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Date:   Tue, 25 Jan 2022 00:03:32 +0000
From:   "Jiaxun Yang" <jiaxun.yang@flygoat.com>
To:     "Nick Desaulniers" <ndesaulniers@google.com>,
        "Nathan Chancellor" <nathan@kernel.org>,
        "Thomas Bogendoerfer" <tsbogend@alpha.franken.de>
Cc:     "Huacai Chen" <chenhuacai@kernel.org>,
        "linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
        linux-kernel@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [PATCH 1/2] MIPS: Loongson64: Clean up use of cc-ifversion
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=E5=9C=A82022=E5=B9=B41=E6=9C=8824=E6=97=A5=E4=B8=80=E6=9C=88 =E4=B8=8B=E5=
=8D=888:31=EF=BC=8CNick Desaulniers=E5=86=99=E9=81=93=EF=BC=9A
> On Thu, Jan 20, 2022 at 1:40 PM Nathan Chancellor <nathan@kernel.org> =
wrote:
>>
>> This Makefile checks that GCC is 4.9 or newer, which is redundant aft=
er
>> commit 76ae847497bc ("Documentation: raise minimum supported version =
of
>> GCC to 5.1"), so cc-option can be removed.
>>
>> Clang does not support -march=3Dloongson3a so it needs to continue to=
 use
>> -march=3Dmips64r2, along with binutils less than 2.25, so check that =
both
>> GCC and binutils 2.25 or newer are being used before using
>> -march=3Dloongson3a. These flags do not need to be checked with cc-op=
tion
>> anymore because all GCC versions support -march=3Dloongson3a and
>> -march=3Dmips64r2 and all clang versions support -march=3Dmips64r2.
>>
>> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
>
> Thanks for the patch. I wonder why `_MIPS_ISA` only seems to be set at
> all for `-march=3Dloongson3a` AFAICT, though that question is orthogon=
al
> 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.

This is because earlier GCC mistakenly set loongson3a to MIPS64 not MIPS=
64R2.

But given that it's earlier than the minimal requirement GCC of kernel t=
oday, I think it should be safe to just move the whole logic.

Thanks.

>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
>
>> ---
>>  arch/mips/loongson64/Platform | 13 +++----------
>>  1 file changed, 3 insertions(+), 10 deletions(-)
>>
>> diff --git a/arch/mips/loongson64/Platform b/arch/mips/loongson64/Pla=
tform
>> index 3e660d6d3c2b..981d3abc150e 100644
>> --- a/arch/mips/loongson64/Platform
>> +++ b/arch/mips/loongson64/Platform
>> @@ -12,17 +12,10 @@ cflags-$(CONFIG_CPU_LOONGSON64)     +=3D -Wa,--tr=
ap
>>  # by GAS.  The cc-option can't probe for this behaviour so -march=3D=
loongson3a
>>  # can't easily be used safely within the kbuild framework.
>>  #
>> -ifeq ($(call cc-ifversion, -ge, 0409, y), y)
>> -  ifeq ($(call ld-ifversion, -ge, 22500, y), y)
>> -    cflags-$(CONFIG_CPU_LOONGSON64)  +=3D \
>> -      $(call cc-option,-march=3Dloongson3a -U_MIPS_ISA -D_MIPS_ISA=3D=
_MIPS_ISA_MIPS64)
>> -  else
>> -    cflags-$(CONFIG_CPU_LOONGSON64)  +=3D \
>> -      $(call cc-option,-march=3Dmips64r2,-mips64r2 -U_MIPS_ISA -D_MI=
PS_ISA=3D_MIPS_ISA_MIPS64)
>> -  endif
>> +ifeq ($(CONFIG_CC_IS_GCC)$(call ld-ifversion, -ge, 22500, y), yy)
>> +  cflags-$(CONFIG_CPU_LOONGSON64) +=3D -march=3Dloongson3a -U_MIPS_I=
SA -D_MIPS_ISA=3D_MIPS_ISA_MIPS64
>>  else
>> -    cflags-$(CONFIG_CPU_LOONGSON64)  +=3D \
>> -      $(call cc-option,-march=3Dmips64r2,-mips64r2 -U_MIPS_ISA -D_MI=
PS_ISA=3D_MIPS_ISA_MIPS64)
>> +  cflags-$(CONFIG_CPU_LOONGSON64) +=3D -march=3Dmips64r2
>>  endif
>>
>>  # Some -march=3D flags enable MMI instructions, and GCC complains ab=
out that
>>
>> base-commit: 2c271fe77d52a0555161926c232cd5bc07178b39
>> --
>> 2.34.1
>>
>
>
> --=20
> Thanks,
> ~Nick Desaulniers

--=20
- Jiaxun