linux-kernel - Re: [PATCH v17 01/14] bitops: Introduce the for_each_set

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Date:   Wed, 9 Oct 2019 20:54:04 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        William Breathitt Gray <vilhelm.gray@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux PM mailing list <linux-pm@...r.kernel.org>,
        Phil Reid <preid@...ctromag.com.au>,
        Lukas Wunner <lukas@...ner.de>, sean.nyekjaer@...vas.dk,
        morten.tiljeset@...vas.dk, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v17 01/14] bitops: Introduce the for_each_set_clump8 macro

Hi Andy,

On Wed, Oct 9, 2019 at 7:09 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
> On Thu, Oct 10, 2019 at 01:28:08AM +0900, Masahiro Yamada wrote:
> > On Thu, Oct 10, 2019 at 12:27 AM William Breathitt Gray
> > <vilhelm.gray@...il.com> wrote:
> > >
> > > This macro iterates for each 8-bit group of bits (clump) with set bits,
> > > within a bitmap memory region. For each iteration, "start" is set to the
> > > bit offset of the found clump, while the respective clump value is
> > > stored to the location pointed by "clump". Additionally, the
> > > bitmap_get_value8 and bitmap_set_value8 functions are introduced to
> > > respectively get and set an 8-bit value in a bitmap memory region.
>
> > Why is the return type "unsigned long" where you know
> > it return the 8-bit value ?
>
> Because bitmap API operates on unsigned long type. This is not only
> consistency, but for sake of flexibility in case we would like to introduce
> more calls like clump16 or so.

TBH, that doesn't convince me: those functions explicitly take/return an
8-bit value, and have "8" in their name.  The 8-bit value is never
really related to, retrieved from, or stored in a full "unsigned long"
element of a bitmap, only to/from/in a part (byte) of it.

Following your rationale, all of iowrite{8,16,32,64}*() should take an
"unsigned long" value, too.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

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