linux-kernel - Re: [PATCH v5 6/7] pwm: lpss: Add devm_pwm_lpss

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Message-ID: <20221122181444.m74fa47ejp7nvgxj@pengutronix.de>
Date:   Tue, 22 Nov 2022 19:14:44 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-pwm@...r.kernel.org, Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v5 6/7] pwm: lpss: Add devm_pwm_lpss_probe() stub

Hello Andy,

On Tue, Nov 22, 2022 at 07:35:38PM +0200, Andy Shevchenko wrote:
> On Tue, Nov 22, 2022 at 05:47:03PM +0100, Uwe Kleine-König wrote:
> > On Thu, Nov 17, 2022 at 01:08:05PM +0200, Andy Shevchenko wrote:
> > > In case the PWM LPSS module is not provided, allow users to be
> > > compiled with the help of the devm_pwm_lpss_probe() stub.
> 
> ...
> 
> > > +static inline
> > > +struct pwm_lpss_chip *devm_pwm_lpss_probe(struct device *dev, void __iomem *base,
> > > +					  const struct pwm_lpss_boardinfo *info)
> > > +{
> > > +	return ERR_PTR(-ENODEV);
> > > +}
> > > +#endif	/* CONFIG_PWM_LPSS */
> > 
> > Hmm, this is actually never used, because if
> > !IS_REACHABLE(CONFIG_PWM_LPSS), the only caller (that is added in patch
> > 7) has:
> > 
> > 	if (!IS_REACHABLE(CONFIG_PWM_LPSS))
> > 		return 0;
> > 
> > before devm_pwm_lpss_probe() is called.
> > 
> > Not sure if it's safe to just drop this patch.
> 
> How is it supposed to be compiled and linked then?

The compiler optimizes everything away after that return 0 and so
doesn't need that symbol at all.

I just tested compiling your series without patch #6, x86_64 allmodconfig + PWM=n.

nm doesn't report the need for devm_pwm_lpss_probe in
drivers/pinctrl/intel/pinctrl-intel.o.

The build isn't done yet, but I don't expect surprises.

Best regards
Uwe

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

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