linux-kernel - Re: [PATCH 1/2] MIPS: Loongson64: Clean up use of cc-ifversion

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Message-ID: <CAKwvOd=4QBW5uFLM7zbHfG+5499tT_zqBTaZQgzqegmuq_5+MQ@mail.gmail.com>
Date:   Mon, 24 Jan 2022 12:31:31 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc:     Huacai Chen <chenhuacai@...nel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH 1/2] MIPS: Loongson64: Clean up use of cc-ifversion

On Thu, Jan 20, 2022 at 1:40 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> This Makefile checks that GCC is 4.9 or newer, which is redundant after
> commit 76ae847497bc ("Documentation: raise minimum supported version of
> GCC to 5.1"), so cc-option can be removed.
>
> Clang does not support -march=loongson3a so it needs to continue to use
> -march=mips64r2, along with binutils less than 2.25, so check that both
> GCC and binutils 2.25 or newer are being used before using
> -march=loongson3a. These flags do not need to be checked with cc-option
> anymore because all GCC versions support -march=loongson3a and
> -march=mips64r2 and all clang versions support -march=mips64r2.
>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

Thanks for the patch. I wonder why `_MIPS_ISA` only seems to be set at
all for `-march=loongson3a` AFAICT, though that question is orthogonal
to this patch. Perhaps the Loongson or MIPS maintainers know more?
Otherwise seems like most uses of _MIPS_ISA can either be deleted or
simplified now.

Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>  arch/mips/loongson64/Platform | 13 +++----------
>  1 file changed, 3 insertions(+), 10 deletions(-)
>
> diff --git a/arch/mips/loongson64/Platform b/arch/mips/loongson64/Platform
> index 3e660d6d3c2b..981d3abc150e 100644
> --- a/arch/mips/loongson64/Platform
> +++ b/arch/mips/loongson64/Platform
> @@ -12,17 +12,10 @@ cflags-$(CONFIG_CPU_LOONGSON64)     += -Wa,--trap
>  # by GAS.  The cc-option can't probe for this behaviour so -march=loongson3a
>  # can't easily be used safely within the kbuild framework.
>  #
> -ifeq ($(call cc-ifversion, -ge, 0409, y), y)
> -  ifeq ($(call ld-ifversion, -ge, 22500, y), y)
> -    cflags-$(CONFIG_CPU_LOONGSON64)  += \
> -      $(call cc-option,-march=loongson3a -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS64)
> -  else
> -    cflags-$(CONFIG_CPU_LOONGSON64)  += \
> -      $(call cc-option,-march=mips64r2,-mips64r2 -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS64)
> -  endif
> +ifeq ($(CONFIG_CC_IS_GCC)$(call ld-ifversion, -ge, 22500, y), yy)
> +  cflags-$(CONFIG_CPU_LOONGSON64) += -march=loongson3a -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS64
>  else
> -    cflags-$(CONFIG_CPU_LOONGSON64)  += \
> -      $(call cc-option,-march=mips64r2,-mips64r2 -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS64)
> +  cflags-$(CONFIG_CPU_LOONGSON64) += -march=mips64r2
>  endif
>
>  # Some -march= flags enable MMI instructions, and GCC complains about that
>
> base-commit: 2c271fe77d52a0555161926c232cd5bc07178b39
> --
> 2.34.1
>


-- 
Thanks,
~Nick Desaulniers