Re: [PATCH v5] target/riscv: Add isa extenstion strings to the device tree

[Bin Meng <bmeng.cn@gmail.com>]

On Tue, Mar 15, 2022 at 7:43 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

nits: remove one space after "appending"

> to the "riscv,isa" string if it is enabled so that kernel can process it.
>
> [1] https://lkml.org/lkml/2022/2/15/263

Could you please post a link to the "riscv,isa" DT bindings spec or
discussion thread? It seems not mentioned in the above LKML thread.

>
> Reviewed-by: Anup Patel <anup@brainfault.org>
> Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
> Suggested-by: Heiko Stubner <heiko@sntech.de>
> Signed-off-by: Atish Patra <atishp@rivosinc.com>
> ---
> Changes from v4->v5:
> 1. Fixed the order of Zxx extensions.
> 2. Added a comment clearly describing the rules of extension order.
>
> Changes from v3->v4:
> 1. Fixed the order of the extension names.
> 2. Added all the available ISA extensions in Qemu.
>
> 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 | 61 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 61 insertions(+)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index ddda4906ffb7..097c42f5c50f 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[] = {
> @@ -898,6 +904,60 @@ static void riscv_cpu_class_init(ObjectClass *c, void *data)
>      device_class_set_props(dc, riscv_cpu_properties);
>  }
>
> +#define ISA_EDATA_ENTRY(name, prop) {#name, cpu->cfg.prop}
> +
> +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;
> +
> +    /**
> +     * Here are the ordering rules of extension naming defined by RISC-V
> +     * specification :
> +     * 1. All extensions should be separated from other multi-letter extensions
> +     *    from other multi-letter extensions by an underscore.

redundant "from other multi-letter extensions"

> +     * 2. The first letter following the 'Z' conventionally indicates the most

Should this be lower case "z"?

> +     *    closely related alphabetical extension category, IMAFDQLCBKJTPVH.
> +     *    If multiple 'Z' extensions are named, they should be ordered first
> +     *    by category, then alphabetically within a category.
> +     * 3. Standard supervisor-level extensions (starts with 'S') should be

lower case "s"?

> +     *    listed after standard unprivileged extensions.  If multiple
> +     *    supervisor-level extensions are listed, they should be ordered
> +     *    alphabetically.
> +     * 4. Non-standard extensions (starts with 'X') must be listed after all
> +     *    standard extensions. They must be separated from other multi-letter
> +     *    extensions by an underscore.
> +     */
> +    struct isa_ext_data isa_edata_arr[] = {
> +        ISA_EDATA_ENTRY(zfh, ext_zfhmin),

This should be (zfh, ext_zfh)

> +        ISA_EDATA_ENTRY(zfhmin, ext_zfhmin),
> +        ISA_EDATA_ENTRY(zfinx, ext_zfinx),
> +        ISA_EDATA_ENTRY(zdinx, ext_zdinx),

Should "zdinx" come before "zfinx" *alphabetically* ?

> +        ISA_EDATA_ENTRY(zba, ext_zba),
> +        ISA_EDATA_ENTRY(zbb, ext_zbb),
> +        ISA_EDATA_ENTRY(zbc, ext_zbc),
> +        ISA_EDATA_ENTRY(zbs, ext_zbs),

I don't understand why "zb*" come after "zf*". Alphabetically they
should come before.

> +        ISA_EDATA_ENTRY(zve32f, ext_zve32f),
> +        ISA_EDATA_ENTRY(zve64f, ext_zve64f),
> +        ISA_EDATA_ENTRY(zhinx, ext_zhinx),
> +        ISA_EDATA_ENTRY(zhinxmin, ext_zhinxmin),
> +        ISA_EDATA_ENTRY(svinval, ext_svinval),
> +        ISA_EDATA_ENTRY(svnapot, ext_svnapot),
> +        ISA_EDATA_ENTRY(svpbmt, ext_svpbmt),
> +    };
> +
> +    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;
> @@ -910,6 +970,7 @@ char *riscv_isa_string(RISCVCPU *cpu)
>          }
>      }
>      *p = '\0';
> +    riscv_isa_string_ext(cpu, &isa_str, maxlen);
>      return isa_str;
>  }
>

Regards,
Bin