Re: [PATCH 6/6] hwmon: pwm-fan: Update the duty cycle inorder to control the pwm-fan

[Anand Moon]

Hi Guenter,

I will do so.

-Anand Moon

On 10 April 2015 at 18:39, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> On 04/10/2015 05:59 AM, Anand Moon wrote:
>>
>> Hi Sjoerd,
>>
>> I don't much advance knowledge on internal signaling of pwm-samsung
>> module.
>>
>> So do I need to send this patch again ?
>>
>
> From the context, it seems that the fix in hwmon would only paint
> over a problem in the actual pwm driver, correct ?
>
> If you resubmit the patch I would expect you to explain this in the
> commit log.
>
> Guenter
>
>
>> -Anand Moon
>>
>>
>> On 10 April 2015 at 17:30, Sjoerd Simons <sjoerd.simons@xxxxxxxxxxxxxxx>
>> wrote:
>>>
>>> Hey Anand,
>>>
>>> On Fri, 2015-04-10 at 16:58 +0530, Anand Moon wrote:
>>>>
>>>> Hi Guenter/Lukasz,
>>>>
>>>> Earlier I send v2 version of the patch spiking this one.
>>>>
>>>> Markus Riechl came back to me with below mail.
>>>> So This patch confirms fixes the bug.
>>>>
>>>> I will send v3 version of the patch. Earlier I was in delima about the
>>>> bug.
>>>>
>>>> -Anand Moon
>>>> -------------------------------------------
>>>> Hi Anand,
>>>>
>>>> I tested your patch.
>>>>
>>>> After booting the fan is spinning despite only 44°C.
>>>>
>>>> /sys/class/thermal/cooling_device0/curstate is 0.
>>>> /sys/class/hwmon/hwmon4/pwm1 is 0
>>>>
>>>> when I echo 1 > cur_state and then echo 0 > cur_state again,
>>>> the fan switches to off and behaves as expected.
>>>>
>>>> It looks like there is a bug in initializing the pwm output
>>>> immediately after booting.
>>>
>>>
>>> The problem here will be that at boot the PWM runs at full duty. With
>>> the current exynos PWM drive if you disable the PWM it will stop pulsing
>>> but remain high if it was at 100% duty. My patch on which you depend
>>> upon fixed a race  where disabling the pwm right after changing the duty
>>> cycle (e.g. to 0%) also kept the signal high.
>>>
>>>  From looking at other PWM users at the time it seemed that most if not
>>> all always first set to duty to 0% and then disable the pwm. Which
>>> should work fine on exynos now. However iirc Thierry recently clarified
>>> that the expected result of pwm_disable is not just that the modulation
>>> stops but also that the output signal goes low, although that's not very
>>> explicit in the current pwm documentation.. The exynos PWM driver will
>>> need another fix tweak to make that true.
>>>
>>>
>>>
>>>> Best Regards,
>>>
>>>
>>>
>>>
>>>> --
>>>> Markus Reichl
>>>>
>>>> On 8 April 2015 at 23:19, Anand Moon <linux.amoon@xxxxxxxxx> wrote:
>>>>>
>>>>> Hi Guenter,
>>>>>
>>>>> Sorry my blunder mistake. Sorry for the noise.
>>>>>
>>>>> I just tested with spiking this patch and my observation and testing
>>>>> were wrong we can skip this patch.
>>>>>
>>>>> I will send an v2 patch series removing the patch 5 and patch 6.
>>>>>
>>>>> With correct dts changes.
>>>>>
>>>>> Thanks for pointing my mistake.
>>>>>
>>>>> -Anand Moon
>>>>>
>>>>> On 8 April 2015 at 22:23, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>>>>>>
>>>>>> On Wed, Apr 08, 2015 at 09:32:05PM +0530, Anand Moon wrote:
>>>>>>>
>>>>>>> Hi Guenter,
>>>>>>>
>>>>>>> Initially the board bootup the cooling level state is 0.
>>>>>>> So update the duty cycle and this power off the fan.
>>>>>>> As their is no state change the fan will not spin.
>>>>>>>
>>>>>>> Once the temperature sensor is reached to alert temperature it
>>>>>>> changes state.
>>>>>>> With the state change the fan cools the CPU and then stop's
>>>>>>>
>>>>>>> I have observed this state change with tmon utility in
>>>>>>> linux/tools/thermal/tmon/
>>>>>>>
