linux-kernel - Re: [PATCH 1/4] gpiolib: cdev: relocate debounce_period_us from struct gpio

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Date:   Wed, 13 Dec 2023 18:29:46 +0200
From:   Andy Shevchenko <andy@...nel.org>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Kent Gibson <warthog618@...il.com>, linux-kernel@...r.kernel.org,
        linux-gpio@...r.kernel.org, linus.walleij@...aro.org
Subject: Re: [PATCH 1/4] gpiolib: cdev: relocate debounce_period_us from
 struct gpio_desc

On Wed, Dec 13, 2023 at 05:15:38PM +0100, Bartosz Golaszewski wrote:
> On Wed, Dec 13, 2023 at 5:12 PM Andy Shevchenko <andy@...nel.org> wrote:
> > On Wed, Dec 13, 2023 at 11:59:26PM +0800, Kent Gibson wrote:
> > > On Wed, Dec 13, 2023 at 04:40:12PM +0100, Bartosz Golaszewski wrote:
> > > > On Wed, Dec 13, 2023 at 3:27 PM Kent Gibson <warthog618@...il.com> wrote:
> > > > > On Wed, Dec 13, 2023 at 03:54:53PM +0200, Andy Shevchenko wrote:
> > > > > > On Tue, Dec 12, 2023 at 01:42:50PM +0800, Kent Gibson wrote:

...

> > > > > > > +static struct supinfo supinfo;
> > > > > >
> > > > > > Why supinfo should be a struct to begin with? Seems to me as an unneeded
> > > > > > complication.
> > > >
> > > > I think we should keep it as a struct but defined the following way:
> > > >
> > > > struct {
> > > >     spinlock_t lock;
> > > >     struct rb_root tree;
> > > > } supinfo;
> > >
> > > That is what I meant be merging the struct definition with the variable
> > > definition.  Or is there some other way to completely do away with the
> > > struct that I'm missing?
> >
> > Look at the top of gpiolib.c:
> >
> > static DEFINE_MUTEX(gpio_lookup_lock);
> > static LIST_HEAD(gpio_lookup_list);
> >
> > In the similar way you can simply do
> >
> > static DEFINE_SPINLOCK(gpio_sup_lock);
> > static struct rb_root gpio_sup_tree;
> 
> The fact that this has been like this, doesn't mean it's the only
> right way. IMO putting these into the same structure makes logical
> sense.

I disagree on the struct like this on the grounds:
- it's global
- it's one time use
- it adds complications for no benefit
- it makes code uglier and longer

What we probably want to have is a singleton objects in C language or at least
inside Linux kernel project. But I'm not sure it's feasible.

> > > > > Yeah, that is a hangover from an earlier iteration where supinfo was
> > > > > contained in other object rather than being a global.
> > > > > Could merge the struct definition into the variable now.

-- 
With Best Regards,
Andy Shevchenko