linux-kernel - Re: [PATCH v2] gpio: mockup: Allow probing from device tree

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Date:   Wed, 28 Oct 2020 09:57:46 +0100
From:   Vincent Whitchurch <vincent.whitchurch@...s.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
CC:     Bamvor Jian Zhang <bamv2005@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        kernel <kernel@...s.com>,
        devicetree <devicetree@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] gpio: mockup: Allow probing from device tree

On Tue, Oct 27, 2020 at 07:12:13PM +0100, Bartosz Golaszewski wrote:
> On Tue, Oct 27, 2020 at 2:54 PM Vincent Whitchurch
> <vincent.whitchurch@...s.com> wrote:
> > diff --git a/drivers/gpio/gpio-mockup.c b/drivers/gpio/gpio-mockup.c
> > index 67ed4f238d43..c93892a6936a 100644
> > --- a/drivers/gpio/gpio-mockup.c
> > +++ b/drivers/gpio/gpio-mockup.c
> > @@ -13,6 +13,7 @@
> >  #include <linux/gpio/driver.h>
> >  #include <linux/interrupt.h>
> >  #include <linux/irq.h>
> > +#include <linux/of.h>
> 
> Please keep the includes ordered alphabetically.

Thanks, fixed in v3.

> >  #include <linux/irq_sim.h>
> >  #include <linux/irqdomain.h>
> >  #include <linux/module.h>
> > @@ -460,9 +461,18 @@ static int gpio_mockup_probe(struct platform_device *pdev)
> >         return 0;
> >  }
> >
> > +#ifdef CONFIG_OF
> > +static const struct of_device_id gpio_mockup_of_match[] = {
> > +       { .compatible = "gpio-mockup", },
> > +       {},
> > +};
> > +MODULE_DEVICE_TABLE(of, gpio_mockup_of_match);
> > +#endif
> 
> You don't need this ifdef - of_match_ptr() will evaluate to NULL if
> CONFIG_OF is disabled and the compiler will optimize this struct out.

The compiler can't optimise out the struct in the case of a module build
since there is a reference from the MODULE_DEVICE_TABLE:

 $ grep CONFIG_OF .config
 # CONFIG_OF is not set
 $ nm drivers/gpio/gpio-mockup.ko  | grep of_
 00000000 r gpio_mockup_of_match
 00000000 R __mod_of__gpio_mockup_of_match_device_table

But these few wasted bytes don't matter so I removed the CONFIG_OF
anyway as you suggested.