linux-kernel - Re: [PATCH v12 4/4] gpio: xilinx: Utilize generic bitmap_get_value and _set

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Date:   Mon, 9 Nov 2020 12:31:23 -0500
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Syed Nayyar Waris <syednwaris@...il.com>,
        Arnd Bergmann <arnd@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michal Simek <michal.simek@...inx.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v12 4/4] gpio: xilinx: Utilize generic bitmap_get_value
 and _set_value

On Mon, Nov 09, 2020 at 07:22:20PM +0200, Andy Shevchenko wrote:
> On Mon, Nov 09, 2020 at 12:11:40PM -0500, William Breathitt Gray wrote:
> > On Mon, Nov 09, 2020 at 10:15:29PM +0530, Syed Nayyar Waris wrote:
> > > On Mon, Nov 09, 2020 at 03:41:53PM +0100, Arnd Bergmann wrote:
> 
> ...
> 
> > >  static inline void bitmap_set_value(unsigned long *map,
> > > -                                    unsigned long value,
> > > +                                    unsigned long value, const size_t length,
> > >                                      unsigned long start, unsigned long nbits)
> > >  {
> > >          const size_t index = BIT_WORD(start);
> > > @@ -15,6 +15,10 @@ static inline void bitmap_set_value(unsigned long *map,
> > >          } else {
> > >                  map[index + 0] &= ~BITMAP_FIRST_WORD_MASK(start);
> > >                  map[index + 0] |= value << offset;
> > > +
> > > +               if (index + 1 >= length)
> > > +                       __builtin_unreachable();
> > > +
> > >                  map[index + 1] &= ~BITMAP_LAST_WORD_MASK(start + nbits);
> > >                  map[index + 1] |= value >> space;
> > >          }
> > 
> > Hi Syed,
> > 
> > Let's rename 'length' to 'nbits' as Arnd suggested, and rename 'nbits'
> > to value_width.
> 
> length here is in longs. I guess this is the point of entire patch.

Ah yes, this should become 'const unsigned long nbits' and represent the
length of the bitmap in bits and not longs.

> But to me sounds like it would be better to have simply bitmap_set_value64() /
> bitmap_set_value32() with proper optimization done and forget about variadic
> ones for now.

The gpio-xilinx driver can have arbitrary sizes for width[0] and
width[1], so unfortunately that means we don't know the start position
nor the width of the value beforehand.

William Breathitt Gray

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