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Date: Tue, 26 Mar 2019 19:28:43 +0900 From: William Breathitt Gray <vilhelm.gray@...il.com> To: Andy Shevchenko <andy.shevchenko@...il.com>, Lukas Wunner <lukas@...ner.de> Cc: 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 12:19:33PM +0200, Andy Shevchenko wrote: > 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 In this case, bitmap_get_value8 could be simplified to something like this: index = BIT_WORD(start); offset = start % BITS_PER_LONG; return (bitmap[index] >> offset) & 0xFF; Or if you prefer a single line: (bitmap[BIT_WORD(start)] >> (start % BITS_PER_LONG)) & 0xFF; Would it be better to define bitmap_get_value8 as a macro then? William Breathitt Gray
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