmail.com>
Tested-by: Andrew Hepp <andrew.hepp@ahepp.dev>
Link: https://lore.kernel.org/r/20240424185913.1177127-1-dima.fedrau@gmail.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/temperature/mcp9600.c b/drivers/iio/temperature/mcp9600.c
index 46845804292bf06048a5ef5d976ffb28a83680c0..7a3eef5d5e752a2c4fec1f989311e15977f683e0 100644 (file)
--- 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;
 }