[v16,01/14] bitops: Introduce the for_each_set_clump8 macro

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>
Suggested-by: Lukas Wunner <lukas@wunner.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
---
 include/asm-generic/bitops/find.h | 50 +++++++++++++++++++++++++++++++
 include/linux/bitops.h            |  5 ++++
 lib/find_bit.c                    | 14 +++++++++
 3 files changed, 69 insertions(+)

On Sun, Oct 06, 2019 at 11:10:58AM -0400, William Breathitt Gray 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.

Very much thank you for an update!
I have comments below.

> +/**
> + * bitmap_get_value8 - get an 8-bit value within a memory region

Since it's in find.h I would not collide with bitmap namespace.
How about

	find_and_get_value8()

> + * @addr: 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 @addr
> + * memory region.
> + */
> +static inline unsigned long bitmap_get_value8(const unsigned long *addr,
> +					      unsigned long start)
> +{
> +	const size_t index = BIT_WORD(start);
> +	const unsigned long offset = start % BITS_PER_LONG;
> +
> +	return (addr[index] >> offset) & 0xFF;
> +}
> +
> +/**
> + * bitmap_set_value8 - set an 8-bit value within a memory region

	find_and_set_value8()

?

> + * @addr: 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 *addr, unsigned long value,
> +				     unsigned long start)
> +{
> +	const size_t index = BIT_WORD(start);
> +	const unsigned long offset = start % BITS_PER_LONG;
> +
> +	addr[index] &= ~(0xFF << offset);
> +	addr[index] |= value << offset;
> +}

On Mon, Oct 07, 2019 at 11:21:56AM +0300, Andy Shevchenko wrote:
> On Sun, Oct 06, 2019 at 11:10:58AM -0400, William Breathitt Gray 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.
> 
> Very much thank you for an update!
> I have comments below.
> 
> > +/**
> > + * bitmap_get_value8 - get an 8-bit value within a memory region
> 
> Since it's in find.h I would not collide with bitmap namespace.
> How about
> 
> 	find_and_get_value8()

We modeled the interface for these on the existing bitmap functions, so
perhaps it would be better to move bitmap_get_value8 and
bitmap_set_value8 to include/linux/bitmap.h so that they are with the
rest of the bitmap functions -- afterall, they are operating on bitmaps.

> > + * @addr: 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 @addr
> > + * memory region.
> > + */
> > +static inline unsigned long bitmap_get_value8(const unsigned long *addr,
> > +					      unsigned long start)
> > +{
> > +	const size_t index = BIT_WORD(start);
> > +	const unsigned long offset = start % BITS_PER_LONG;
> > +
> > +	return (addr[index] >> offset) & 0xFF;
> > +}
> > +
> > +/**
> > + * bitmap_set_value8 - set an 8-bit value within a memory region
> 
> 	find_and_set_value8()
> 
> ?
> 
> > + * @addr: 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 *addr, unsigned long value,
> > +				     unsigned long start)
> > +{
> > +	const size_t index = BIT_WORD(start);
> > +	const unsigned long offset = start % BITS_PER_LONG;
> > +
> > +	addr[index] &= ~(0xFF << offset);
> > +	addr[index] |= value << offset;
> > +}
> 
> -- 
> With Best Regards,
> Andy Shevchenko

The find_next_clump8 function can remain exposed via
include/linux/find.h since it fits in with the rest of the functions
there.

The reason I moved the definition to lib/find_bit.c is due to the
circular dependency that arose from the round_down macro. Should I try
to move the definition back to include/linux/find.h and reimplement it
without the round_down macro; or is it best to keep this simpler
implementation here in lib/find_bit.c?

William Breathitt Gray