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

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Date:   Wed, 9 Oct 2019 11:51:05 +0200
From:   Fabrice Gasnier <fabrice.gasnier@...com>
To:     Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
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 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.
 */

> 
>>  	 * Because "st,breakinput" parameter is optional do not make probe
>> -	 * failed if it doesn't exist.
>> +	 * failed if it doesn't exist. The pinctrl handle must hold the BRK
>> +	 * pin(s) when using "st,breakinput" property.
> 
> Is this a comment that has a better place in the binding doc?

You're right, this is unneeded here. I'll remove this.

Please advise,
BR,
Fabrice

> 
> Best regards
> Uwe
> 
>