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[00/17] Introduce and use generic parity32/64 helper

Message ID 20250223164217.2139331-1-visitorckw@gmail.com (mailing list archive)
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Series Introduce and use generic parity32/64 helper | expand

Message

Kuan-Wei Chiu Feb. 23, 2025, 4:42 p.m. UTC 
Several parts of the kernel contain redundant implementations of parity
calculations for 32-bit and 64-bit values. Introduces generic
parity32() and parity64() helpers in bitops.h, providing a standardized
and optimized implementation.  

Subsequent patches refactor various kernel components to replace
open-coded parity calculations with the new helpers, reducing code
duplication and improving maintainability.  

Co-developed-by: Yu-Chun Lin <eleanor15x@gmail.com>
Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com>
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>

Kuan-Wei Chiu (17):
  bitops: Add generic parity calculation for u32
  bitops: Add generic parity calculation for u64
  x86: Replace open-coded parity calculation with parity8()
  media: media/test_drivers: Replace open-coded parity calculation with
    parity8()
  media: pci: cx18-av-vbi: Replace open-coded parity calculation with
    parity8()
  media: saa7115: Replace open-coded parity calculation with parity8()
  serial: max3100: Replace open-coded parity calculation with parity8()
  lib/bch: Replace open-coded parity calculation with parity32()
  Input: joystick - Replace open-coded parity calculation with
    parity32()
  net: ethernet: oa_tc6: Replace open-coded parity calculation with
    parity32()
  wifi: brcm80211: Replace open-coded parity calculation with parity32()
  rm/bridge: dw-hdmi: Replace open-coded parity calculation with
    parity32()
  mtd: ssfdc: Replace open-coded parity calculation with parity32()
  fsi: i2cr: Replace open-coded parity calculation with parity32()
  fsi: i2cr: Replace open-coded parity calculation with parity64()
  Input: joystick - Replace open-coded parity calculation with
    parity64()
  nfp: bpf: Replace open-coded parity calculation with parity64()

 arch/x86/kernel/bootflag.c                    | 18 ++------
 drivers/fsi/fsi-master-i2cr.c                 | 18 ++------
 .../drm/bridge/synopsys/dw-hdmi-ahb-audio.c   |  8 +---
 drivers/input/joystick/grip_mp.c              | 17 +-------
 drivers/input/joystick/sidewinder.c           | 24 +++--------
 drivers/media/i2c/saa7115.c                   | 12 +-----
 drivers/media/pci/cx18/cx18-av-vbi.c          | 12 +-----
 .../media/test-drivers/vivid/vivid-vbi-gen.c  |  8 +---
 drivers/mtd/ssfdc.c                           | 17 +-------
 drivers/net/ethernet/netronome/nfp/nfp_asm.c  |  7 +--
 drivers/net/ethernet/oa_tc6.c                 | 19 ++------
 .../broadcom/brcm80211/brcmsmac/dma.c         | 16 +------
 drivers/tty/serial/max3100.c                  |  3 +-
 include/linux/bitops.h                        | 43 +++++++++++++++++++
 lib/bch.c                                     | 14 +-----
 15 files changed, 74 insertions(+), 162 deletions(-)

Comments

Uros Bizjak Feb. 23, 2025, 8:25 p.m. UTC | #1 
On 23. 02. 25 17:42, Kuan-Wei Chiu wrote:
> Several parts of the kernel contain redundant implementations of parity
> calculations for 32-bit and 64-bit values. Introduces generic
> parity32() and parity64() helpers in bitops.h, providing a standardized
> and optimized implementation.
> 
> Subsequent patches refactor various kernel components to replace
> open-coded parity calculations with the new helpers, reducing code
> duplication and improving maintainability.

Please note that GCC (and clang) provide __builtin_parity{,l,ll}() 
family of builtin functions. Recently, I have tried to use this builtin 
in a couple of places [1], [2], but I had to retract the patches, 
because __builtin functions aren't strictly required to be inlined and 
can generate a library call [3].

As explained in [2], the compilers are able to emit optimized 
target-dependent code (also automatically using popcnt insn when 
avaialble), so ideally the generic parity64() and parity32() would be 
implemented using __builtin_parity(), where the generic library would 
provide a fallback __paritydi2() and __paritysi2() functions, otherwise 
provided by the compiler support library.

For x86, we would like to exercise the hardware parity calculation or 
optimized code sequences involving HW parity calculation, as shown in 
[1] and [2].

[1] https://lore.kernel.org/lkml/20250129205746.10963-1-ubizjak@gmail.com/

[2] https://lore.kernel.org/lkml/20250129154920.6773-2-ubizjak@gmail.com/

[3] 
https://lore.kernel.org/linux-mm/CAKbZUD0N7bkuw_Le3Pr9o1V2BjjcY_YiLm8a8DPceubTdZ00GQ@mail.gmail.com/

Thanks,
Uros.