linux-kernel - Re: [PATCH v12 01/11] bitops: Introduce the for_each_set

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Date:   Tue, 26 Mar 2019 12:19:33 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     William Breathitt Gray <vilhelm.gray@...il.com>
Cc:     Lukas Wunner <lukas@...ner.de>, linus.walleij@...aro.org,
        bgolaszewski@...libre.com, akpm@...ux-foundation.org,
        linux-gpio@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux@...musvillemoes.dk,
        yamada.masahiro@...ionext.com,
        linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
        geert@...ux-m68k.org, preid@...ctromag.com.au,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v12 01/11] bitops: Introduce the for_each_set_clump8 macro

On Tue, Mar 26, 2019 at 07:08:18PM +0900, William Breathitt Gray wrote:
> On Tue, Mar 26, 2019 at 10:43:45AM +0100, Lukas Wunner wrote:
> > On Tue, Mar 26, 2019 at 12:14:22PM +0900, William Breathitt Gray wrote:

> > Why is it so complicated, does it allow passing in a start value
> > that's not a multiple of 8?  Do you really need that?  I imagine
> > a simplification is possible if that assumption can be made (and
> > is spelled out in the kerneldoc).
> 
> That's a good point. Originally, I had envisioned the possibility of
> calling bitmap_get_value8/bitmap_set_value8 at odd start offsets; this
> would open up the possibility of a clump landing as a split between 2
> words, thus requiring this complicated case handling code. However, I'm
> not sure how often users would need this case; none of the drivers right
> now require clumps at odd offsets.
> 
> Andy, would you have any objection to restricting the start offset
> values for bitmap_get_value8/bitmap_set_value8 to multiples of 8? That
> would prevent the split word case, and thus allow the implementation for
> those functions to be a lot simpler.

No, I have no objection.

-- 
With Best Regards,
Andy Shevchenko