[U-Boot-Users] [PATCH] LM75 bug fix for negative temperatures

[Larry Johnson]

When the LM75 temperature sensor measures a temperature below 0 C, the
current driver does not perform sign extension, so the result returned is
256 C too high.  This patch fixes the problem.

Signed-off-by: Larry Johnson <lrj at acm.org>
---
The patch was tested on the AMCC Sequoia board, which uses the AD7414
temperature sensor.  It appears that other drivers, such as "ds1621.c",
may have the same bug, but I have no way of testing these.

 drivers/hwmon/lm75.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/drivers/hwmon/lm75.c b/drivers/hwmon/lm75.c
index 63f3b75..e29b294 100644
--- a/drivers/hwmon/lm75.c
+++ b/drivers/hwmon/lm75.c
@@ -179,7 +179,13 @@ int dtt_init (void)
 
 int dtt_get_temp(int sensor)
 {
-    return (dtt_read(sensor, DTT_READ_TEMP) / 256);
+    int const ret = dtt_read(sensor, DTT_READ_TEMP);
+
+    if (ret < 0) {
+	printf("DTT temperature read failed.\n");
+	return 0;
+    }
+    return (int)((int16_t) ret / 256);
 } /* dtt_get_temp() */
 
 #endif /* CONFIG_DTT_LM75 */