[PATCH v2 3/3] thermal: tsens: Fix negative temperature reporting

[Amit Kucheria]

The current code will always return 0xffffffff in case of negative
temperatures due to a bug in how the binary sign extension is being done.

Use sign_extend32() instead.

Signed-off-by: Amit Kucheria <amit.kuche...@linaro.org>
Reviewed-by: Matthias Kaehlcke <m...@chromium.org>
---
 drivers/thermal/qcom/tsens-v2.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/drivers/thermal/qcom/tsens-v2.c b/drivers/thermal/qcom/tsens-v2.c
index 908e3dcb2d5c..44da02f594ac 100644
--- a/drivers/thermal/qcom/tsens-v2.c
+++ b/drivers/thermal/qcom/tsens-v2.c
@@ -5,19 +5,20 @@
  */
 
 #include <linux/regmap.h>
+#include <linux/bitops.h>
 #include "tsens.h"
 
 #define STATUS_OFFSET          0xa0
 #define LAST_TEMP_MASK         0xfff
 #define STATUS_VALID_BIT       BIT(21)
-#define CODE_SIGN_BIT          BIT(11)
 
 static int get_temp_tsens_v2(struct tsens_device *tmdev, int id, int *temp)
 {
        struct tsens_sensor *s = &tmdev->sensor[id];
        u32 code;
        unsigned int status_reg;
-       int last_temp = 0, last_temp2 = 0, last_temp3 = 0, ret;
+       u32 last_temp = 0, last_temp2 = 0, last_temp3 = 0;
+       int ret;
 
        status_reg = tmdev->tm_offset + STATUS_OFFSET + s->hw_id * 4;
        ret = regmap_read(tmdev->map, status_reg, &code);
@@ -54,12 +55,8 @@ static int get_temp_tsens_v2(struct tsens_device *tmdev, int 
id, int *temp)
        else if (last_temp2 == last_temp3)
                last_temp = last_temp3;
 done:
-       /* Code sign bit is the sign extension for a negative value */
-       if (last_temp & CODE_SIGN_BIT)
-               last_temp |= ~CODE_SIGN_BIT;
-
-       /* Temperatures are in deciCelicius */
-       *temp = last_temp * 100;
+       /* Convert temperature from deciCelsius to milliCelsius */
+       *temp = sign_extend32(last_temp, fls(LAST_TEMP_MASK) - 1) * 100;
 
        return 0;
 }
-- 
2.17.GIT