[PATCH v5 2/6] RISC-V: Minimal parser for "riscv, isa" strings

[Anup Patel]

On Wed, Feb 23, 2022 at 2:18 AM Atish Patra <atishp at rivosinc.com> wrote:
>
> From: Tsukasa OI <research_trasio at irq.a4lg.com>
>
> Current hart ISA ("riscv,isa") parser don't correctly parse:
>
> 1. Multi-letter extensions
> 2. Version numbers
>
> All ISA extensions ratified recently has multi-letter extensions
> (except 'H'). The current "riscv,isa" parser that is easily confused
> by multi-letter extensions and "p" in version numbers can be a huge
> problem for adding new extensions through the device tree.
>
> Leaving it would create incompatible hacks and would make "riscv,isa"
> value unreliable.
>
> This commit implements minimal parser for "riscv,isa" strings.  With this,
> we can safely ignore multi-letter extensions and version numbers.
>
> [Improved commit text and fixed a bug around 's' in base extension]
> Signed-off-by: Atish Patra <atishp at rivosinc.com>
> [Fixed workaround for QEMU]
> Signed-off-by: Tsukasa OI <research_trasio at irq.a4lg.com>
> Tested-by: Heiko Stuebner <heiko at sntech.de>

Looks good to me.

Reviewed-by: Anup Patel <anup at brainfault.org>

Regards,
Anup

> ---
>  arch/riscv/kernel/cpufeature.c | 72 ++++++++++++++++++++++++++++------
>  1 file changed, 61 insertions(+), 11 deletions(-)
>
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index dd3d57eb4eea..72c5f6ef56b5 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -7,6 +7,7 @@
>   */
>
>  #include <linux/bitmap.h>
> +#include <linux/ctype.h>
>  #include <linux/of.h>
>  #include <asm/processor.h>
>  #include <asm/hwcap.h>
> @@ -66,7 +67,7 @@ void __init riscv_fill_hwcap(void)
>         struct device_node *node;
>         const char *isa;
>         char print_str[NUM_ALPHA_EXTS + 1];
> -       size_t i, j, isa_len;
> +       int i, j;
>         static unsigned long isa2hwcap[256] = {0};
>
>         isa2hwcap['i'] = isa2hwcap['I'] = COMPAT_HWCAP_ISA_I;
> @@ -92,23 +93,72 @@ void __init riscv_fill_hwcap(void)
>                         continue;
>                 }
>
> -               i = 0;
> -               isa_len = strlen(isa);
>  #if IS_ENABLED(CONFIG_32BIT)
>                 if (!strncmp(isa, "rv32", 4))
> -                       i += 4;
> +                       isa += 4;
>  #elif IS_ENABLED(CONFIG_64BIT)
>                 if (!strncmp(isa, "rv64", 4))
> -                       i += 4;
> +                       isa += 4;
>  #endif
> -               for (; i < isa_len; ++i) {
> -                       this_hwcap |= isa2hwcap[(unsigned char)(isa[i])];
> +               for (; *isa; ++isa) {
> +                       const char *ext = isa++;
> +                       const char *ext_end = isa;
> +                       bool ext_long = false, ext_err = false;
> +
> +                       switch (*ext) {
> +                       case 's':
> +                               /**
> +                                * Workaround for invalid single-letter 's' & 'u'(QEMU).
> +                                * No need to set the bit in riscv_isa as 's' & 'u' are
> +                                * not valid ISA extensions. It works until multi-letter
> +                                * extension starting with "Su" appears.
> +                                */
> +                               if (ext[-1] != '_' && ext[1] == 'u') {
> +                                       ++isa;
> +                                       ext_err = true;
> +                                       break;
> +                               }
> +                               fallthrough;
> +                       case 'x':
> +                       case 'z':
> +                               ext_long = true;
> +                               /* Multi-letter extension must be delimited */
> +                               for (; *isa && *isa != '_'; ++isa)
> +                                       if (!islower(*isa) && !isdigit(*isa))
> +                                               ext_err = true;
> +                               break;
> +                       default:
> +                               if (unlikely(!islower(*ext))) {
> +                                       ext_err = true;
> +                                       break;
> +                               }
> +                               /* Find next extension */
> +                               if (!isdigit(*isa))
> +                                       break;
> +                               /* Skip the minor version */
> +                               while (isdigit(*++isa))
> +                                       ;
> +                               if (*isa != 'p')
> +                                       break;
> +                               if (!isdigit(*++isa)) {
> +                                       --isa;
> +                                       break;
> +                               }
> +                               /* Skip the major version */
> +                               while (isdigit(*++isa))
> +                                       ;
> +                               break;
> +                       }
> +                       if (*isa != '_')
> +                               --isa;
>                         /*
> -                        * TODO: X, Y and Z extension parsing for Host ISA
> -                        * bitmap will be added in-future.
> +                        * TODO: Full version-aware handling including
> +                        * multi-letter extensions will be added in-future.
>                          */
> -                       if ('a' <= isa[i] && isa[i] < 'x')
> -                               this_isa |= (1UL << (isa[i] - 'a'));
> +                       if (ext_err || ext_long)
> +                               continue;
> +                       this_hwcap |= isa2hwcap[(unsigned char)(*ext)];
> +                       this_isa |= (1UL << (*ext - 'a'));
>                 }
>
>                 /*
> --
> 2.30.2
>