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From:   Masahiro Yamada <yamada.masahiro@socionext.com>
Date:   Tue, 12 Mar 2019 12:52:51 +0900
Message-ID: <CAK7LNATsuQRj9-zT-+joRxjX1ePVG4ofeT=KS84Cjid2C5_v4Q@mail.gmail.com>
Subject: Re: [PATCH v9 1/9] bitops: Introduce the for_each_set_clump8 macro
To:     William Breathitt Gray <vilhelm.gray@gmail.com>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        bgolaszewski@baylibre.com,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        Andy Shevchenko <andy.shevchenko@gmail.com>,
        Arnd Bergmann <arnd@arndb.de>
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Sender: linux-kernel-owner@vger.kernel.org
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On Sun, Mar 3, 2019 at 4:48 PM William Breathitt Gray
<vilhelm.gray@gmail.com> wrote:
>
> This macro iterates for each 8-bit group of bits (clump) with set bits,
> within a bitmap memory region. For each iteration, "start" is set to the
> bit offset of the found clump, while the respective clump value is
> stored to the location pointed by "clump". Additionally, the
> bitmap_get_value8 and bitmap_set_value8 functions are introduced to
> respectively get and set an 8-bit value in a bitmap memory region.
>
> Suggested-by: Andy Shevchenko <andy.shevchenko@gmail.com>
> Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
> Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
> Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
> ---
>  include/asm-generic/bitops/find.h | 14 ++++++
>  include/linux/bitops.h            |  5 ++
>  lib/find_bit.c                    | 81 +++++++++++++++++++++++++++++++
>  3 files changed, 100 insertions(+)
>
> diff --git a/include/asm-generic/bitops/find.h b/include/asm-generic/bitops/find.h
> index 8a1ee10014de..9a76adff59c6 100644
> --- a/include/asm-generic/bitops/find.h
> +++ b/include/asm-generic/bitops/find.h
> @@ -80,4 +80,18 @@ extern unsigned long find_first_zero_bit(const unsigned long *addr,
>
>  #endif /* CONFIG_GENERIC_FIND_FIRST_BIT */
>
> +unsigned long bitmap_get_value8(const unsigned long *const bitmap,
> +                               const unsigned int size,
> +                               const unsigned int start);
> +
> +void bitmap_set_value8(unsigned long *const bitmap, const unsigned int size,
> +                      const unsigned long value, const unsigned int start);
> +
> +unsigned int find_next_clump8(unsigned long *const clump,
> +                             const unsigned long *const addr,
> +                             unsigned int offset, const unsigned int size);
> +
> +#define find_first_clump8(clump, bits, size) \
> +       find_next_clump8((clump), (bits), 0, (size))
> +
>  #endif /*_ASM_GENERIC_BITOPS_FIND_H_ */
> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
> index 705f7c442691..61c10f20079e 100644
> --- a/include/linux/bitops.h
> +++ b/include/linux/bitops.h
> @@ -40,6 +40,11 @@ extern unsigned long __sw_hweight64(__u64 w);
>              (bit) < (size);                                    \
>              (bit) = find_next_zero_bit((addr), (size), (bit) + 1))
>
> +#define for_each_set_clump8(start, clump, bits, size) \
> +       for ((start) = find_first_clump8(&(clump), (bits), (size)); \
> +            (start) < (size); \
> +            (start) = find_next_clump8(&(clump), (bits), (start) + 8, (size)))
> +
>  static inline int get_bitmask_order(unsigned int count)
>  {
>         int order;
> diff --git a/lib/find_bit.c b/lib/find_bit.c
> index ee3df93ba69a..c2af1f013ea2 100644
> --- a/lib/find_bit.c
> +++ b/lib/find_bit.c
> @@ -218,3 +218,84 @@ EXPORT_SYMBOL(find_next_bit_le);
>  #endif
>
>  #endif /* __BIG_ENDIAN */
> +
> +/**
> + * bitmap_get_value8 - get an 8-bit value within a memory region
> + * @bitmap: address to the bitmap memory region
> + * @size: bitmap size in number of bits
> + * @start: bit offset of the 8-bit value
> + *
> + * Returns the 8-bit value located at the @start bit offset within the @bitmap
> + * memory region.
> + */
> +unsigned long bitmap_get_value8(const unsigned long *const bitmap,
> +                               const unsigned int size,
> +                               const unsigned int start)


A bunch of 'const' qualifiers are eyesore.

The first 'const' of bitmap is the only useful one.


unsigned long bitmap_get_value8(const unsigned long *bitmap, unsigned int size,
                                unsigned int start)

is enough.


> +{
> +       const size_t index = BIT_WORD(start);
> +       const unsigned int offset = start % BITS_PER_LONG;
> +       const unsigned int low_width = (offset + 8 > BITS_PER_LONG) ?
> +                                      BITS_PER_LONG - offset : 8;
> +       const unsigned long low = bitmap[index] >> offset;
> +       const unsigned long high = (low_width < 8 && start + 8 <= size) ?
> +                                  bitmap[index + 1] << low_width : 0;


Meh.


> +
> +       return (low | high) & 0xFF;
> +}
> +EXPORT_SYMBOL(bitmap_get_value8);
> +
> +/**
> + * bitmap_set_value8 - set an 8-bit value within a memory region
> + * @bitmap: address to the bitmap memory region
> + * @size: bitmap size in number of bits
> + * @value: the 8-bit value; values wider than 8 bits may clobber bitmap
> + * @start: bit offset of the 8-bit value
> + */
> +void bitmap_set_value8(unsigned long *const bitmap, const unsigned int size,
> +                      const unsigned long value, const unsigned int start)
> +{
> +       const size_t index = BIT_WORD(start);
> +       const unsigned int offset = start % BITS_PER_LONG;
> +       const unsigned int low_width = (offset + 8 > BITS_PER_LONG) ?
> +                                      BITS_PER_LONG - offset : 8;
> +       const unsigned long low_mask = GENMASK(offset + low_width - 1, offset);
> +       const unsigned int high_width = 8 - low_width;
> +       const unsigned long high_mask = GENMASK(high_width - 1, 0);
> +
> +       /* set lower portion */
> +       bitmap[index] &= ~low_mask;
> +       bitmap[index] |= value << offset;
> +
> +       /* set higher portion if space available in bitmap */
> +       if (high_width && start + 8 <= size) {
> +               bitmap[index + 1] &= ~high_mask;
> +               bitmap[index + 1] |= value >> low_width;
> +       }
> +}
> +EXPORT_SYMBOL(bitmap_set_value8);
> +
> +/**
> + * find_next_clump8 - find next 8-bit clump with set bits in a memory region
> + * @clump: location to store copy of found clump
> + * @addr: address to base the search on
> + * @offset: bit offset at which to start searching
> + * @size: bitmap size in number of bits
> + *
> + * Returns the bit offset for the next set clump; the found clump value is
> + * copied to the location pointed by @clump. If no bits are set, returns @size.
> + */
> +unsigned int find_next_clump8(unsigned long *const clump,
> +                             const unsigned long *const addr,
> +                             unsigned int offset, const unsigned int size)
> +{
> +       for (; offset < size; offset += 8) {
> +               *clump = bitmap_get_value8(addr, size, offset);
> +               if (!*clump)
> +                       continue;
> +
> +               return offset;
> +       }
> +
> +       return size;
> +}
> +EXPORT_SYMBOL(find_next_clump8);
> --
> 2.21.0
>


-- 
Best Regards
Masahiro Yamada