linux-kernel - Re: [PATCH v2 07/14] LoongArch: Implement ARCH_HAS_KERNEL_FPU

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Date: Thu, 4 Jan 2024 09:58:28 -0600
From: Samuel Holland <samuel.holland@...ive.com>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org,
 x86@...nel.org, linux-riscv@...ts.infradead.org,
 Christoph Hellwig <hch@....de>, loongarch@...ts.linux.dev,
 linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
 linux-arch@...r.kernel.org, WANG Xuerui <git@...0n.name>
Subject: Re: [PATCH v2 07/14] LoongArch: Implement ARCH_HAS_KERNEL_FPU_SUPPORT

Hi Huacai,

On 2024-01-04 3:55 AM, Huacai Chen wrote:
> Hi, Samuel,
> 
> On Thu, Dec 28, 2023 at 9:42 AM Samuel Holland
> <samuel.holland@...ive.com> wrote:
>>
>> LoongArch already provides kernel_fpu_begin() and kernel_fpu_end() in
>> asm/fpu.h, so it only needs to add kernel_fpu_available() and export
>> the CFLAGS adjustments.
>>
>> Acked-by: WANG Xuerui <git@...0n.name>
>> Reviewed-by: Christoph Hellwig <hch@....de>
>> Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
>> ---
>>
>> (no changes since v1)
>>
>>  arch/loongarch/Kconfig           | 1 +
>>  arch/loongarch/Makefile          | 5 ++++-
>>  arch/loongarch/include/asm/fpu.h | 1 +
>>  3 files changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
>> index ee123820a476..65d4475565b8 100644
>> --- a/arch/loongarch/Kconfig
>> +++ b/arch/loongarch/Kconfig
>> @@ -15,6 +15,7 @@ config LOONGARCH
>>         select ARCH_HAS_CPU_FINALIZE_INIT
>>         select ARCH_HAS_FORTIFY_SOURCE
>>         select ARCH_HAS_KCOV
>> +       select ARCH_HAS_KERNEL_FPU_SUPPORT if CPU_HAS_FPU
>>         select ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
>>         select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
>>         select ARCH_HAS_PTE_SPECIAL
>> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
>> index 4ba8d67ddb09..1afe28feaba5 100644
>> --- a/arch/loongarch/Makefile
>> +++ b/arch/loongarch/Makefile
>> @@ -25,6 +25,9 @@ endif
>>  32bit-emul             = elf32loongarch
>>  64bit-emul             = elf64loongarch
>>
>> +CC_FLAGS_FPU           := -mfpu=64
>> +CC_FLAGS_NO_FPU                := -msoft-float
> We will add LoongArch32 support later, maybe it should be -mfpu=32 in
> that case, and do other archs have the case that only support FP32?

Do you mean that LoongArch32 does not support double-precision FP in hardware?
At least both of the consumers in this series use double-precision, so my first
thought is that LoongArch32 could not select ARCH_HAS_KERNEL_FPU_SUPPORT.

Regards,
Samuel