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SubjectRe: [PATCH v8 0/8] Introduce the for_each_set_clump8 macro
On Mon, 14 Jan 2019 15:19:17 +0900 William Breathitt Gray <vilhelm.gray@gmail.com> wrote:

> While adding GPIO get_multiple/set_multiple callback support for various
> drivers, I noticed a pattern of looping manifesting that would be useful
> standardized as a macro.
>
> This patchset introduces the for_each_set_clump8 macro and utilizes it
> in several GPIO drivers. The for_each_set_clump macro8 facilitates a
> for-loop syntax that iterates over a memory region entire groups of set
> bits at a time.
>
> For example, suppose you would like to iterate over a 32-bit integer 8
> bits at a time, skipping over 8-bit groups with no set bit, where
> XXXXXXXX represents the current 8-bit group:
>
> Example: 10111110 00000000 11111111 00110011
> First loop: 10111110 00000000 11111111 XXXXXXXX
> Second loop: 10111110 00000000 XXXXXXXX 00110011
> Third loop: XXXXXXXX 00000000 11111111 00110011
>
> Each iteration of the loop returns the next 8-bit group that has at
> least one set bit.
>
> The for_each_set_clump8 macro has four parameters:
>
> * start: set to the bit offset of the current clump
> * clump: set to the current clump value
> * bits: bitmap to search within
> * size: bitmap size in number of bits
>
> In this version of the patchset, the for_each_set_clump macro has been
> reimplemented and simplified based on the suggestions provided by Rasmus
> Villemoes and Andy Shevchenko in the version 4 submission.
>
> In particular, the function of the for_each_set_clump macro has been
> restricted to handle only 8-bit clumps; the drivers that use the
> for_each_set_clump macro only handle 8-bit ports so a generic
> for_each_set_clump implementation is not necessary. Thus, a solution for
> large clumps (i.e. those larger than the width of a bitmap word) can be
> postponed until a driver appears that actually requires such a generic
> for_each_set_clump implementation.
>
> For what it's worth, a semi-generic for_each_set_clump (i.e. for clumps
> smaller than the width of a bitmap word) can be implemented by simply
> replacing the hardcoded '8' and '0xFF' instances with respective
> variables. I have not yet had a need for such an implementation, and
> since it falls short of a true generic for_each_set_clump function, I
> have decided to forgo such an implementation for now.
>
> In addition, the bitmap_get_value8 and bitmap_set_value8 functions are
> introduced to get and set 8-bit values respectively. Their use is based
> on the behavior suggested in the patchset version 4 review.

Nice-looking code.

> drivers/gpio/gpio-104-dio-48e.c | 73 ++++++--------------
> drivers/gpio/gpio-104-idi-48.c | 37 +++-------
> drivers/gpio/gpio-gpio-mm.c | 73 ++++++--------------
> drivers/gpio/gpio-pci-idio-16.c | 75 ++++++++------------
> drivers/gpio/gpio-pcie-idio-24.c | 111 +++++++++++-------------------
> drivers/gpio/gpio-ws16c48.c | 72 ++++++-------------
> include/asm-generic/bitops/find.h | 14 ++++
> include/linux/bitops.h | 5 ++
> lib/find_bit.c | 81 ++++++++++++++++++++++
> lib/test_bitmap.c | 65 +++++++++++++++++
> 10 files changed, 307 insertions(+), 299 deletions(-)

It's a shame that it doesn't actually dercease the kernel line count,
but there are other benefits.

The patches are missing the hoped-for acks, but I think you maintain
most/all of those drivers.

Do we have any expectation that these facilities will be used by
anything other than GPIO? If not then perhaps they should be sited
within drivers/gpio (presumably as a standalone module) until such a
need is found?

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