linux-kernel - Re: [PATCH v2 2/5] gpiolib: cdev: relocate debounce_period_us from struct gpio

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Date: Fri, 15 Dec 2023 09:07:48 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Kent Gibson <warthog618@...il.com>
Cc: Andy Shevchenko <andy@...nel.org>, linux-kernel@...r.kernel.org, 
	linux-gpio@...r.kernel.org, linus.walleij@...aro.org
Subject: Re: [PATCH v2 2/5] gpiolib: cdev: relocate debounce_period_us from
 struct gpio_desc

On Fri, Dec 15, 2023 at 2:04 AM Kent Gibson <warthog618@...il.com> wrote:
>
> On Thu, Dec 14, 2023 at 10:06:14PM +0100, Bartosz Golaszewski wrote:
> > On Thu, Dec 14, 2023 at 5:41 PM Andy Shevchenko <andy@...nel.org> wrote:
> > >
> > > On Fri, Dec 15, 2023 at 12:14:41AM +0800, Kent Gibson wrote:
> > > > On Thu, Dec 14, 2023 at 05:09:01PM +0200, Andy Shevchenko wrote:
> > > > > On Thu, Dec 14, 2023 at 05:03:03PM +0200, Andy Shevchenko wrote:
> > > > > > On Thu, Dec 14, 2023 at 05:58:11PM +0800, Kent Gibson wrote:
> > >
> > > ...
> > >
> > > > > > > +static void supinfo_init(void)
> > > > > > > +{
> > > > > > > +       supinfo.tree = RB_ROOT;
> > > > > > > +       spin_lock_init(&supinfo.lock);
> > > > > > > +}
> > > > > >
> > > > > > Can it be done statically?
> > > > > >
> > > > > > supinfo = {
> > > > > >   .tree = RB_ROOT,
> > > > > >   .lock = __SPIN_LOCK_UNLOCKED(supinfo.lock),
> >
> > Double underscore typically means it's private and shouldn't be used.
> >
>
> You mean like __assign_bit(), __set_bit(), __clear_bit() and __free() -
> all used in gpiolib.c?
>

Touché. But this is just lack of strict naming conventions. :( Another
common use of leading underscores are "unlocked" (or in this case:
non-atomic) variants of functions.

> > > > >
> > > > > I even checked the current tree, we have 32 users of this pattern in drivers/.
> > > >

As opposed to ~1200 uses of DEFINE_SPINLOCK if you really want to go there. :)

> > > > Ah, that is what you meant.  Yeah sure can - the supinfo_init() is
> > > > another hangover from when I was trying to create the supinfo per chip,
> > > > but now it is a global a static initialiser makes sense.
> > >
> > > Yep, the DEFINE_MUTEX() / DEFINE_SPINLOCK() / etc looks better naturally
> > > than above.
> >
> > Yeah, so maybe we should use non-struct, global variables after all.
> >
>
> Despite the 32 cases cited that already use that pattern?
> 9 of which use __SPIN_LOCK_UNLOCKED().
> Sounds like a pretty convincing argument to use the struct ;-).
>
> But lets keep it as kosher as possible and split out the struct :-(.
>

I'll leave it for you to decide, I don't have a strong opinion and the
entire file is your code so you should pick.

Bart

> Cheers,
> Kent.
>