[PATCH v3 5/5] gpio: mvebu: document zero pwm duty cycle limitation

[Uwe Kleine-König]

Hello Baruch,

On Thu, Jan 14, 2021 at 08:57:37PM +0200, Baruch Siach wrote:
> Add a comment on why the code never sets on/off registers to zero.
> 
> Reported-by: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
> Analyzed-by: Russell King <linux at armlinux.org.uk>
> Signed-off-by: Baruch Siach <baruch at tkos.co.il>
> ---
>  drivers/gpio/gpio-mvebu.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpio/gpio-mvebu.c b/drivers/gpio/gpio-mvebu.c
> index 6b017854ce61..09780944bef9 100644
> --- a/drivers/gpio/gpio-mvebu.c
> +++ b/drivers/gpio/gpio-mvebu.c
> @@ -706,6 +706,10 @@ static int mvebu_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>  	do_div(val, NSEC_PER_SEC);
>  	if (val > UINT_MAX)
>  		return -EINVAL;
> +	/*
> +	 * Zero on/off values don't work as expected. Experimentation shows
> +	 * that zero value is treated as 2^32. This behavior is not documented.
> +	 */

This is too easy. The right thing to do is to adapt .apply and
.get_state to use this new information.

Best regards
Uwe

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