[PATCH v4 0/3] Add support for RISC-V Smrnmi extension

[Nylon Chen]

Sorry, please ignore this v4 series. It was sent before I had fully
reviewed the ongoing discussion, particularly Nick's comments and
Evgeny's Smrnmi series for Ascalon.

I will take time to review their work carefully and send a revised
version that better aligns with the direction of the discussion.

Apologies for the noise.

Thanks,
Nylon

Nylon Chen <nylon.chen at sifive.com> 於 2026年3月13日週五 下午9:39寫道：
>
> This patch series adds support for the RISC-V Smrnmi (Resumable
> Non-Maskable Interrupts) extension to OpenSBI.
>
> 1. PATCH 1/3: Add Smrnmi extension detection
>    - Defines Smrnmi CSR registers (MNSCRATCH, MNEPC, MNCAUSE, MNSTATUS)
>    - Defines MNSTATUS bit fields (NMIE, MNPV, MNPELP, MNPP)
>    - Registers the Smrnmi extension in hart extension enumeration
>
> 2. PATCH 2/3: Enable Smrnmi extension handler
>    - Implements rnmi_vector_init() as a static function in sbi_hart.c
>    - Sets MNSCRATCH to the scratch pointer (same role as MSCRATCH)
>    - Adds platform operation set_rnmi_trap_vector() for trap vector programming
>    - Adds suspend/resume support for RNMI CSRs (MNSCRATCH, MNSTATUS)
>    - Calls rnmi_vector_init() at the end of sbi_hart_init()
>    - Note: Does not yet enable RNMI; trap vector setup deferred to Patch 3
>
> 3. PATCH 3/3: Add common NMI trap handler
>    - Implements sbi_rnmi_vector assembly entry point in fw_base.S
>    - Checks MNSTATUS.MNPP to distinguish S/U-mode vs M-mode interrupts
>    - Uses scratch area for S/U-mode interrupts
>    - Reuses existing M-mode stack for M-mode interrupts (nested RNMI)
>    - Implements default sbi_rnmi_trap_handler() in C (marked __attribute__((weak)))
>    - Completes rnmi_vector_init() with platform hook call and NMIE enablement
>
> Changes in v4:
>  - Added MNSTATUS.MNPELP bit definition (for Zicfilp extension)
>  - Made rnmi_vector_init() a static function and removed global declaration
>  - Moved rnmi_vector_init() call from sbi_init.c to end of sbi_hart_init()
>  - Changed set_rnmi_trap_vector() parameter type from uintptr_t to unsigned long
>  - Changed platform hook requirement from "should" to "must" in documentation
>  - Simplified MNSCRATCH setup: directly use scratch pointer instead of allocating
>    separate RNMI context (addresses Radim's feedback on stack space)
>  - Rewrote sbi_rnmi_vector to check MNSTATUS.MNPP and reuse M-mode stack for
>    nested RNMI (addresses Radim's feedback on M-mode stack reuse)
>  - Removed RNMI_SAVE_REGS/RNMI_RESTORE_REGS macros in favor of explicit
>    register save/restore for better control
>  - Added sbi_rnmi_trap_handler() declaration in sbi_trap.h
>  - Changed printf format from %016lx to PRILX macro for 32/64-bit compatibility
>  - Fixed patch structure: Patch 2 now only sets up MNSCRATCH; Patch 3 completes
>    the initialization with trap vector setup and NMIE enablement (ensures each
>    patch can be compiled independently)
>  - Marked sbi_rnmi_trap_handler() as __attribute__((weak)) to allow platform override
>
> Changes in v3:
>  - Split single patch into three-patch series per Anup's feedback:
>   * PATCH 1: Add Smrnmi extension detection (without enabling NMI)
>   * PATCH 2: Enable Smrnmi extension handler
>   * PATCH 3: Add common NMI trap handler in fw_base.S
>  - Added platform abstraction via set_rnmi_trap_vector() callback
>  - Added per-HART RNMI context allocation
>  - Added suspend/resume support for RNMI CSRs
>
> Changes in v2:
>  - Remove hart_smrnmi_get_allowed() and use sbi_hart_has_extension() for
>    Smrnmi detection
>
> Co-developed-by: Zong Li <zong.li at sifive.com>
> Signed-off-by: Zong Li <zong.li at sifive.com>
> Suggested-by: Nick Hu <nick.hu at sifive.com>
> Suggested-by: Samuel Holland <samuel.holland at sifive.com>
> Signed-off-by: Nylon Chen <nylon.chen at sifive.com>
> Signed-off-by: Yong-Xuan Wang <yongxuan.wang at sifive.com>
>
> Nylon Chen (3):
>   lib: sbi: Add Smrnmi extension detection
>   lib: sbi: Enable Smrnmi extension handler
>   firmware: fw_base.S: Add common NMI trap handler
>
>  firmware/fw_base.S           | 141 +++++++++++++++++++++++++++++++++++
>  include/sbi/riscv_encoding.h |  12 +++
>  include/sbi/sbi_hart.h       |   2 +
>  include/sbi/sbi_platform.h   |   8 ++
>  include/sbi/sbi_trap.h       |  22 +++++-
>  lib/sbi/sbi_hart.c           |  54 +++++++++++++-
>  lib/sbi/sbi_hsm.c            |  14 ++++
>  lib/sbi/sbi_trap.c           |  17 +++++
>  8 files changed, 267 insertions(+), 3 deletions(-)
>
> --
> 2.43.7
>