Re: [PATCH v20 2/6] pwm: driver for qualcomm ipq6018 pwm block

["Uwe Kleine-König" <ukleinek@kernel.org>]

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Hello George,

On Fri, Apr 03, 2026 at 12:40:32PM +0200, George Moussalem wrote:
> On 4/2/2026 5:35 PM, Uwe Kleine-König wrote:
> > diff --git a/drivers/pwm/pwm-ipq.c b/drivers/pwm/pwm-ipq.c
> > index b944ecb456d5..4818d0170d53 100644
> > --- a/drivers/pwm/pwm-ipq.c
> > +++ b/drivers/pwm/pwm-ipq.c
> > @@ -97,9 +97,10 @@ static int ipq_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> >  	if (state->polarity != PWM_POLARITY_NORMAL)
> >  		return -EINVAL;
> >  
> > -	if (!ipq_chip->clk_rate)
> > -		return -EINVAL;
> > -
> > +	/*
> > +	 * XXX Why? A comment please. (Is this already covered by the checks
> > +	 * below?)
> > +	 */
> 
> This check can be safely removed as it is indeed covered by the check
> where the period_ns is limited to IPQ_PWM_MAX_PERIOD_NS which equals to
> NSEC_PER_SEC as per macro definition above.
> 
> >  	if (state->period < DIV64_U64_ROUND_UP(NSEC_PER_SEC,
> >  					       ipq_chip->clk_rate))
> >  		return -ERANGE;
> > @@ -107,18 +108,29 @@ static int ipq_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> >  	period_ns = min(state->period, IPQ_PWM_MAX_PERIOD_NS);
> >  	duty_ns = min(state->duty_cycle, period_ns);
> >  
> > +	/*
> > +	 * Pick the maximal value for PWM_DIV that still allows a
> > +	 * 100% relative duty cycle. This allows a fine grained
> > +	 * selection of duty cycles.
> > +	 */
> >  	pwm_div = IPQ_PWM_MAX_DIV - 1;
> > +
> > +	/*
> > +	 * XXX mul_u64_u64_div_u64 returns an u64, this might overflow the
> > +	 * unsigned int pre_div.
> > +	 */
> 
> Theoretically, yes, but in practice it won't due to above constraints.
> Take the max period of 10^9 (NSEC_PER_SEC) * max clock rate of 10^9 (1
> GHz), then the numerator becomes 10^18. Divide that by 10^9
> (NSEC_PER_SEC) * 65,535 (IPQ_PWM_MAX_DIV) and that fits well into a
> 32-bit integer.

OK, please put that in a comment.

> Do you want me to send a v21 or can you apply the diff in your tree with
> above deletion and comment?

Yes, please send a v21.

Best regards
Uwe

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