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

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Message-Id: <D74GSFVY17UV.GMN119MAVAK0@bootlin.com>
Date: Fri, 17 Jan 2025 16:47:45 +0100
From: "Mathieu Dubois-Briand" <mathieu.dubois-briand@...tlin.com>
To: Uwe Kleine-König <ukleinek@...nel.org>
Cc: "Lee Jones" <lee@...nel.org>, "Rob Herring" <robh@...nel.org>,
 "Krzysztof Kozlowski" <krzk+dt@...nel.org>, "Conor Dooley"
 <conor+dt@...nel.org>, "Kamel Bouhara" <kamel.bouhara@...tlin.com>, "Linus
 Walleij" <linus.walleij@...aro.org>, "Bartosz Golaszewski" <brgl@...ev.pl>,
 "Dmitry Torokhov" <dmitry.torokhov@...il.com>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <linux-gpio@...r.kernel.org>, <linux-input@...r.kernel.org>,
 <linux-pwm@...r.kernel.org>, Grégory Clement
 <gregory.clement@...tlin.com>, "Thomas Petazzoni"
 <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v3 3/7] pwm: max7360: Add MAX7360 PWM support

On Fri Jan 17, 2025 at 3:40 PM CET, Uwe Kleine-König wrote:
> On Fri, Jan 17, 2025 at 03:11:29PM +0100, Mathieu Dubois-Briand wrote:
> > 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@...tlin.com wrote:
> > > > From: Kamel Bouhara <kamel.bouhara@...tlin.com>
> > ...
> > > > +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.
>
> sounds great. Note that the detail in rounding that is different for
> waveforms is that a value that cannot be round down to a valid value
> (because it's too small) is round up. This is a bit ugly in the drivers
> but simplifies usage considerably. So you never return -EINVAL because
> the values don't fit.
>

Sorry, I'm not sure I got it right. Does this affect the three members
of pwm_waveform (period_length_ns, duty_offset_ns, duty_length_ns) ? So
on this device where the period is fixed and I cannot define an offset,
does that mean I will silently accept any value for period_length_ns and
duty_offset_ns ?

Best regards,
Mathieu

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