linux-kernel - Re: [RESEND PATCH v4 1/8] bitops: Introduce the for_each_set

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Date:   Thu, 4 Oct 2018 15:10:46 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     William Breathitt Gray <vilhelm.gray@...il.com>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        linus.walleij@...aro.org, akpm@...ux-foundation.org,
        linux-gpio@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [RESEND PATCH v4 1/8] bitops: Introduce the for_each_set_clump
 macro

On Thu, Oct 04, 2018 at 07:36:20PM +0900, William Breathitt Gray wrote:
> On Wed, Oct 03, 2018 at 02:48:04PM +0300, Andy Shevchenko wrote:
> > On Tue, Oct 02, 2018 at 11:21:42AM +0300, Andy Shevchenko wrote:
> > 
> > > I would rather go with two prototypes to get()/set() a clump in the bitmap
> > > in a way when it's aligned and BITS_PER_LONG % clump_size == 0.
> > 
> > To make things much easier, restrict clump_size to the one
> > from the following set:
> > 
> > 1, 2, 4, 8, 16, 32 even on 64-bit platforms.
> > 
> > If it would be simpler solution to add 64 here (implying 32-bit platform),
> > I would vote for that.
> > 
> > For the generic case we might need something like:
> > 
> > unsigned long bitmap_get_bits(unsigned long *src, unsigned int start, unsigned int nbits)
> > {
> > 	assert(nbits > BITS_PER_LONG);
> > 
> > 	/* Something like Rasmus proposed earlier */
> > }
> > 
> > And similar to setter.
> > 
> > 
> > -- 
> > With Best Regards,
> > Andy Shevchenko
> 
> I have no objections to have a simplier macro for these common clump
> sizes -- afterall, I suspect most drivers will likely use clump sizes
> that are powers of 2 anyway. It would be nice to have a more versatile
> macro though for those drivers that would benefit from odd clump sizes,
> but we can perhaps postpone that until the need arises (the GPIO drivers
> in this patchset all use a power of 2).

Yes, this is my point of view: don't produce additional complexity to some
which has no users (yet).

When we would really have groups out of an odd bit number, we may reconsider.

-- 
With Best Regards,
Andy Shevchenko