guard coding style (was: Re: [PATCH v1 05/10] gpio: pca953x: Simplify code with cleanup helpers)

[Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>]

Hi Bartosz,

On Wed, Sep 13, 2023 at 5:27 PM Bartosz Golaszewski <brgl@xxxxxxxx> wrote:
> On Wed, Sep 13, 2023 at 4:35 PM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
> > On Fri, 1 Sep 2023, Andy Shevchenko wrote:
> > > Use macros defined in linux/cleanup.h to automate resource lifetime
> > > control in gpio-pca953x.
> > >
> > > Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> >
> > Thanks for your patch, which is now commit 8e471b784a720f6f
> > ("gpio: pca953x: Simplify code with cleanup helpers") in
> > gpio/gpio/for-next.
> >
> > > --- a/drivers/gpio/gpio-pca953x.c
> > > +++ b/drivers/gpio/gpio-pca953x.c
> > > @@ -557,9 +554,8 @@ static int pca953x_gpio_get_value(struct gpio_chip *gc, unsigned off)
> > >       u32 reg_val;
> > >       int ret;
> > >
> > > -     mutex_lock(&chip->i2c_lock);
> > > -     ret = regmap_read(chip->regmap, inreg, &reg_val);
> > > -     mutex_unlock(&chip->i2c_lock);
> > > +     scoped_guard(mutex, &chip->i2c_lock)
> > > +             ret = regmap_read(chip->regmap, inreg, &reg_val);
> >
> > I can't say I'm thrilled about the lack of curly braces.  I was also
> > surprised to discover that checkpatch nor gcc W=1 complain about the
> > indentation change.
> > I know we don't use curly braces in single-statement for_each_*() loops,
> > but at least these have the familiar "for"-prefix.  And having the scope
> > is very important here, so using braces, this would stand out more.
> >
> > Hence can we please get curly braces, like
> >
> >      scoped_guard(mutex, &chip->i2c_lock) {
> >             ret = regmap_read(chip->regmap, inreg, &reg_val);
> >      }
> >
> > ?
> >
> > Thanks! ;-)
>
> I strongly disagree. The scope here is very clear - just like it is in
> a for loop, in a while loop or in an if block:
>
> if (foo)
>     bar()
>
> if (foo) {
>     bar();
>     baz();
> }
>
> Only compound statements need curly braces in the kernel and it has
> been like this forever. I don't really see a need to make it an
> exception.
>
> That being said - I don't think the coding style for guard has ever
> been addressed yet, so maybe bring it up with Peter Zijlstra?

That's a good idea!

I see Peter always used curly braces (but he didn't have any
single-statement blocks, except for one with an "if", and we do tend
to use curly braces in "for"-statements containing a single "if", too),
but he does put a space after the "scoped_guard", as is also
shown in the template in include/linux/cleanup.h:

    scoped_guard (name, args...) { }:

Then, "guard" does not get a space (but it is funny syntax
anyway, with the double set of parentheses ;-).  The template in
include/linux/cleanup.h doesn't match actual usage as it lacks the
second set of parentheses:

    guard(name):

Peter: care to comment?
Or do you have a different bikeshed to paint today? ;-)

Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds