riscv: Add qspinlock/qrwlock

From: Guo Ren <guoren@linux.alibaba.com>

Current riscv is still using baby spinlock implementation. It'll cause
fairness and cache line bouncing problems. Many people are involved
and pay the efforts to improve it:

 - The first version of patch was made in 2019.1:
   https://lore.kernel.org/linux-riscv/20190211043829.30096-...

 - The second version was made in 2020.11:
   https://lore.kernel.org/linux-riscv/1606225437-22948-2-gi...

 - A good discussion at Platform HSC.2021-03-08:
   https://drive.google.com/drive/folders/1ooqdnIsYx7XKor5O1...

Hope your comments and Tested-by or Co-developed-by or Reviewed-by ...

Let's kick the qspinlock into riscv right now (Also for the
architectures which doesn't have short atmoic xchg instructions.)

Change V3:
 - Fixup short-xchg asm code (slli -> slliw, srli -> srliw)
 - Coding convention by Peter Zijlstra's advices 

Change V2:
 - Coding convention in cmpxchg.h
 - Re-implement short xchg
 - Remove char & cmpxchg implementations

V1: (by michael)

Guo Ren (3):
  riscv: cmpxchg.h: Cleanup unused code
  riscv: cmpxchg.h: Merge macros
  riscv: cmpxchg.h: Implement xchg for short

Michael Clark (1):
  riscv: Convert custom spinlock/rwlock to generic qspinlock/qrwlock

 arch/riscv/Kconfig                      |   2 +
 arch/riscv/include/asm/Kbuild           |   3 +
 arch/riscv/include/asm/cmpxchg.h        | 211 ++++++------------------
 arch/riscv/include/asm/spinlock.h       | 126 +-------------
 arch/riscv/include/asm/spinlock_types.h |  15 +-
 5 files changed, 58 insertions(+), 299 deletions(-)

-- 
2.17.1