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(+)