linux-kernel - Re: [PATCH] gpio: sim: don't fiddle with GPIOLIB private members

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Message-ID: <CAMRc=MfZv70FXHyNw4yK90NL5-jjAJa6qbKc6SV2ZwbaJkKQqg@mail.gmail.com>
Date:   Mon, 4 Sep 2023 11:22:32 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Kent Gibson <warthog618@...il.com>, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH] gpio: sim: don't fiddle with GPIOLIB private members

On Mon, Sep 4, 2023 at 10:59 AM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Sat, Sep 02, 2023 at 04:40:05PM +0200, Bartosz Golaszewski wrote:
> > On Fri, Sep 1, 2023 at 11:10 PM Andy Shevchenko
> > <andriy.shevchenko@...ux.intel.com> wrote:
> > > On Fri, Sep 01, 2023 at 08:32:40PM +0200, Bartosz Golaszewski wrote:
>
> ...
>
> > > > -static void gpio_sim_free(struct gpio_chip *gc, unsigned int offset)
> > >
> > > Why is this?
> >
> > Dunno, some git shenanigans?
>
> Time to use --patience then?
>

Ha! I wasn't even aware you can use this with format-patch. Looks much
better indeed.

> ...
>
> > > > -     /* Used by sysfs and configfs callbacks. */
> > > > -     dev_set_drvdata(&gc->gpiodev->dev, chip);
> > > > +     /* Used by sysfs callbacks. */
> > > > +     dev_set_drvdata(swnode->dev, chip);
> > >
> > > dev pointer of firmware node is solely for dev links. Is it the case here?
> > > Seems to me you luckily abuse it.
> >
> > I don't think so. If anything we have a helper in the form of
> > get_dev_from_fwnode() but it takes reference to the device while we
> > don't need it - we know it'll be there because we created it.
> >
> > This information (struct device of the GPIO device) can also be
> > retrieved by iterating over the device children of the top platform
> > device and comparing their fwnodes against the one we got passed down
> > from probe() but it's just so many extra steps.
> >
> > Or we can have a getter in gpio/driver.h for that but I don't want to
> > expose another interface is we can simply use the fwnode.
>
> dev pointer in the fwnode strictly speaking is optional. No-one, except
> its solely user, should rely on it (its presence and lifetime).
>

Where is this documented? Because just by a quick glance into
drivers/base/core.c I can tell that if a device has an fwnode then
fwnode->dev gets assigned when the device is created and cleared when
it's removed (note: note even attached to driver, just
created/removed). Seems like pretty reliable behavior to me.

Bart

> --
> With Best Regards,
> Andy Shevchenko
>
>