Subject: Re: [PATCH v17 01/14] bitops: Introduce the for_each_set_clump8 macro

From: William Breathitt Gray <[email-masked]>
Date: Wed, 9 Oct 2019 13:02:40 -0400

On Thu, Oct 10, 2019 at 01:28:08AM +0900, Masahiro Yamada wrote:
> On Thu, Oct 10, 2019 at 12:27 AM William Breathitt Gray
> <[email-masked]> 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 <[email-masked]>
> > Suggested-by: Rasmus Villemoes <[email-masked]>
> > Suggested-by: Lukas Wunner <[email-masked]>
> > Cc: Arnd Bergmann <[email-masked]>
> > Cc: Andrew Morton <[email-masked]>
> > Cc: Andy Shevchenko <[email-masked]>
> > Cc: Linus Walleij <[email-masked]>
> > Signed-off-by: William Breathitt Gray <[email-masked]>
> > ---
> >  include/asm-generic/bitops/find.h | 17 +++++++++++++++
> >  include/linux/bitmap.h            | 35 +++++++++++++++++++++++++++++++
> >  include/linux/bitops.h            |  5 +++++
> >  lib/find_bit.c                    | 14 +++++++++++++
> >  4 files changed, 71 insertions(+)
> >
> > diff --git a/include/asm-generic/bitops/find.h b/include/asm-generic/bitops/find.h
> > index 8a1ee10014de..9fdf21302fdf 100644
> > --- a/include/asm-generic/bitops/find.h
> > +++ b/include/asm-generic/bitops/find.h
> > @@ -80,4 +80,21 @@ extern unsigned long find_first_zero_bit(const unsigned long *addr,
> >
> >  #endif /* CONFIG_GENERIC_FIND_FIRST_BIT */
> >
> > +/**
> > + * 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
> > + * @size: bitmap size in number of bits
> > + * @offset: bit offset at which to start searching
> > + *
> > + * 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.
> > + */
> > +extern unsigned long find_next_clump8(unsigned long *clump,
> > +                                     const unsigned long *addr,
> > +                                     unsigned long size, unsigned long offset);
> > +
> > +#define find_first_clump8(clump, bits, size) \
> > +       find_next_clump8((clump), (bits), (size), 0)
> > +
> >  #endif /*_ASM_GENERIC_BITOPS_FIND_H_ */
> > diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
> > index 90528f12bdfa..761fab5b60a7 100644
> > --- a/include/linux/bitmap.h
> > +++ b/include/linux/bitmap.h
> > @@ -66,6 +66,8 @@
> >   *  bitmap_allocate_region(bitmap, pos, order)  Allocate specified bit region
> >   *  bitmap_from_arr32(dst, buf, nbits)          Copy nbits from u32[] buf to dst
> >   *  bitmap_to_arr32(buf, src, nbits)            Copy nbits from buf to u32[] dst
> > + *  bitmap_get_value8(map, start)               Get 8bit value from map at start
> > + *  bitmap_set_value8(map, value, start)        Set 8bit value to map at start
> >   *
> >   * Note, bitmap_zero() and bitmap_fill() operate over the region of
> >   * unsigned longs, that is, bits behind bitmap till the unsigned long
> > @@ -488,6 +490,39 @@ static inline void bitmap_from_u64(unsigned long *dst, u64 mask)
> >                 dst[1] = mask >> 32;
> >  }
> >
> > +/**
> > + * bitmap_get_value8 - get an 8-bit value within a memory region
> > + * @map: address to the bitmap memory region
> > + * @start: bit offset of the 8-bit value; must be a multiple of 8
> > + *
> > + * Returns the 8-bit value located at the @start bit offset within the @src
> > + * memory region.
> > + */
> > +static inline unsigned long bitmap_get_value8(const unsigned long *map,
> > +                                             unsigned long start)
> 
> Why is the return type "unsigned long" where you know
> it return the 8-bit value ?
> 
> u8?

The primary reason is to be consistent with the datatype of the bitmap:
https://lkml.org/lkml/2019/1/12/26

This should also make it easier to extent to other sizes in the future
since we won't have to change the interface in order to support 16-bit
or 32-bit values -- they should easily fit within an unsigned long.

William Breathitt Gray

> 
> 
> 
> > +{
> > +       const size_t index = BIT_WORD(start);
> > +       const unsigned long offset = start % BITS_PER_LONG;
> > +
> > +       return (map[index] >> offset) & 0xFF;
> > +}
> > +
> > +/**
> > + * bitmap_set_value8 - set an 8-bit value within a memory region
> > + * @map: address to the bitmap memory region
> > + * @value: the 8-bit value; values wider than 8 bits may clobber bitmap
> > + * @start: bit offset of the 8-bit value; must be a multiple of 8
> > + */
> > +static inline void bitmap_set_value8(unsigned long *map, unsigned long value,
> 
> 
> Same here,   "u8 value"
> 
> 
> 
> > +                                    unsigned long start)
> > +{
> > +       const size_t index = BIT_WORD(start);
> > +       const unsigned long offset = start % BITS_PER_LONG;
> > +
> > +       map[index] &= ~(0xFF << offset);
> > +       map[index] |= value << offset;
> > +}
> > +
> >  #endif /* __ASSEMBLY__ */
> >
> >  #endif /* __LINUX_BITMAP_H */
> > diff --git a/include/linux/bitops.h b/include/linux/bitops.h
> > index cf074bce3eb3..fb94a10f7853 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), (size), (start) + 8))
> > +
> >  static inline int get_bitmask_order(unsigned int count)
> >  {
> >         int order;
> > diff --git a/lib/find_bit.c b/lib/find_bit.c
> > index 5c51eb45178a..e35a76b291e6 100644
> > --- a/lib/find_bit.c
> > +++ b/lib/find_bit.c
> > @@ -214,3 +214,17 @@ EXPORT_SYMBOL(find_next_bit_le);
> >  #endif
> >
> >  #endif /* __BIG_ENDIAN */
> > +
> > +unsigned long find_next_clump8(unsigned long *clump, const unsigned long *addr,
> 
> 
> Ditto.   "u8 *clump"
> 
> 
> 
> 
> > +                              unsigned long size, unsigned long offset)
> > +{
> > +       offset = find_next_bit(addr, size, offset);
> > +       if (offset == size)
> > +               return size;
> > +
> > +       offset = round_down(offset, 8);
> > +       *clump = bitmap_get_value8(addr, offset);
> > +
> > +       return offset;
> > +}
> > +EXPORT_SYMBOL(find_next_clump8);
> > --
> > 2.23.0
> >
> 
> 
> --
> Best Regards
> 
> Masahiro Yamada

_______________________________________________
linux-arm-kernel mailing list
[email-masked]
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel