All of lore.kernel.org
 help / color / mirror / Atom feed
* [lm-sensors] [PATCH 1/1] lm73: detect i2c bus errors before scnprintf()
@ 2012-12-21  9:58 Chris Verges
  2012-12-22  1:30 ` Guenter Roeck
                   ` (6 more replies)
  0 siblings, 7 replies; 8+ messages in thread
From: Chris Verges @ 2012-12-21  9:58 UTC (permalink / raw)
  To: lm-sensors

If an LM73 device does not exist on an I2C bus, attempts to communicate
with the device result in an error code returned from the i2c read/write
functions.  The current lm73 driver casts that return value from a s32
type to a s16 type, then converts it to a temperature in celsius.
Because negative temperatures are valid, it is difficult to distinguish
between an error code printed to the response buffer and a negative
temperature recorded by the sensor.

The solution is to evaluate the return value from the i2c functions
before performing any temperature calculations.  If the i2c function did
not succeed, the error code should be passed back through the virtual
file system layer instead of being printed into the response buffer.

Before:

   $ cat /sys/class/hwmon/hwmon0/device/temp1_input
   -46

After:

   $ cat /sys/class/hwmon/hwmon0/device/temp1_input
   cat: read error: No such device or address

Signed-off-by: Chris Verges <kg4ysn@gmail.com>
---
 drivers/hwmon/lm73.c |   16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/hwmon/lm73.c b/drivers/hwmon/lm73.c
index 8fa2632..7272176 100644
--- a/drivers/hwmon/lm73.c
+++ b/drivers/hwmon/lm73.c
@@ -49,6 +49,7 @@ static ssize_t set_temp(struct device *dev, struct device_attribute *da,
 	struct i2c_client *client = to_i2c_client(dev);
 	long temp;
 	short value;
+	s32 err;
 
 	int status = kstrtol(buf, 10, &temp);
 	if (status < 0)
@@ -57,8 +58,8 @@ static ssize_t set_temp(struct device *dev, struct device_attribute *da,
 	/* Write value */
 	value = (short) SENSORS_LIMIT(temp/250, (LM73_TEMP_MIN*4),
 		(LM73_TEMP_MAX*4)) << 5;
-	i2c_smbus_write_word_swapped(client, attr->index, value);
-	return count;
+	err = i2c_smbus_write_word_swapped(client, attr->index, value);
+	return (err < 0) ? err : count;
 }
 
 static ssize_t show_temp(struct device *dev, struct device_attribute *da,
@@ -66,11 +67,16 @@ static ssize_t show_temp(struct device *dev, struct device_attribute *da,
 {
 	struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
 	struct i2c_client *client = to_i2c_client(dev);
+	int temp;
+
+	s32 err = i2c_smbus_read_word_swapped(client, attr->index);
+	if (err < 0)
+		return err;
+
 	/* use integer division instead of equivalent right shift to
 	   guarantee arithmetic shift and preserve the sign */
-	int temp = ((s16) (i2c_smbus_read_word_swapped(client,
-		    attr->index))*250) / 32;
-	return sprintf(buf, "%d\n", temp);
+	temp = (((s16) err) * 250) / 32;
+	return scnprintf(buf, PAGE_SIZE, "%d\n", temp);
 }
 
 
-- 
1.7.9.5


_______________________________________________
lm-sensors mailing list
lm-sensors@lm-sensors.org
http://lists.lm-sensors.org/mailman/listinfo/lm-sensors

^ permalink raw reply related	[flat|nested] 8+ messages in thread
end of thread, other threads:[~2012-12-22 22:59 UTC | newest]

Thread overview: 8+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2012-12-21  9:58 [lm-sensors] [PATCH 1/1] lm73: detect i2c bus errors before scnprintf() Chris Verges
2012-12-22  1:30 ` Guenter Roeck
2012-12-22  1:37 ` Chris Verges
2012-12-22  6:59 ` Guenter Roeck
2012-12-22  7:37 ` Chris Verges
2012-12-22 11:07 ` Guenter Roeck
2012-12-22 21:48 ` Chris Verges
2012-12-22 22:59 ` Guenter Roeck

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.