* Re: [lm-sensors] [PATCH v2 1/2] hwmon: (lm77) Prevent overflow problem when writing large limits
2014-07-31 7:30 [lm-sensors] [PATCH v2 1/2] hwmon: (lm77) Prevent overflow problem when writing large limits Axel Lin
@ 2014-07-31 14:29 ` Guenter Roeck
2014-07-31 14:46 ` Guenter Roeck
2014-07-31 14:49 ` Axel Lin
2 siblings, 0 replies; 4+ messages in thread
From: Guenter Roeck @ 2014-07-31 14:29 UTC (permalink / raw)
To: lm-sensors
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@ingics.com>
> ---
> 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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^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [lm-sensors] [PATCH v2 1/2] hwmon: (lm77) Prevent overflow problem when writing large limits
2014-07-31 7:30 [lm-sensors] [PATCH v2 1/2] hwmon: (lm77) Prevent overflow problem when writing large limits Axel Lin
2014-07-31 14:29 ` Guenter Roeck
@ 2014-07-31 14:46 ` Guenter Roeck
2014-07-31 14:49 ` Axel Lin
2 siblings, 0 replies; 4+ messages in thread
From: Guenter Roeck @ 2014-07-31 14:46 UTC (permalink / raw)
To: lm-sensors
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@ingics.com>
> ---
> 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));
Found it: Clamp applied to data->temp[nr], but you are still using val here.
Has to be LM77_TEMP_TO_REG(data->temp[nr]).
Guenter
> 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);
> mutex_lock(&data->update_lock);
> data->temp[t_hyst] = data->temp[t_crit] - val;
> lm77_write_value(client, LM77_REG_TEMP_HYST,
>
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^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [lm-sensors] [PATCH v2 1/2] hwmon: (lm77) Prevent overflow problem when writing large limits
2014-07-31 7:30 [lm-sensors] [PATCH v2 1/2] hwmon: (lm77) Prevent overflow problem when writing large limits Axel Lin
2014-07-31 14:29 ` Guenter Roeck
2014-07-31 14:46 ` Guenter Roeck
@ 2014-07-31 14:49 ` Axel Lin
2 siblings, 0 replies; 4+ messages in thread
From: Axel Lin @ 2014-07-31 14:49 UTC (permalink / raw)
To: lm-sensors
2014-07-31 22:46 GMT+08:00 Guenter Roeck <linux@roeck-us.net>:
> 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@ingics.com>
>> ---
>> 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));
>
>
> Found it: Clamp applied to data->temp[nr], but you are still using val here.
> Has to be LM77_TEMP_TO_REG(data->temp[nr]).
Thanks a lot.
I'll send a v3 soon.
Regards,
Axel
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^ permalink raw reply [flat|nested] 4+ messages in thread