>>>>>> Sorry, I am missing something. I still don't see what problem you are
>>>>>> fixing
>>>>>> with this patch. What behavior is wrong with the current code, and how
>>>>>> does your
>>>>>> patch fix it ?
>>>>>>
>>>>>> Guenter
>>>>>>
>>>>>>> -Anand Moon
>>>>>>>
>>>>>>> On 8 April 2015 at 21:02, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>>>>>>>>
>>>>>>>> On Wed, Apr 08, 2015 at 10:44:15AM +0200, Lukasz Majewski wrote:
>>>>>>>>>
>>>>>>>>> Hi Anand,
>>>>>>>>>
>>>>>>>>>> Below changes depend on following patch.
>>>>>>>>>> https://patchwork.kernel.org/patch/5944061/
>>>>>>>>>>
>>>>>>>>>> Update the pwm_config with duty then update the pwm_disable
>>>>>>>>>> to poweroff the cpu fan.
>>>>>>>>>>
>>>>>>>>
>>>>>>>> Unfortunately, the patch does not include an explanation why it is
>>>>>>>> needed.
>>>>>>>>
>>>>>>>> The original code presumably did not update the duty cycle because
>>>>>>>> pwm was about to be disabled anyway. That kind of made sense to me.
>>>>>>>> Updating the duty cycle to 0 just to disable the pwm channel right
>>>>>>>> afterwards does not immediately make sense.
>>>>>>>>
>>>>>>>> Given that, I would expect to see a rationale here. Why is this
>>>>>>>> patch needed ?
>>>>>>>> Does it fix a bug ? If yes, pelase describe the bug. If not, what is
>>>>>>>> the
>>>>>>>> purpose of this patch ?
>>>>>>>>
>>>>>>>> Maybe that is all explained in patch 0/6, which I was not copied on.
>>>>>>>> Even
>>>>>>>> if so, the reationale will be needed in the changelog to explain to
>>>>>>>> future
>>>>>>>> developers why this change was made.
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Guenter
>>>>>>>>
>>>>>>>>>> Tested on OdroidXU3 board.
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: Anand Moon <linux.amoon@xxxxxxxxx>
>>>>>>>>>> ---
>>>>>>>>>>   drivers/hwmon/pwm-fan.c | 10 ++++------
>>>>>>>>>>   1 file changed, 4 insertions(+), 6 deletions(-)
>>>>>>>>>>
>>>>>>>>>> diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
>>>>>>>>>> index 7c83dc4..f25c841 100644
>>>>>>>>>> --- a/drivers/hwmon/pwm-fan.c
>>>>>>>>>> +++ b/drivers/hwmon/pwm-fan.c
>>>>>>>>>> @@ -44,26 +44,24 @@ static int  __set_pwm(struct pwm_fan_ctx *ctx,
>>>>>>>>>> unsigned long pwm) int ret = 0;
>>>>>>>>>>
>>>>>>>>>>      mutex_lock(&ctx->lock);
>>>>>>>>>> +
>>>>>>>>
>>>>>>>>
>>>>>>>> [ please refrain from unnecessary whitespace changes ]
>>>>>>>>
>>>>>>>>>>      if (ctx->pwm_value == pwm)
>>>>>>>>>>              goto exit_set_pwm_err;
>>>>>>>>>>
>>>>>>>>>> -   if (pwm == 0) {
>>>>>>>>>> -           pwm_disable(ctx->pwm);
>>>>>>>>>> -           goto exit_set_pwm;
>>>>>>>>>> -   }
>>>>>>>>>> -
>>>>>>>>>>      duty = DIV_ROUND_UP(pwm * (ctx->pwm->period - 1), MAX_PWM);
>>>>>>>>>>      ret = pwm_config(ctx->pwm, duty, ctx->pwm->period);
>>>>>>>>>>      if (ret)
>>>>>>>>>>              goto exit_set_pwm_err;
>>>>>>>>>>
>>>>>>>>>> +   if (pwm == 0)
>>>>>>>>>> +           pwm_disable(ctx->pwm);
>>>>>>>>>> +
>>>>>>>>>>      if (ctx->pwm_value == 0) {
>>>>>>>>>>              ret = pwm_enable(ctx->pwm);
>>>>>>>>>>              if (ret)
>>>>>>>>>>                      goto exit_set_pwm_err;
>>>>>>>>>>      }
>>>>>>>>>>
>>>>>>>>>> -exit_set_pwm:
>>>>>>>>>>      ctx->pwm_value = pwm;
>>>>>>>>>>   exit_set_pwm_err:
>>>>>>>>>>      mutex_unlock(&ctx->lock);
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Reviewed-by: Lukasz Majewski <l.majewski@xxxxxxxxxxx>
>>>>>>>>>
>>>>>>>>> BTW: I've added Guenter to CC.
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> Best regards,
>>>>>>>>>
>>>>>>>>> Lukasz Majewski
>>>>>>>>>
>>>>>>>>> Samsung R&D Institute Poland (SRPOL) | Linux Platform Group
>>>
>>>
>>>
>>
>
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