linux-kernel - [PATCH v7 0/4] riscv: Use Kconfig to set unaligned access speed

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Message-Id: <20240306-disable_misaligned_probe_config-v7-0-6c90419e7a96@rivosinc.com>
Date: Wed, 06 Mar 2024 12:00:00 -0800
From: Charlie Jenkins <charlie@...osinc.com>
To: Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Jisheng Zhang <jszhang@...nel.org>, Evan Green <evan@...osinc.com>, 
 Clément Léger <cleger@...osinc.com>, 
 Eric Biggers <ebiggers@...nel.org>, 
 Elliot Berman <quic_eberman@...cinc.com>, Charles Lohr <lohr85@...il.com>, 
 Conor Dooley <conor.dooley@...rochip.com>
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 Charlie Jenkins <charlie@...osinc.com>
Subject: [PATCH v7 0/4] riscv: Use Kconfig to set unaligned access speed

If the hardware unaligned access speed is known at compile time, it is
possible to avoid running the unaligned access speed probe to speedup
boot-time.

Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
---
Changes in v7:
- Fix check_unaligned_access_emulated_all_cpus to return false when any
  cpu has emulated accesses
- Fix wording in Kconfig (Conor)
- Link to v6: https://lore.kernel.org/r/20240301-disable_misaligned_probe_config-v6-0-612ebd69f430@rivosinc.com

Changes in v6:
- Consolidate Kconfig into 4 options (probe, emulated, slow,
  efficient)
- Change the behavior of "emulated" to allow hwprobe to return "slow" if
  unaligned accesses are not emulated by the kernel
- With this consolidation, check_unaligned_access_emulated is able to be
  moved back into the original file (traps_misaligned.c)
- Link to v5: https://lore.kernel.org/r/20240227-disable_misaligned_probe_config-v5-0-b6853846e27a@rivosinc.com

Changes in v5:
- Clarify Kconfig options from Conor's feedback
- Use "unaligned" instead of "misaligned" in introduced file/function.
  This is a bit hard to standardize because the riscv manual says
  "misaligned" but the existing Linux configs say "unaligned".
- Link to v4: https://lore.kernel.org/r/20240216-disable_misaligned_probe_config-v4-0-dc01e581c0ac@rivosinc.com

Changes in v4:
- Add additional Kconfig options for the other unaligned access speeds
- Link to v3: https://lore.kernel.org/r/20240202-disable_misaligned_probe_config-v3-0-c44f91f03bb6@rivosinc.com

Changes in v3:
- Revert change to csum (Eric)
- Change ifndefs for ifdefs (Eric)
- Change config in Makefile (Elliot/Eric)
- Link to v2: https://lore.kernel.org/r/20240201-disable_misaligned_probe_config-v2-0-77c368bed7b2@rivosinc.com

Changes in v2:
- Move around definitions to reduce ifdefs (Clément)
- Make RISCV_MISALIGNED depend on !HAVE_EFFICIENT_UNALIGNED_ACCESS
  (Clément)
- Link to v1: https://lore.kernel.org/r/20240131-disable_misaligned_probe_config-v1-0-98d155e9cda8@rivosinc.com

---
Charlie Jenkins (4):
      riscv: lib: Introduce has_fast_unaligned_access function
      riscv: Only check online cpus for emulated accesses
      riscv: Decouple emulated unaligned accesses from access speed
      riscv: Set unaligned access speed at compile time

 arch/riscv/Kconfig                         |  60 ++++--
 arch/riscv/include/asm/cpufeature.h        |  31 ++--
 arch/riscv/kernel/Makefile                 |   4 +-
 arch/riscv/kernel/cpufeature.c             | 255 --------------------------
 arch/riscv/kernel/sys_hwprobe.c            |  15 ++
 arch/riscv/kernel/traps_misaligned.c       |  17 +-
 arch/riscv/kernel/unaligned_access_speed.c | 282 +++++++++++++++++++++++++++++
 arch/riscv/lib/csum.c                      |   7 +-
 8 files changed, 378 insertions(+), 293 deletions(-)
---
base-commit: 6613476e225e090cc9aad49be7fa504e290dd33d
change-id: 20240131-disable_misaligned_probe_config-043aea375f93
-- 
- Charlie