[PATCH v3 4/6] RISC-V: Implement multi-letter ISA extension probing framework

[Atish Patra]

On Tue, Feb 15, 2022 at 2:24 AM Anup Patel <anup at brainfault.org> wrote:
>
> On Tue, Feb 15, 2022 at 2:32 PM Atish Patra <atishp at rivosinc.com> wrote:
> >
> > Multi-letter extensions can be probed using exising
> > riscv_isa_extension_available API now. It doesn't support versioning
> > right now as there is no use case for it.
> > Individual extension specific implementation will be added during
> > each extension support.
> >
> > Signed-off-by: Atish Patra <atishp at rivosinc.com>
> > ---
> >  arch/riscv/include/asm/hwcap.h | 18 ++++++++++++++++++
> >  arch/riscv/kernel/cpufeature.c | 27 ++++++++++++++++++++++++---
> >  2 files changed, 42 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> > index 5ce50468aff1..170bd80da520 100644
> > --- a/arch/riscv/include/asm/hwcap.h
> > +++ b/arch/riscv/include/asm/hwcap.h
> > @@ -34,7 +34,25 @@ extern unsigned long elf_hwcap;
> >  #define RISCV_ISA_EXT_s                ('s' - 'a')
> >  #define RISCV_ISA_EXT_u                ('u' - 'a')
> >
> > +/*
> > + * Increse this to higher value as kernel support more ISA extensions.
> > + */
> >  #define RISCV_ISA_EXT_MAX      64
> > +#define RISCV_ISA_EXT_NAME_LEN_MAX 32
> > +
> > +/* The base ID for multi-letter ISA extensions */
> > +#define RISCV_ISA_EXT_BASE 26
> > +
> > +/*
> > + * This enum represent the logical ID for each multi-letter RISC-V ISA extension.
> > + * The logical ID should start from RISCV_ISA_EXT_BASE and must not exceed
> > + * RISCV_ISA_EXT_MAX. 0-25 range is reserved for single letter
> > + * extensions while all the multi-letter extensions should define the next
> > + * available logical extension id.
> > + */
> > +enum riscv_isa_ext_id {
> > +       RISCV_ISA_EXT_ID_MAX = RISCV_ISA_EXT_MAX,
> > +};
> >
> >  unsigned long riscv_isa_extension_base(const unsigned long *isa_bitmap);
> >
> > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> > index cd9eb34f8d11..af9a57ad3d4e 100644
> > --- a/arch/riscv/kernel/cpufeature.c
> > +++ b/arch/riscv/kernel/cpufeature.c
> > @@ -83,7 +83,7 @@ void __init riscv_fill_hwcap(void)
> >
> >         for_each_of_cpu_node(node) {
> >                 unsigned long this_hwcap = 0;
> > -               unsigned long this_isa = 0;
> > +               uint64_t this_isa = 0;
>
> Why not use a bitmap here ?
>

Yeah. That will simplify things for both RV32 & RV64. Thanks.

> >
> >                 if (riscv_of_processor_hartid(node) < 0)
> >                         continue;
> > @@ -167,12 +167,22 @@ void __init riscv_fill_hwcap(void)
> >                         if (*isa != '_')
> >                                 --isa;
> >
> > +#define SET_ISA_EXT_MAP(name, bit)                                             \
>
> Where is this macro used ?

It will be used in the future where individual extension support will use it.
Here is an example from my debug patch

https://github.com/atishp04/linux/commit/e9e240c9a854dceb434ceb53bdbe82a657bee5f2

>
> > +                       do {                                                    \
> > +                               if ((ext_end - ext == sizeof(name) - 1) &&      \
> > +                                    !memcmp(ext, name, sizeof(name) - 1)) {    \
> > +                                       this_isa |= (1UL << bit);               \
>
> You can use set_bit() here when using bitmap.
>
> > +                                       pr_info("Found ISA extension %s", name);\
> > +                               }                                               \
> > +                       } while (false)                                         \
> > +
> >                         if (unlikely(ext_err))
> >                                 continue;
> >                         if (!ext_long) {
> >                                 this_hwcap |= isa2hwcap[(unsigned char)(*ext)];
> >                                 this_isa |= (1UL << (*ext - 'a'));
> >                         }
> > +#undef SET_ISA_EXT_MAP
> >                 }
> >
> >                 /*
> > @@ -185,10 +195,21 @@ void __init riscv_fill_hwcap(void)
> >                 else
> >                         elf_hwcap = this_hwcap;
> >
> > -               if (riscv_isa[0])
> > +               if (riscv_isa[0]) {
>
> You can use bitmap_weight() here
>
> > +#if IS_ENABLED(CONFIG_32BIT)
> > +                       riscv_isa[0] &= this_isa & 0xFFFFFFFF;
> > +                       riscv_isa[1] &= this_isa >> 32;
> > +#else
> >                         riscv_isa[0] &= this_isa;
> > -               else
> > +#endif
> > +               } else {
> > +#if IS_ENABLED(CONFIG_32BIT)
> > +                       riscv_isa[0] = this_isa & 0xFFFFFFFF;
> > +                       riscv_isa[1] = this_isa >> 32;
> > +#else
> >                         riscv_isa[0] = this_isa;
> > +#endif
> > +               }
> >         }
> >
> >         /* We don't support systems with F but without D, so mask those out
> > --
> > 2.30.2
> >
>
> Regards,
> Anup



-- 
Regards,
Atish