Re: [PATCH 1/5] gpio: mvebu: fix pwm get_state period calculation

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

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On Wed, Jan 13, 2021 at 08:36:12AM +0200, Baruch Siach wrote:
> Hi Uwe,
> 
> On Mon, Jan 11 2021, Uwe Kleine-König wrote:
> > $Subject ~= s/get_state/.get_state/ ?
> 
> Ack.
> 
> > On Mon, Jan 11, 2021 at 01:17:02PM +0200, Baruch Siach wrote:
> >> The period is the sum of on and off values.
> >> 
> >> Reported-by: Russell King <linux@armlinux.org.uk>
> >> Fixes: 757642f9a584e ("gpio: mvebu: Add limited PWM support")
> >> Signed-off-by: Baruch Siach <baruch@tkos.co.il>
> >> ---
> >>  drivers/gpio/gpio-mvebu.c | 19 ++++++++-----------
> >>  1 file changed, 8 insertions(+), 11 deletions(-)
> >> 
> >> diff --git a/drivers/gpio/gpio-mvebu.c b/drivers/gpio/gpio-mvebu.c
> >> index 672681a976f5..a912a8fed197 100644
> >> --- a/drivers/gpio/gpio-mvebu.c
> >> +++ b/drivers/gpio/gpio-mvebu.c
> >> @@ -676,20 +676,17 @@ static void mvebu_pwm_get_state(struct pwm_chip *chip,
> >>  	else
> >>  		state->duty_cycle = 1;
> >>  
> >> +	val = (unsigned long long) u; /* on duration */
> >>  	regmap_read(mvpwm->regs, mvebu_pwmreg_blink_off_duration(mvpwm), &u);
> >> -	val = (unsigned long long) u * NSEC_PER_SEC;
> >> +	val += (unsigned long long) u; /* period = on + off duration */
> >> +	val *= NSEC_PER_SEC;
> >>  	do_div(val, mvpwm->clk_rate);
> >> -	if (val < state->duty_cycle) {
> >> +	if (val > UINT_MAX)
> >> +		state->period = UINT_MAX;
> >> +	else if (val)
> >> +		state->period = val;
> >> +	else
> >>  		state->period = 1;
> >> -	} else {
> >> -		val -= state->duty_cycle;
> >> -		if (val > UINT_MAX)
> >> -			state->period = UINT_MAX;
> >> -		else if (val)
> >> -			state->period = val;
> >> -		else
> >> -			state->period = 1;
> >> -	}
> >
> > The patch looks good, the patch description could be a bit more verbose.
> > Something like:
> >
> > 	Calculate the period as
> >
> > 		($on + $off) / clkrate
> >
> > 	instead of
> >
> > 		$off / clkrate - $on / clkrate
> >
> > 	.
> 
> I take this to refer to the next patch (2/5). This patch changes from
> buggy
> 
>   $on / clkrate

No, the previous calculation had

-		val -= state->duty_cycle;

which accounts for "- $on / clkrate".

Best regards
Uwe

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

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