On Fri, Aug 26, 2011 at 9:46 PM, Guenter Roeck
<guenter.roeck@xxxxxxxxxxxx> wrote:
> On Fri, 2011-08-26 at 07:17 -0400, J, KEERTHY wrote:
>> On Thu, Aug 25, 2011 at 9:26 PM, Guenter Roeck
>> <guenter.roeck@xxxxxxxxxxxx> wrote:
>> > On Thu, 2011-08-25 at 10:06 -0400, Guenter Roeck wrote:
>> >> On Thu, Aug 25, 2011 at 06:30:07AM -0400, J, KEERTHY wrote:
>> >> > On Wed, Aug 24, 2011 at 10:46 PM, Guenter Roeck
>> >> > <guenter.roeck@xxxxxxxxxxxx> wrote:
>> >> > > On Wed, Aug 24, 2011 at 10:37:12AM -0400, Keerthy wrote:
>> >> > >> On chip temperature sensor driver. The driver monitors the temperature of
>> >> > >> the MPU subsystem of the OMAP4. It sends notifications to the user space if
>> >> > >> the temperature crosses user defined thresholds via kobject_uevent interface.
>> >> > >> The user is allowed to configure the temperature thresholds vis sysfs nodes
>> >> > >> exposed using hwmon interface.
>> >> > >>
>> >> > >> Signed-off-by: Keerthy <j-keerthy@xxxxxx>
>> >> > >> Cc: Jean Delvare <khali@xxxxxxxxxxxx>
>> >> > >> Cc: Guenter Roeck <guenter.roeck@xxxxxxxxxxxx>
>> >> > >> Cc: lm-sensors@xxxxxxxxxxxxxx
>> >> > >
>> >
>> > [ ... ]
>> >
>> >
>> >> >
>> >> > >
>> >> > >> + }
>> >> > >> +
>> >> > >> + mutex_lock(&temp_sensor->sensor_mutex);
>> >> > >> + /* obtain the T cold value */
>> >> > >> + t_cold = omap_temp_sensor_readl(temp_sensor,
>> >> > >> + temp_sensor->registers->bgap_threshold);
>> >> > >> + t_cold = (t_cold & temp_sensor->registers->threshold_tcold_mask) >>
>> >> > >> + __ffs(temp_sensor->registers->threshold_tcold_mask);
>> >> > >> +
>> >> > >> + if (t_hot < t_cold) {
>> >> > >> + count = -EINVAL;
>> >> > >> + goto out;
>> >> > >
>> >> > > Context specific limitations like this one are not a good idea, since it assumes an order of changing max
>> >> > > and max_hysteresis which is not necessarily guaranteed by the application making the change, nor is a
>> >> > > change order order well defined or even possible. Applications should not have to bother about this.
>> >> >
>> >> > The hardware behavior is like this. As long as the temperature is below
>> >> > t_hot no interrupts are fired. Once the temperature increases above
>> >> > t_hot we get an
>> >> > interrupt. In order to avoid repeated interrupts we mask the t_hot interrupt
>> >> > in the interrupt handler and enable the t_cold interrupts. So we get a t_cold
>> >> > interrupt only when the temperature drops below the t_cold value. Hence
>> >> > setting the t_cold higher than t_hot will mess up the state machine.
>> >> >
>> >> > t_hot value should be greater than t_cold value.
>> >> >
>> >> One option would be to update t_cold (max_hyst) automatically in that case.
>> >>
>> >> Problem here is that you expect the application to know, depending on the current
>> >> values of (max, max_hyst), how to update both limits in order. That is not a reasonable
>> >> expectation.
>> >>
>> > One possible solution would be to have a single function to set both
>> > t_cold and t_hot, and call it from both initialization code and from the
>> > set functions. That would unify all the register setting and interrupt
>> > enable code.
>> >
>> > Regarding the actual values to set, you can (as an example) use the
>> > following approach:
>> >
>> > - If max is set, and t_hot < t_cold, adjust t_cold to the new value of
>> > t_hot.
>> >
>> > - if max_hyst is set, and t_cold > t_hot, set t_cold to the new value of
>> > t_hot.
>> >
>> > So, in other words, your new unified function would only need the
>> > following simple validation:
>> >
>> > if (t_cold > t_hot)
>> > t_cold = t_hot;
>>
>> One concern here. There should be a hysteresis
>> difference between the two and can not be equal.
>> I need to add a hysteresis value to t_hot so as
>> to maintain t_hot > t_cold condition.
>>
> Sure, makes sense. Was that in your original patch ? Just wondering.
Original patch never let the user set thresholds which failed to
satisfy the condition t_hot > t_cold. The original patch threw up
error if this condition was violated.
>
> Thanks,
> Guenter
>
>
>
--
Regards and Thanks,
Keerthy
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