linux-kernel - Re: [PATCH] ARM: Do not select ARCH_HAS_KERNEL_FPU

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Message-ID: <CAMj1kXFfWKh-oM8q11eEF94mPOENHxW+fdvkYLSbUDs0ZG8Sow@mail.gmail.com>
Date: Thu, 9 May 2024 09:39:59 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Samuel Holland <samuel.holland@...ive.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, 
	Thiago Jung Bauermann <thiago.bauermann@...aro.org>, kernel test robot <lkp@...el.com>, Andrew Davis <afd@...com>, 
	Arnd Bergmann <arnd@...db.de>, Christian König <christian.koenig@....com>, 
	Eric DeVolder <eric.devolder@...cle.com>, Rob Herring <robh@...nel.org>, 
	Russell King <linux@...linux.org.uk>, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] ARM: Do not select ARCH_HAS_KERNEL_FPU_SUPPORT

On Thu, 9 May 2024 at 03:37, Samuel Holland <samuel.holland@...ive.com> wrote:
>
> On 32-bit ARM, conversions between `double` and `long long` require
> runtime library support. Since the kernel does not currently provide
> this library support, the amdgpu driver fails to build:
>
>   ERROR: modpost: "__aeabi_l2d" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!
>   ERROR: modpost: "__aeabi_d2ulz" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!
>
> As Arnd reports, there are likely no 32-bit ARM platforms which can use
> the amdgpu driver anyway, due to lack of features like 64-bit
> prefetchable BARs. Since amdgpu is currently the only real user of
> ARCH_HAS_KERNEL_FPU_SUPPORT, drop support for this option instead of
> bothering to implement the library functions.
>
> Fixes: 12624fe2d707 ("ARM: implement ARCH_HAS_KERNEL_FPU_SUPPORT")

This commit is not in mainline yet. Could we just drop the original
patch instead?

> Reported-by: Thiago Jung Bauermann <thiago.bauermann@...aro.org>
> Closes: https://lore.kernel.org/lkml/87wmp4oo3y.fsf@linaro.org/
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202404042327.jRpt81kP-lkp@intel.com/
> Suggested-by: Ard Biesheuvel <ardb@...nel.org>
> Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
> ---
>
>  arch/arm/Kconfig | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index b1751c2cab87..b14aed3a17ab 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -15,7 +15,6 @@ config ARM
>         select ARCH_HAS_FORTIFY_SOURCE
>         select ARCH_HAS_KEEPINITRD
>         select ARCH_HAS_KCOV
> -       select ARCH_HAS_KERNEL_FPU_SUPPORT if KERNEL_MODE_NEON
>         select ARCH_HAS_MEMBARRIER_SYNC_CORE
>         select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
>         select ARCH_HAS_PTE_SPECIAL if ARM_LPAE
> --
> 2.44.0
>