Re: [PATCH v3] target/riscv: Add isa extenstion strings to the device tree

[Alistair Francis]

On Wed, Feb 23, 2022 at 8:39 AM Atish Patra <atishp@rivosinc.com> wrote:
>
> The Linux kernel parses the ISA extensions from "riscv,isa" DT
> property. It used to parse only the single letter base extensions
> until now. A generic ISA extension parsing framework was proposed[1]
> recently that can parse multi-letter ISA extensions as well.
>
> Generate the extended ISA string by appending  the available ISA extensions
> to the "riscv,isa" string if it is enabled so that kernel can process it.
>
> [1] https://lkml.org/lkml/2022/2/15/263
>
> Suggested-by: Heiko Stubner <heiko@sntech.de>
> Signed-off-by: Atish Patra <atishp@rivosinc.com>

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

Alistair

> ---
> Changes from v2->v3:
> 1. Used g_strconcat to replace snprintf & a max isa string length as
> suggested by Anup.
> 2. I have not included the Tested-by Tag from Heiko because the
> implementation changed from v2 to v3.
>
> Changes from v1->v2:
> 1. Improved the code redability by using arrays instead of individual check
> ---
>  target/riscv/cpu.c | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index b0a40b83e7a8..2c7ff6ef555a 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -34,6 +34,12 @@
>
>  /* RISC-V CPU definitions */
>
> +/* This includes the null terminated character '\0' */
> +struct isa_ext_data {
> +        const char *name;
> +        bool enabled;
> +};
> +
>  static const char riscv_exts[26] = "IEMAFDQCLBJTPVNSUHKORWXYZG";
>
>  const char * const riscv_int_regnames[] = {
> @@ -881,6 +887,28 @@ static void riscv_cpu_class_init(ObjectClass *c, void 
> *data)
>      device_class_set_props(dc, riscv_cpu_properties);
>  }
>
> +static void riscv_isa_string_ext(RISCVCPU *cpu, char **isa_str, int 
> max_str_len)
> +{
> +    char *old = *isa_str;
> +    char *new = *isa_str;
> +    int i;
> +    struct isa_ext_data isa_edata_arr[] = {
> +        { "svpbmt", cpu->cfg.ext_svpbmt   },
> +        { "svinval", cpu->cfg.ext_svinval },
> +        { "svnapot", cpu->cfg.ext_svnapot },
> +    };
> +
> +    for (i = 0; i < ARRAY_SIZE(isa_edata_arr); i++) {
> +        if (isa_edata_arr[i].enabled) {
> +            new = g_strconcat(old, "_", isa_edata_arr[i].name, NULL);
> +            g_free(old);
> +            old = new;
> +        }
> +    }
> +
> +    *isa_str = new;
> +}
> +
>  char *riscv_isa_string(RISCVCPU *cpu)
>  {
>      int i;
> @@ -893,6 +921,7 @@ char *riscv_isa_string(RISCVCPU *cpu)
>          }
>      }
>      *p = '\0';
> +    riscv_isa_string_ext(cpu, &isa_str, maxlen);
>      return isa_str;
>  }
>
> --
> 2.30.2
>
>