Re: [PATCH v2 3/4] riscv: replace has_fpu() with system_supports_fpu()

[Anup Patel <anup@brainfault.org>]

On Sun, May 8, 2022 at 9:46 PM Jisheng Zhang <jszhang@kernel.org> wrote:
>
> This is to use the unified cpus_have_{final|const}_cap() instead of
> putting static key related here and there.
>
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> ---
>  arch/riscv/include/asm/cpufeature.h | 5 +++++
>  arch/riscv/include/asm/switch_to.h  | 9 ++-------
>  arch/riscv/kernel/cpufeature.c      | 8 ++------
>  arch/riscv/kernel/process.c         | 2 +-
>  arch/riscv/kernel/signal.c          | 4 ++--
>  5 files changed, 12 insertions(+), 16 deletions(-)
>
> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
> index d80ddd2f3b49..634a653c7fa2 100644
> --- a/arch/riscv/include/asm/cpufeature.h
> +++ b/arch/riscv/include/asm/cpufeature.h
> @@ -91,4 +91,9 @@ static inline void cpus_set_cap(unsigned int num)
>         }
>  }
>
> +static inline bool system_supports_fpu(void)
> +{
> +       return IS_ENABLED(CONFIG_FPU) && !cpus_have_final_cap(RISCV_HAS_NO_FPU);

This should be checking for "f" and "d" ISA extensions since "FPU" is
not an ISA extension name.

> +}
> +
>  #endif
> diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
> index 0a3f4f95c555..362cb18d12d5 100644
> --- a/arch/riscv/include/asm/switch_to.h
> +++ b/arch/riscv/include/asm/switch_to.h
> @@ -8,6 +8,7 @@
>
>  #include <linux/jump_label.h>
>  #include <linux/sched/task_stack.h>
> +#include <asm/cpufeature.h>
>  #include <asm/processor.h>
>  #include <asm/ptrace.h>
>  #include <asm/csr.h>
> @@ -56,13 +57,7 @@ static inline void __switch_to_aux(struct task_struct *prev,
>         fstate_restore(next, task_pt_regs(next));
>  }
>
> -extern struct static_key_false cpu_hwcap_fpu;
> -static __always_inline bool has_fpu(void)
> -{
> -       return static_branch_likely(&cpu_hwcap_fpu);
> -}
>  #else
> -static __always_inline bool has_fpu(void) { return false; }
>  #define fstate_save(task, regs) do { } while (0)
>  #define fstate_restore(task, regs) do { } while (0)
>  #define __switch_to_aux(__prev, __next) do { } while (0)
> @@ -75,7 +70,7 @@ extern struct task_struct *__switch_to(struct task_struct *,
>  do {                                                   \
>         struct task_struct *__prev = (prev);            \
>         struct task_struct *__next = (next);            \
> -       if (has_fpu())                                  \
> +       if (system_supports_fpu())                                      \
>                 __switch_to_aux(__prev, __next);        \
>         ((last) = __switch_to(__prev, __next));         \
>  } while (0)
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index e6c72cad0c1c..1edf3c3f8f62 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -22,10 +22,6 @@ unsigned long elf_hwcap __read_mostly;
>  /* Host ISA bitmap */
>  static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
>
> -#ifdef CONFIG_FPU
> -__ro_after_init DEFINE_STATIC_KEY_FALSE(cpu_hwcap_fpu);
> -#endif
> -
>  DECLARE_BITMAP(cpu_hwcaps, RISCV_NCAPS);
>  EXPORT_SYMBOL(cpu_hwcaps);
>
> @@ -254,8 +250,8 @@ void __init riscv_fill_hwcap(void)
>         pr_info("riscv: ELF capabilities %s\n", print_str);
>
>  #ifdef CONFIG_FPU
> -       if (elf_hwcap & (COMPAT_HWCAP_ISA_F | COMPAT_HWCAP_ISA_D))
> -               static_branch_enable(&cpu_hwcap_fpu);
> +       if (!(elf_hwcap & (COMPAT_HWCAP_ISA_F | COMPAT_HWCAP_ISA_D)))
> +               cpus_set_cap(RISCV_HAS_NO_FPU);
>  #endif
>         enable_cpu_capabilities();
>         static_branch_enable(&riscv_const_caps_ready);
> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> index 504b496787aa..c9cd0b42299e 100644
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -88,7 +88,7 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
>         unsigned long sp)
>  {
>         regs->status = SR_PIE;
> -       if (has_fpu()) {
> +       if (system_supports_fpu()) {
>                 regs->status |= SR_FS_INITIAL;
>                 /*
>                  * Restore the initial value to the FP register
> diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
> index 9f4e59f80551..96aa593a989e 100644
> --- a/arch/riscv/kernel/signal.c
> +++ b/arch/riscv/kernel/signal.c
> @@ -90,7 +90,7 @@ static long restore_sigcontext(struct pt_regs *regs,
>         /* sc_regs is structured the same as the start of pt_regs */
>         err = __copy_from_user(regs, &sc->sc_regs, sizeof(sc->sc_regs));
>         /* Restore the floating-point state. */
> -       if (has_fpu())
> +       if (system_supports_fpu())
>                 err |= restore_fp_state(regs, &sc->sc_fpregs);
>         return err;
>  }
> @@ -143,7 +143,7 @@ static long setup_sigcontext(struct rt_sigframe __user *frame,
>         /* sc_regs is structured the same as the start of pt_regs */
>         err = __copy_to_user(&sc->sc_regs, regs, sizeof(sc->sc_regs));
>         /* Save the floating-point state. */
> -       if (has_fpu())
> +       if (system_supports_fpu())
>                 err |= save_fp_state(regs, &sc->sc_fpregs);
>         return err;
>  }
> --
> 2.34.1
>
>
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Regards,
Anup