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

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Date:	Wed, 8 Apr 2015 23:19:43 +0530
From:	Anand Moon <linux.amoon@...il.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Lukasz Majewski <l.majewski@...sung.com>,
	Eduardo Valentin <edubezval@...il.com>,
	Sjoerd Simons <sjoerd.simons@...labora.co.uk>,
	Russell King <linux@....linux.org.uk>,
	Kukjin Kim <kgene@...nel.org>, devicetree@...r.kernel.org,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>, linux-pwm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 6/6] hwmon: pwm-fan: Update the duty cycle inorder to
 control the pwm-fan

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@...ck-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@...ck-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@...il.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@...sung.com>
>> >>
>> >> BTW: I've added Guenter to CC.
>> >>
>> >> --
>> >> Best regards,
>> >>
>> >> Lukasz Majewski
>> >>
>> >> Samsung R&D Institute Poland (SRPOL) | Linux Platform Group
--
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