linux-kernel - [PATCH v2 0/3] Non-const bitfield helpers

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Message-ID: <cover.1738329458.git.geert+renesas@glider.be>
Date: Fri, 31 Jan 2025 14:46:50 +0100
From: Geert Uytterhoeven <geert+renesas@...der.be>
To: Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>,
	Nicolas Ferre <nicolas.ferre@...rochip.com>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Claudiu Beznea <claudiu.beznea@...on.dev>,
	Giovanni Cabiddu <giovanni.cabiddu@...el.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S . Miller" <davem@...emloft.net>,
	Linus Walleij <linus.walleij@...aro.org>,
	Bartosz Golaszewski <brgl@...ev.pl>,
	Joel Stanley <joel@....id.au>,
	Andrew Jeffery <andrew@...econstruct.com.au>,
	Crt Mori <cmo@...exis.com>,
	Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Jacky Huang <ychuang3@...oton.com>,
	Shan-Chun Hung <schung@...oton.com>,
	Yury Norov <yury.norov@...il.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.com>,
	Johannes Berg <johannes@...solutions.net>,
	Jakub Kicinski <kuba@...nel.org>,
	Alex Elder <elder@...e.org>
Cc: linux-clk@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-renesas-soc@...r.kernel.org,
	linux-crypto@...r.kernel.org,
	qat-linux@...el.com,
	linux-gpio@...r.kernel.org,
	linux-aspeed@...ts.ozlabs.org,
	linux-iio@...r.kernel.org,
	linux-sound@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Geert Uytterhoeven <geert+renesas@...der.be>
Subject: [PATCH v2 0/3] Non-const bitfield helpers

	Hi all,

This is an updated subset of a patch series I sent more than 3 years
ago[1].

<linux/bitfield.h> contains various helpers for accessing bitfields, as
typically used in hardware registers for memory-mapped I/O blocks.
These helpers ensure type safety, and deduce automatically shift values
from mask values, avoiding mistakes due to inconsistent shifts and
masks, and leading to a reduction in source code size.

The existing FIELD_{GET,PREP}() macros are limited to compile-time
constants.  However, it is very common to prepare or extract bitfield
elements where the bitfield mask is not a compile-time constant.
To avoid this limitation, the AT91 clock driver introduced its own
field_{prep,get}() macros.  Hence my v1 series aimed to make them
available for general use, and convert several drivers to the existing
FIELD_{GET,PREP}() and the new field_{get,prep}() helpers.

Due to some pushback (mostly centered around using the typed
{u*,be*,le*,...}_get_bits() macros instead, which of course would
require making them work with non-constant masks first, too), this
series was never applied, and became buried deep in my TODO haystack...
However, several people still liked the idea: since v1, multiple copies
of the field_{prep,get}() macros appeared upstream, and one more is
queued for v6.15.

Hence I think it's time to revive and consolidate...

Changes compared to v1:
  - Cast val resp. reg to the mask type,
  - Fix 64-bit use on 32-bit architectures,
  - Convert new upstream users:
      - drivers/crypto/intel/qat/qat_common/adf_gen4_pm_debugfs.c
      - drivers/gpio/gpio-aspeed.c
      - drivers/iio/temperature/mlx90614.c
      - drivers/pinctrl/nuvoton/pinctrl-ma35.c
      - sound/usb/mixer_quirks.c
  - Convert new user queued in renesas-devel for v6.15:
      - drivers/soc/renesas/rz-sysc.c
  - Drop the last 14 RFC patches.
    They can be updated/resubmitted/applied later.

I can take all three patches through the Renesas tree, and provide an
immutable branch with the first patch for ther interested parties.

Thanks for your comments!

[1] "[PATCH 00/17] Non-const bitfield helper conversions"
    https://lore.kernel.org/all/cover.1637592133.git.geert+renesas@glider.be

Geert Uytterhoeven (3):
  bitfield: Add non-constant field_{prep,get}() helpers
  clk: renesas: Use bitfield helpers
  soc: renesas: Use bitfield helpers

 drivers/clk/at91/clk-peripheral.c             |  1 +
 drivers/clk/at91/pmc.h                        |  3 --
 drivers/clk/renesas/clk-div6.c                |  6 ++--
 drivers/clk/renesas/rcar-gen3-cpg.c           | 15 +++-----
 drivers/clk/renesas/rcar-gen4-cpg.c           |  9 ++---
 .../qat/qat_common/adf_gen4_pm_debugfs.c      |  8 +----
 drivers/gpio/gpio-aspeed.c                    |  5 +--
 drivers/iio/temperature/mlx90614.c            |  5 +--
 drivers/pinctrl/nuvoton/pinctrl-ma35.c        |  4 ---
 drivers/soc/renesas/renesas-soc.c             |  4 +--
 drivers/soc/renesas/rz-sysc.c                 |  3 +-
 include/linux/bitfield.h                      | 34 +++++++++++++++++++
 sound/usb/mixer_quirks.c                      |  4 ---
 13 files changed, 52 insertions(+), 49 deletions(-)

-- 
2.43.0

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds