Re: [PATCH v5 0/6] Privilege version update

[Alistair Francis]

On Fri, Mar 4, 2022 at 4:59 AM Atish Patra <atishp@rivosinc.com> wrote:
>
> RISC-V International (RVI) has ratified many RISC-V ISA extensions 
> recently[1].
> The privileged specification version is also upgraded to v1.12. It means
> certain CSRs introduced in v1.12 should only be accessible only if the
> priv specification version supported is equal or greater than v1.12.
> Doing this check in predicate function is not scalable as there will be
> new CSRs introduced in the future versions of the privileged specification.
>
> This series tries to address this problem by adding a field in the csr_ops
> which can be checked in csrrw function before invoking the predicate function.
> To keep the code churn to minimum, it is assumed that the minimum version of
> the privilege version supported for any CSR is v1.10 unless specified
> explicitly in the csr_ops table. Any new CSRs introduced in v1.12 have been
> updated accordingly.
>
> This will work fine for any ratified extensions. However, it is bit unclear
> what should be done for the stable draft extensions. My suggestion is not
> to update the priv field in the CSR ops table until the extension is
> marked experimental (i.e. not frozen/ratified). Once the extension is
> ratified and graduated from experimental to available stage, the privileged
> spec version should be updated in the csr table if required. I am open to
> other suggestions as well.
>
> [1] https://wiki.riscv.org/display/TECH/Recently+Ratified+Extensions
>
> Changes from v4->v5:
> 1. Rebased on top of riscv-to-apply.next
>
> Changes from v3->v4:
> 1. Added reviewed-by tags.
> 2. Improved the commit text in PATCH 3 & 6.
>
> Changes from v2->v3:
> 1. Only update the bits defined in *envcfg CSR
>
> Changes from v1->v2:
> 1. Unified both [m/h]envcfg & [m/h]envcfgh into one.
> 2. Changed the priv spec version enumeration
> 3. Improved csr_ops table to provide better redability.
> 4. Fixed the compilation error for CONFIG_USER_ONLY
> 5. Rebased on top of the AIA series.
>
> Atish Patra (6):
> target/riscv: Define simpler privileged spec version numbering
> target/riscv: Add the privileged spec version 1.12.0
> target/riscv: Introduce privilege version field in the CSR ops.
> target/riscv: Add support for mconfigptr
> target/riscv: Add *envcfg* CSRs support
> target/riscv: Enable privileged spec version 1.12

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

>
> target/riscv/cpu.c      |   8 +-
> target/riscv/cpu.h      |  15 ++-
> target/riscv/cpu_bits.h |  40 ++++++++
> target/riscv/csr.c      | 217 +++++++++++++++++++++++++++++++++-------
> target/riscv/machine.c  |  23 +++++
> 5 files changed, 263 insertions(+), 40 deletions(-)
>
> --
> 2.30.2
>
>