[RFC PATCH v6 0/2] arch: riscv: cpu: Add callback to init each core

[Green Wan]

Add a callback interface, harts_early_init() to perform proprietary or
customized CRSs configuration for each hart. harts_early_init() is placed
after stack of harts are initialized and before main boot hart is picked up.
Several conditions should be aware of or avoided are listed:

  - cannot access gd
    At the moment, gd hasn't initialized yet.

  - all operations in harts_early_init() should only affect core itself
    For example, the operations for board level should be moved to mach_xxx()
    or board_init_xxx() functions instead.

  - Common resource need protection if multicore
    Since all harts might enter harts_early_init() in parallel, common
    resource need a mechanism to handle race condition.

  - A reference implementation is added in ./arch/riscv/cpu/cpu.c
    The implementation is declared with '__weak' and can be overridden.

Changelogs:
v6
  - revised the description in both of commit message and comment [1/2]
  - moved the implementation of harts_early_init() in [2/2] from
    board/sifive/unmatched/spl.c to arch/riscv/cpu/fu740/spl.c. and revised
    commit message
v5
  - rename riscv_hart_early_init to harts_early_init
  - rephrase dummy for harts_early_init() to callback but keep current
    comments not specific for customizing CSRs only.
  - Fix nit in [2/2] and add reviewed-by
v4
  - Revising the comments for riscv_hart_early_init() in [1/2]
  - Remove unnecessary braces and add reviewed-by in [2/2]

Green Wan (2):
  arch: riscv: cpu: Add callback to init each core
  board: sifive: unmatched: clear feature disable CSR

 arch/riscv/cpu/cpu.c       | 11 +++++++++++
 arch/riscv/cpu/fu740/spl.c | 15 +++++++++++++++
 arch/riscv/cpu/start.S     |  8 ++++++++
 3 files changed, 34 insertions(+)

-- 
2.31.0