Re: [PATCH v2] target/riscv: Add isa extenstion strings to the device tree

[Anup Patel]

On Wed, Feb 16, 2022 at 5:39 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>
> ---
> Changes from v1->v2:
> 1. Improved the code redability by using arrays instead of individual check
> ---
>  target/riscv/cpu.c | 35 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 34 insertions(+), 1 deletion(-)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index b0a40b83e7a8..9bf8923f164b 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -34,6 +34,13 @@
>
>  /* RISC-V CPU definitions */
>
> +/* This includes the null terminated character '\0' */
> +#define MAX_ISA_EXT_LEN 256
> +struct isa_ext_data {
> +        const char *name;
> +        bool enabled;
> +};
> +
>  static const char riscv_exts[26] = "IEMAFDQCLBJTPVNSUHKORWXYZG";
>
>  const char * const riscv_int_regnames[] = {
> @@ -881,10 +888,35 @@ 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)
> +{
> +    int offset = strnlen(isa_str, max_str_len);
> +    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) {
> +            continue;
> +        }
> +        /* check available space */
> +        if ((offset + strlen(isa_edata_arr[i].name) + 1) > max_str_len) {
> +            qemu_log("No space left to append isa extension");
> +            return;
> +        }
> +        offset += snprintf(isa_str + offset, max_str_len, "_%s",
> +                           isa_edata_arr[i].name);

You don't need to use snprintf() and MAX_ISA_EXT_LEN if you
use g_strconcat() for creating new concat strings and freeing
original string using g_free().

Regards,
Anup

> +    }
> +}
> +
>  char *riscv_isa_string(RISCVCPU *cpu)
>  {
>      int i;
> -    const size_t maxlen = sizeof("rv128") + sizeof(riscv_exts) + 1;
> +    const size_t maxlen = sizeof("rv128") + sizeof(riscv_exts) +
> +                          MAX_ISA_EXT_LEN;
>      char *isa_str = g_new(char, maxlen);
>      char *p = isa_str + snprintf(isa_str, maxlen, "rv%d", TARGET_LONG_BITS);
>      for (i = 0; i < sizeof(riscv_exts); i++) {
> @@ -893,6 +925,7 @@ char *riscv_isa_string(RISCVCPU *cpu)
>          }
>      }
>      *p = '\0';
> +    riscv_isa_string_ext(cpu, isa_str, maxlen);
>      return isa_str;
>  }
>
> --
> 2.30.2
>
>