linux-kernel - Re: [PATCH v9 1/9] bitops: Introduce the for_each_set

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Message-ID: <CAHp75VdaHYoXCqmnt=F_mnaTnCedLqs6CL1aC-oPFRdNJCAUCA@mail.gmail.com>
Date:   Fri, 8 Mar 2019 11:19:16 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     William Breathitt Gray <vilhelm.gray@...il.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v9 1/9] bitops: Introduce the for_each_set_clump8 macro

On Fri, Mar 8, 2019 at 10:56 AM William Breathitt Gray
<vilhelm.gray@...il.com> wrote:
> On Fri, Mar 08, 2019 at 09:31:00AM +0100, Linus Walleij wrote:
> > On Sun, Mar 3, 2019 at 8:47 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.

> > Andrew: would you be OK with this being merged in v5.1?
> >
> > If we need to move the code to drivers/gpio that's OK (though
> > I think it's generally useful) but I need to know to proceed with
> > the William's nice optimization of these drivers.
> >
> > Yours,
> > Linus Walleij
>
> I was waiting on Andy to suggest some examples out of the GPIO realm,
> but he may be under a heavy workload right

Yeah, sorry for that. I will use your helpers in the future for sure
in the suitable parts of the code inside and outside of GPIO, just not
in a highest priority to me.

> so I decided to do a quick
> Consider this, if I am able to find a use for this macro outside of the
> GPIO subsystem within a matter minutes, then there must be some benefit
> in allowing the rest of the kernel to use the for_each_set_clump8 macro.
> So let's put it in bitops.h rather than restrict it to just the GPIO
> subsystem.

As I mentioned earlier I'm pretty sure I found as well opportunity to
use this new API
outside of GPIO realm. I just want to be sure (means of testing on real HW).

-- 
With Best Regards,
Andy Shevchenko