From 0602934f302e016e2ea5dc6951681bfac77455ef Mon Sep 17 00:00:00 2001 From: Chris Verges Date: Fri, 21 Dec 2012 01:58:34 -0800 Subject: [PATCH] hwmon: (lm73} Detect and report i2c bus errors 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 Cc: stable@vger.kernel.org Signed-off-by: Guenter Roeck --- 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 8fa2632cbbaf..7272176a9ec7 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); } -- 2.20.1