Re: [PATCH v2 01/10] target/riscv/cpu.c: add zicntr extension flag

[Alistair Francis <alistair23@gmail.com>]

On Fri, Oct 6, 2023 at 11:23 PM Daniel Henrique Barboza
<dbarboza@ventanamicro.com> wrote:
>
> zicntr is the Base Counters and Timers extension described in chapter 12
> of the unprivileged spec. It describes support for RDCYCLE, RDTIME and
> RDINSTRET.
>
> QEMU already implements it way before it was a discrete extension.
> zicntr is part of the RVA22 profile, so let's add it to QEMU to make the
> future profile implementation flag complete.
>
> Given than it represents an already existing feature, default it to
> 'true'. Change the realize() time validation to disable it in case its
> dependency (icsr) isn't present.

What happens if a user disables this though?

Alistair

>
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
> ---
>  target/riscv/cpu.c         | 7 +++++++
>  target/riscv/cpu_cfg.h     | 1 +
>  target/riscv/tcg/tcg-cpu.c | 4 ++++
>  3 files changed, 12 insertions(+)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index 521bb88538..8783a415b1 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -79,6 +79,7 @@ const RISCVIsaExtData isa_edata_arr[] = {
>      ISA_EXT_DATA_ENTRY(zicbom, PRIV_VERSION_1_12_0, ext_icbom),
>      ISA_EXT_DATA_ENTRY(zicboz, PRIV_VERSION_1_12_0, ext_icboz),
>      ISA_EXT_DATA_ENTRY(zicond, PRIV_VERSION_1_12_0, ext_zicond),
> +    ISA_EXT_DATA_ENTRY(zicntr, PRIV_VERSION_1_12_0, ext_icntr),
>      ISA_EXT_DATA_ENTRY(zicsr, PRIV_VERSION_1_10_0, ext_icsr),
>      ISA_EXT_DATA_ENTRY(zifencei, PRIV_VERSION_1_10_0, ext_ifencei),
>      ISA_EXT_DATA_ENTRY(zihintntl, PRIV_VERSION_1_10_0, ext_zihintntl),
> @@ -1265,6 +1266,12 @@ const RISCVCPUMultiExtConfig riscv_cpu_extensions[] = {
>      MULTI_EXT_CFG_BOOL("svnapot", ext_svnapot, false),
>      MULTI_EXT_CFG_BOOL("svpbmt", ext_svpbmt, false),
>
> +    /*
> +     * Always default true - we'll disable it during
> +     * realize() if needed.
> +     */
> +    MULTI_EXT_CFG_BOOL("zicntr", ext_icntr, true),
> +
>      MULTI_EXT_CFG_BOOL("zba", ext_zba, true),
>      MULTI_EXT_CFG_BOOL("zbb", ext_zbb, true),
>      MULTI_EXT_CFG_BOOL("zbc", ext_zbc, true),
> diff --git a/target/riscv/cpu_cfg.h b/target/riscv/cpu_cfg.h
> index 0e6a0f245c..671b8c7cb8 100644
> --- a/target/riscv/cpu_cfg.h
> +++ b/target/riscv/cpu_cfg.h
> @@ -62,6 +62,7 @@ struct RISCVCPUConfig {
>      bool ext_zksh;
>      bool ext_zkt;
>      bool ext_ifencei;
> +    bool ext_icntr;
>      bool ext_icsr;
>      bool ext_icbom;
>      bool ext_icboz;
> diff --git a/target/riscv/tcg/tcg-cpu.c b/target/riscv/tcg/tcg-cpu.c
> index 08b806dc07..df187bc143 100644
> --- a/target/riscv/tcg/tcg-cpu.c
> +++ b/target/riscv/tcg/tcg-cpu.c
> @@ -542,6 +542,10 @@ void riscv_cpu_validate_set_extensions(RISCVCPU *cpu, Error **errp)
>          cpu_cfg_ext_auto_update(cpu, CPU_CFG_OFFSET(ext_zksh), true);
>      }
>
> +    if (cpu->cfg.ext_icntr && !cpu->cfg.ext_icsr) {
> +        cpu->cfg.ext_icntr = false;
> +    }
> +
>      /*
>       * Disable isa extensions based on priv spec after we
>       * validated and set everything we need.
> --
> 2.41.0
>
>