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

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Message-ID: <20191008144531.pjt525xuz7n5a3hq@pengutronix.de>
Date:   Tue, 8 Oct 2019 16:45:31 +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 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.

>  	 * 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?

Best regards
Uwe


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