Re: [PATCH v3 3/7] pwm: max7360: Add MAX7360 PWM support

[Mathieu Dubois-Briand]

On Fri Jan 17, 2025 at 10:33 AM CET, Uwe Kleine-König wrote:
> Hello Mathieu,
>
> On Mon, Jan 13, 2025 at 01:42:27PM +0100, mathieu.dubois-briand@xxxxxxxxxxx wrote:
> > From: Kamel Bouhara <kamel.bouhara@xxxxxxxxxxx>
...
> > +static int max7360_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> > +			     const struct pwm_state *state)
> > +{
> > +	struct max7360_pwm *max7360_pwm;
> > +	u64 duty_steps;
> > +	int ret;
> > +
> > +	if (state->polarity != PWM_POLARITY_NORMAL)
> > +		return -EINVAL;
> > +
> > +	if (state->period != MAX7360_PWM_PERIOD_NS) {
> > +		dev_warn(&chip->dev,
> > +			 "unsupported pwm period: %llu, should be %u\n",
> > +			 state->period, MAX7360_PWM_PERIOD_NS);
> > +		return -EINVAL;
>
> Please don't emit error messages in .apply(). Also a driver is supposed
> to round down .period, so any value >= MAX7360_PWM_PERIOD_NS should be
> accepted.
>
> Also note that you might want to implement the waveform callbacks
> instead of .apply() and .get_state() for the more modern abstraction
> (with slightly different rounding rules).
>

Sure, I just switched to the waveform callbacks, it was quite
straightforward.

> > +static int max7360_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> > +				 struct pwm_state *state)
> > +{
...
> > +	state->duty_cycle = mul_u64_u64_div_u64(val, MAX7360_PWM_PERIOD_NS,
> > +						MAX7360_PWM_MAX_RES);
>
> You have to round up here. I would expect that the checks in the core
> (with PWM_DEBUG=1) help you catching this type of error. In your case
> changing the configuration to
>
> 	.period = 2000000,
> 	.duty_cycle = 234379,
>
> should yield some hint in the kernel log.
>

Thanks for the reproduce steps: I saw the bug and fixed it. Also
MAX7360_PWM_MAX_RES had to be set to 255 and not 256...

> > +	return 0;
> > +}
>
> Best regards
> Uwe

I also fixed all other points mentioned in your mail. Thanks again for your review.

-- 
Mathieu Dubois-Briand, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com