linux-kernel - Re: [PATCH v2 2/2] riscv: Disable misaligned access probe when CONFIG_HAVE_EFFICIENT_UNALIGNED

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Date: Fri, 2 Feb 2024 15:01:01 -0800
From: Eric Biggers <ebiggers@...nel.org>
To: Charlie Jenkins <charlie@...osinc.com>
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Jisheng Zhang <jszhang@...nel.org>, Evan Green <evan@...osinc.com>,
	Clément Léger <cleger@...osinc.com>,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] riscv: Disable misaligned access probe when
 CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS

On Thu, Feb 01, 2024 at 03:30:46PM -0800, Charlie Jenkins wrote:
> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
> index eb3ac304fc42..3a29d8e30e05 100644
> --- a/arch/riscv/include/asm/cpufeature.h
> +++ b/arch/riscv/include/asm/cpufeature.h
> @@ -51,6 +51,7 @@ static inline bool check_unaligned_access_emulated(int cpu)
>  static inline void unaligned_emulation_finish(void) {}
>  #endif
>  
> +#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS

#ifdef..#else..#endif is more readable than #ifndef..#else..#endif.

> diff --git a/arch/riscv/include/asm/misaligned_access_speed.h b/arch/riscv/include/asm/misaligned_access_speed.h
> new file mode 100644
> index 000000000000..81df2aa6fa6b
> --- /dev/null
> +++ b/arch/riscv/include/asm/misaligned_access_speed.h

This new header file isn't included from anywhere.

> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index f71910718053..8be7f17da9ab 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -62,6 +62,9 @@ obj-y	+= tests/
>  obj-$(CONFIG_MMU) += vdso.o vdso/
>  
>  obj-$(CONFIG_RISCV_MISALIGNED)	+= traps_misaligned.o
> +ifneq ($(RISCV_EFFICIENT_UNALIGNED_ACCESS), y)
> +obj-y	+= misaligned_access_speed.o
> +endif

CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS

> diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
> index a7c56b41efd2..3f1a6edfdb08 100644
> --- a/arch/riscv/kernel/sys_hwprobe.c
> +++ b/arch/riscv/kernel/sys_hwprobe.c
> @@ -149,6 +149,7 @@ static bool hwprobe_ext0_has(const struct cpumask *cpus, unsigned long ext)
>  
>  static u64 hwprobe_misaligned(const struct cpumask *cpus)
>  {
> +#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
>  	int cpu;
>  	u64 perf = -1ULL;
>  
> @@ -168,6 +169,9 @@ static u64 hwprobe_misaligned(const struct cpumask *cpus)
>  		return RISCV_HWPROBE_MISALIGNED_UNKNOWN;
>  
>  	return perf;
> +#else
> +	return RISCV_HWPROBE_MISALIGNED_FAST;
> +#endif

#ifdef..#else..#endif is more readable than #ifndef..#else..#endif.

- Eric