linux-kernel - Re: [RESEND PATCH v4 3/8] gpio: 104-dio-48e: Utilize for_each_set

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Date:   Wed, 17 Oct 2018 10:54:02 +0900
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     linus.walleij@...aro.org, akpm@...ux-foundation.org,
        linux-gpio@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, andriy.shevchenko@...ux.intel.com
Subject: Re: [RESEND PATCH v4 3/8] gpio: 104-dio-48e: Utilize
 for_each_set_clump macro

On Mon, Oct 15, 2018 at 01:59:33PM +0200, Rasmus Villemoes wrote:
> On 2018-10-14 06:19, William Breathitt Gray wrote:
> 
> > a bit value of 0 in the
> > bits array does not necessarily mean the input was not requested, but
> > may instead mean that the value at the input is 0;
> 
> sure enough, but...
> 
> > therefore, the caller
> > must keep track of the requested inputs rather than try to deduce them
> > from the values in the bits array.
> 
> ...I don't agree that this logically follows. A caller might reasonably
> expect not to find any bits set in positions other than those in mask. A
> simple example would be caller that just tried to ask "are any of
> _these_ inputs set"; it would be reasonable to implement that using
> bitmap_empty() on the returned bitset, without first having to mask by
> the mask he passed in.
> 
> Rasmus

I see your point. It would be good to keep the behavior consistent with
what would be expected by the user -- and adding an additional AND
operation at the end to mask away the unrequested bits should not really
affect the performance to a discernible degree -- so I'll submit a
patchset implementing the mask for these drivers some time this weekend.

William Breathitt Gray