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

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Message-ID: <87le5kofhj.fsf@linaro.org>
Date: Wed, 10 Apr 2024 22:27:52 -0300
From: Thiago Jung Bauermann <thiago.bauermann@...aro.org>
To: Samuel Holland <samuel.holland@...ive.com>
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


Hello Samuel,

Samuel Holland <samuel.holland@...ive.com> writes:

> 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.

Ok, thank you for clarifying.

Andrew Pinski just responded on the GCC bugzilla and if I understood his
point correctly, it seems to be a matter of changing function names to
what GCC (or actually the arm EABI) expects...

--
Thiago