linux-kernel - Re: [PATCH RCC 1/6] pwm: Add different PWM output types support

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Message-ID: <20200728075257.efhsju2odehpbv6f@pengutronix.de>
Date:   Tue, 28 Jul 2020 09:52:57 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Martin Botka <martin.botka1@...il.com>
Cc:     Fenglin Wu <fenglinw@...eaurora.org>,
        Konrad Dybcio <konradybcio@...il.com>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>, Dan Murphy <dmurphy@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-pwm@...r.kernel.org
Subject: Re: [PATCH RCC 1/6] pwm: Add different PWM output types support

Hello Martin,

On Mon, Jul 27, 2020 at 10:56:31PM +0200, Martin Botka wrote:
> Mo 27. 7. 2020 at 22:10 Uwe Kleine-König <u.kleine-koenig@...gutronix.de> wrote:
> > On Fri, Jul 24, 2020 at 11:36:51PM +0200, Martin Botka wrote:
> > > +/*
> > > + * pwm_output_type_support()
> > > + * @pwm: PWM device
> > > + *
> > > + * Returns:  output types supported by the PWM device
> > > + */
> > > +static inline int pwm_get_output_type_supported(struct pwm_device *pwm)
> > > +{
> > > +     if (pwm->chip->ops->get_output_type_supported != NULL)
> > > +             return pwm->chip->ops->get_output_type_supported(pwm->chip, pwm);
> > > +     else
> > > +             return PWM_OUTPUT_FIXED;
> > > +}
> >
> > I don't like this "advertising" for specific functions. I'd prefer to
> > handle this in .apply(), fix all drivers to return -ESOMETHING when the
> > request cannot be fulfilled.
> 
> I will have to disagree on this one. As the functions are called in
> multiple places it would just make mess in the driver.

Note this is something where (I think) I don't agree with Thierry
either. This popped up just yesterday, see

	https://www.spinics.net/lists/linux-pwm/msg13290.html

For sure I want at most one such function per driver, so if we really
want to go this path and introduce a capability indicator, this should
be named differently and have a different prototype.

> As the driver is even now not exactly the definition of clean driver i
> would not like to make it even more messy.

> > Having said that I wonder if this output pattern is a common enough
> > property to add support for it in the PWM framework.
> >
> 
> I have gotten an email from Guru Das Srinagesh regarding this exact
> issue you are pointing to. Yes the output pattern will be dropped in
> V2.

That's good.

Best regards
Uwe

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

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