[v3,0/4] Non-const bitfield helpers

Message

Geert Uytterhoeven Feb. 14, 2025, 1:55 p.m. UTC

Hi all,

This is an updated subset of a patch series I sent more than 3 years
ago[2].

<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 v2[1]:
  - New patch "[PATCH v3 1/4] bitfield: Drop underscores from macro
    parameters",
  - Add Acked-by,
  - Drop underscores from macro parameters,
  - Use __auto_type where possible,
  - Correctly cast reg to the mask type,
  - Introduces __val and __reg intermediates to simplify the actual
    operation,
  - Drop unneeded parentheses,
  - Clarify having both FIELD_{GET,PREP}() and field_{get,prep}(),

Changes compared to v1[2]:
  - 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 four patches through the Renesas tree, and provide an
immutable branch with the first two patches for the interested parties.

Thanks for your comments!

[1] "[PATCH v2 0/3] Non-const bitfield helpers"
    https://lore.kernel.org/all/[e-mail]
[2] "[PATCH 00/17] Non-const bitfield helper conversions"
    https://lore.kernel.org/all/[e-mail]

Geert Uytterhoeven (4):
  bitfield: Drop underscores from macro parameters
  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                      | 122 ++++++++++++------
 sound/usb/mixer_quirks.c                      |   4 -
 13 files changed, 97 insertions(+), 92 deletions(-)