On 07/31/2014 12:30 AM, Axel Lin wrote:
On platforms with sizeof(int) < sizeof(long), writing a temperature
limit larger than MAXINT will result in unpredictable limit values
written to the chip.
Clamp the input values to the supported limits first to fix the problem.
Signed-off-by: Axel Lin <axel.lin@xxxxxxxxxx>
---
drivers/hwmon/lm77.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/hwmon/lm77.c b/drivers/hwmon/lm77.c
index 5ceb443..72a02b0 100644
--- a/drivers/hwmon/lm77.c
+++ b/drivers/hwmon/lm77.c
@@ -80,8 +80,7 @@ struct lm77_data {
*/
static inline s16 LM77_TEMP_TO_REG(int temp)
{
- int ntemp = clamp_val(temp, LM77_TEMP_MIN, LM77_TEMP_MAX);
- return (ntemp / 500) * 8;
+ return (temp / 500) * 8;
}
static inline int LM77_TEMP_FROM_REG(s16 reg)
@@ -176,7 +175,7 @@ static ssize_t set_temp(struct device *dev, struct device_attribute *devattr,
return err;
mutex_lock(&data->update_lock);
- data->temp[nr] = val;
+ data->temp[nr] = clamp_val(val, LM77_TEMP_MIN, LM77_TEMP_MAX);
lm77_write_value(client, temp_regs[nr], LM77_TEMP_TO_REG(val));
mutex_unlock(&data->update_lock);
return count;
@@ -199,6 +198,7 @@ static ssize_t set_temp_hyst(struct device *dev,
if (err)
return err;
+ val = clamp_val(val, LM77_TEMP_MIN, LM77_TEMP_MAX);
Unfortunately that doesn't work, for a number of reasons.
First, the temperature is read as unsigned and stored in an unsigned long.
This is wrong; nothing in the datasheet suggests that the value (the absolute
temperature) must be positive.
Second, the value written into the register is actually based on ...
mutex_lock(&data->update_lock);
data->temp[t_hyst] = data->temp[t_crit] - val;
"data->temp[t_crit] - val", so applying the clamp on val won't help since
the final value can still be out of range. Changing the code to use
long / kstrtol and to
val = clamp_val(data->temp[t_crit] - val, LM77_TEMP_MIN, LM77_TEMP_MAX);
data->temp[t_hyst] = val;
solved the problem and made my test happy.
Unfortunately, there is yet another problem: The cached value after a write and
the temperature read back from the chip after the cache expires do not match.
Specifically, writing a large value as limit returns 125000 initially,
but 1696000 (!) after the cache expires. Right now I have no idea how that happens.
Unfortunately I won't have time to track it down before early next week.
Thanks,
Guenter
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