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

[Anand Moon]

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.

Best Regards,

--
Markus Reichl

On 8 April 2015 at 23:19, Anand Moon <linux.amoon at gmail.com> 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 at roeck-us.net> 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 at roeck-us.net> 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 at gmail.com>
>>> >> > ---
>>> >> >  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 at samsung.com>
>>> >>
>>> >> BTW: I've added Guenter to CC.
>>> >>
>>> >> --
>>> >> Best regards,
>>> >>
>>> >> Lukasz Majewski
>>> >>
>>> >> Samsung R&D Institute Poland (SRPOL) | Linux Platform Group