[RFC PATCH v3 0/7] riscv: add initial sdext support

[Chao Liu <chao.liu.zevorn@gmail.com>]

Hi,

Per Daniel's review feedback, this v3 series is based on Alistair's
riscv-to-apply.next branch [3]. It depends on Max Chou's patch
"target/riscv: Use the tb->cs_bqse as the extend tb flags."
(not included in this series; apply it first) [2].

It is based on RISC-V Debug Specification 1.0 [1].

It introduces the sdext/sdtrig config bits, DCSR/DPC/DSCRATCH state,
Debug Mode enter/leave helpers, DRET, EBREAK entry, single-step, and
trigger action=debug mode.

To reduce review load, this series focuses on the Sdext features first.
The Debug Module (DM) and related flows will follow in a later series.

Changes in v3:
- Rebase onto Alistair's riscv-to-apply.next branch.
- Depend on Max Chou's patch "target/riscv: Use the tb->cs_bqse as
  the extend tb flags." (not included; apply it first) [2].
- Patch 2: default sdext to false in riscv_cpu_extensions[].

Changes in v2:
- Drop the RHCT expected AML update from this series.
- Replace the split sdext/sdtrig config bits patch with deprecating the
  'debug' CPU property.
- Rebase and update patch subjects to target/riscv prefix.

Changes in v1:
- Debug Mode entry/exit updates DCSR/DPC and restores execution via DRET.
- EBREAK honors DCSR ebreak bits and enters Debug Mode when enabled.
- Single-step uses DCSR.STEP with a TB flag and a helper at TB exit.
  It references Max Chou's patch "target/riscv: Use the tb->cs_bqse as
  the extend tb flags." [2].
- Sdtrig supports action=debug mode for mcontrol/mcontrol6 and reports
  inst-count triggers in tinfo.

Differences vs Debug Spec (known gaps):
- No Debug Module (no DMI, dmcontrol/dmstatus, haltreq/resumereq).
- No debug ROM, program buffer, abstract commands, or SBA.
- Resume is modeled by leaving Debug Mode at cpu_exec_enter.
- Step/exception ordering is simplified: if the stepped instruction
  traps, the normal exception is taken and Debug Mode is not forced.
- Several DCSR fields are not fully modeled (stopcount/stoptime, etc).

Roadmap (next stage, DM focus):
1) Add a DM core with DMI access and hart state tracking.
2) Implement halt/resume handshake and move Debug Mode transitions
   under DM control.
3) Add debug ROM, program buffer, and abstract commands for GPR/CSR
   and memory access.
4) Add SBA if required by tooling.
5) Tighten ordering rules for step/exception/trigger priorities.


References:
[1] https://github.com/riscv/riscv-debug-spec/releases/tag/1.0
[2] https://lore.kernel.org/qemu-devel/20260108132631.9429-6-max.chou@sifive.com/
[3] https://github.com/alistair23/qemu/tree/riscv-to-apply.next


Thanks,
Chao


Chao Liu (6):
  target/riscv: add sdext debug CSRs state
  target/riscv: add sdext Debug Mode helpers
  target/riscv: add dret instruction
  target/riscv: add sdext enter Debug Mode on ebreak
  target/riscv: add sdext single-step support
  target/riscv: add sdtrig trigger action=debug mode

Daniel Henrique Barboza (1):
  target/riscv: deprecate 'debug' CPU property

 docs/about/deprecated.rst                     |   7 +
 include/exec/translation-block.h              |   4 +-
 target/riscv/cpu.c                            |  61 ++++++++-
 target/riscv/cpu.h                            |   9 ++
 target/riscv/cpu_bits.h                       |  33 +++++
 target/riscv/cpu_cfg_fields.h.inc             |   3 +-
 target/riscv/cpu_helper.c                     |  93 +++++++++++++
 target/riscv/csr.c                            | 128 +++++++++++++++++-
 target/riscv/debug.c                          |  58 +++++++-
 target/riscv/helper.h                         |   3 +
 target/riscv/insn32.decode                    |   1 +
 .../riscv/insn_trans/trans_privileged.c.inc   |  24 +++-
 target/riscv/machine.c                        |  44 ++++--
 target/riscv/op_helper.c                      |  72 ++++++++++
 target/riscv/tcg/tcg-cpu.c                    |  21 ++-
 target/riscv/translate.c                      |  15 +-
 16 files changed, 548 insertions(+), 28 deletions(-)

-- 
2.52.0