linux-kernel - Re: [PATCH v4 13/15] drm/amd/display: Use ARCH_HAS_KERNEL_FPU

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Date: Wed, 10 Apr 2024 20:11:04 -0500
From: Samuel Holland <samuel.holland@...ive.com>
To: Thiago Jung Bauermann <thiago.bauermann@...aro.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 linux-arm-kernel@...ts.infradead.org, x86@...nel.org,
 linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
 linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
 Christoph Hellwig <hch@....de>, loongarch@...ts.linux.dev,
 amd-gfx@...ts.freedesktop.org, Alex Deucher <alexander.deucher@....com>
Subject: Re: [PATCH v4 13/15] drm/amd/display: Use ARCH_HAS_KERNEL_FPU_SUPPORT

Hi Thiago,

On 2024-04-10 8:02 PM, Thiago Jung Bauermann wrote:
> Samuel Holland <samuel.holland@...ive.com> writes:
>> On 2024-04-10 5:21 PM, Thiago Jung Bauermann wrote:
>>>
>>> Unfortunately this patch causes build failures on arm with allyesconfig
>>> and allmodconfig. Tested with next-20240410.
> 
> <snip>
> 
>> In both cases, the issue is that the toolchain requires runtime support to
>> convert between `unsigned long long` and `double`, even when hardware FP is
>> enabled. There was some past discussion about GCC inlining some of these
>> conversions[1], but that did not get implemented.
> 
> Thank you for the explanation and the bugzilla reference. I added a
> comment there mentioning that the problem came up again with this patch
> series.
> 
>> The short-term fix would be to drop the `select ARCH_HAS_KERNEL_FPU_SUPPORT` for
>> 32-bit arm until we can provide these runtime library functions.
> 
> Does this mean that patch 2 in this series:
> 
> [PATCH v4 02/15] ARM: Implement ARCH_HAS_KERNEL_FPU_SUPPORT
> 
> will be dropped?

No, because later patches in the series (3, 6) depend on the definition of
CC_FLAGS_FPU from that patch. I will need to send a fixup patch unless I can
find a GPL-2 compatible implementation of the runtime library functions.

Regards,
Samuel