linux-kernel - Re: [PATCH] pwm: stm32: add comment to better describe breakinput feature

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Date:   Thu, 10 Oct 2019 09:07:41 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Fabrice Gasnier <fabrice.gasnier@...com>
Cc:     thierry.reding@...il.com, alexandre.torgue@...com,
        benjamin.gaignard@...com, linux-pwm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH] pwm: stm32: add comment to better describe breakinput
 feature

On Wed, Oct 09, 2019 at 11:51:05AM +0200, Fabrice Gasnier wrote:
> On 10/8/19 4:45 PM, Uwe Kleine-König wrote:
> > On Tue, Oct 08, 2019 at 01:41:27PM +0200, Fabrice Gasnier wrote:
> >> Add a comment to better describe the purpose of breakinput feature that
> >> can be found on some STM32 timer instances. Briefly comment on the
> >> characteristics of this input for PWM, and pinmuxing as suggested in [1].
> >>
> >> [1] https://lkml.org/lkml/2019/10/1/207
> >>
> >> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@...com>
> >> ---
> >>  drivers/pwm/pwm-stm32.c | 8 +++++++-
> >>  1 file changed, 7 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/pwm/pwm-stm32.c b/drivers/pwm/pwm-stm32.c
> >> index 359b085..6406ebb 100644
> >> --- a/drivers/pwm/pwm-stm32.c
> >> +++ b/drivers/pwm/pwm-stm32.c
> >> @@ -522,8 +522,14 @@ static int stm32_pwm_apply_breakinputs(struct stm32_pwm *priv,
> >>  					     sizeof(struct stm32_breakinput));
> >>  
> >>  	/*
> >> +	 * Some timer instances can have BRK input pins (e.g. basically a fault
> >> +	 * pin from the output power stage). The break feature allows a safe
> >> +	 * shut-down of the PWM outputs to a predefined state. Further details
> >> +	 * are available in application note AN4277, "Using STM32 device PWM
> >> +	 * shut-down features..."
> > 
> > Without having read the application note I don't understand the purpose.
> > Not sure if this should be a show stopper though.
> 
> Hi Uwe,
> 
> I can rephrase this. Do you think the bellow comment would be more
> relevant and easy to understand ?
> 
> /*
>  * The break feature allows a safe shut-down of the PWM outputs.
>  * It's based on the BRK event signal defined in the dt-bindings
>  * by <index level filter> values.
>  * Because "st,breakinput" parameter is optional do not make probe
>  * failed if it doesn't exist.
>  */

I still fail to understand. This is an input that determines the actual
value of the output pin? What makes a shutdown of outputs safe? What is
a shutdown anyhow?

Apart from that: s/do not make probe failed/don't fail to probe/.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |