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Date:   Sat, 5 Oct 2019 14:46:40 -0400
From:   William Breathitt Gray <vilhelm.gray@gmail.com>
To:     linus.walleij@linaro.org, bgolaszewski@baylibre.com
Cc:     akpm@linux-foundation.org, linux-gpio@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
        andriy.shevchenko@linux.intel.com, linux@rasmusvillemoes.dk,
        yamada.masahiro@socionext.com,
        linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org,
        geert@linux-m68k.org, preid@electromag.com.au, lukas@wunner.de,
        sean.nyekjaer@prevas.dk, morten.tiljeset@prevas.dk
Subject: Re: [PATCH v15 00/14] Introduce the for_each_set_clump8 macro
Message-ID: <20191005184640.GA117093@icarus>
References: <cover.1570299719.git.vilhelm.gray@gmail.com>
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On Sat, Oct 05, 2019 at 02:36:54PM -0400, William Breathitt Gray wrote:
> Changes in v15:
>   - Move find_next_clump8 to lib/find_bit.c since it requires round_down
>     (I want this to be static inline like the others, but I need help)
>   - Utilize for_each_set_clump8 in pisosr, max3191x, and pca953x
> 
> 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.
> 
> William Breathitt Gray (14):
>   bitops: Introduce the for_each_set_clump8 macro
>   lib/test_bitmap.c: Add for_each_set_clump8 test cases
>   gpio: 104-dio-48e: Utilize for_each_set_clump8 macro
>   gpio: 104-idi-48: Utilize for_each_set_clump8 macro
>   gpio: gpio-mm: Utilize for_each_set_clump8 macro
>   gpio: ws16c48: Utilize for_each_set_clump8 macro
>   gpio: pci-idio-16: Utilize for_each_set_clump8 macro
>   gpio: pcie-idio-24: Utilize for_each_set_clump8 macro
>   gpio: uniphier: Utilize for_each_set_clump8 macro
>   gpio: 74x164: Utilize the for_each_set_clump8 macro
>   thermal: intel: intel_soc_dts_iosf: Utilize for_each_set_clump8 macro
>   gpio: pisosr: Utilize the for_each_set_clump8 macro
>   gpio: max3191x: Utilize the for_each_set_clump8 macro
>   gpio: pca953x: Utilize the for_each_set_clump8 macro
> 
>  drivers/gpio/gpio-104-dio-48e.c            |  73 ++++----------
>  drivers/gpio/gpio-104-idi-48.c             |  36 ++-----
>  drivers/gpio/gpio-74x164.c                 |  19 ++--
>  drivers/gpio/gpio-gpio-mm.c                |  73 ++++----------
>  drivers/gpio/gpio-max3191x.c               |  19 ++--
>  drivers/gpio/gpio-pca953x.c                |  17 ++--
>  drivers/gpio/gpio-pci-idio-16.c            |  75 +++++---------
>  drivers/gpio/gpio-pcie-idio-24.c           | 109 ++++++++-------------
>  drivers/gpio/gpio-pisosr.c                 |  12 +--
>  drivers/gpio/gpio-uniphier.c               |  16 ++-
>  drivers/gpio/gpio-ws16c48.c                |  73 ++++----------
>  drivers/thermal/intel/intel_soc_dts_iosf.c |  29 +++---
>  drivers/thermal/intel/intel_soc_dts_iosf.h |   2 -
>  include/asm-generic/bitops/find.h          |  50 ++++++++++
>  include/linux/bitops.h                     |   5 +
>  lib/find_bit.c                             |  14 +++
>  lib/test_bitmap.c                          |  65 ++++++++++++
>  17 files changed, 325 insertions(+), 362 deletions(-)
> 
> -- 
> 2.23.0

This patchset only implements for_each_set_clump8 which restricts the
looping to 8 bits at a time. The drivers/gpio/gpio-thunderx.c file has a
set_multiple callback that loops 64 bits at a time. That would be one
case where a more general for_each_set_clump macro would be useful.

However, we can focus on the simpler for_each_set_clump8 macro for now
since looping by 8 bits at a time is the most common situation.

William Breathitt Gray