linux-kernel - Re: [PATCH] drm/amd: Permit DC_FP_START/END only in non-FP compilation units

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Message-ID: <CAMj1kXGLdNDJRgQg2Hr9YM4Ke6Sb6KLr8Ws-QY+umR4NpXjg4w@mail.gmail.com>
Date: Thu, 9 Oct 2025 14:27:27 -0700
From: Ard Biesheuvel <ardb@...nel.org>
To: Harry Wentland <harry.wentland@....com>
Cc: Christian König <christian.koenig@....com>, 
	Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, Austin Zheng <austin.zheng@....com>, 
	Jun Lei <jun.lei@....com>, Leo Li <sunpeng.li@....com>, 
	Rodrigo Siqueira <siqueira@...lia.com>, Alex Deucher <alexander.deucher@....com>, 
	amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm/amd: Permit DC_FP_START/END only in non-FP
 compilation units

On Thu, 9 Oct 2025 at 13:41, Harry Wentland <harry.wentland@....com> wrote:
>
>
>
> On 2025-10-09 12:19, Christian König wrote:
> > On 09.10.25 17:06, Ard Biesheuvel wrote:
> >> From: Ard Biesheuvel <ardb@...nel.org>
> >>
> >> Test the existing CPP macro _LINUX_FPU_COMPILATION_UNIT, which is set
> >> when building source files that are permitted to use floating point,
> >> in the implementation of DC_FP_START/END so that those are only usable
> >> in non-FP code. This is a requirement of the generic kernel mode FPU
> >> API, as some architectures (i.e., arm64) cannot safely enable FP codegen
> >> in arbitrary code.
> >
> > If I'm not completely mistaken that is actually an issue on basically all architectures, at least x86 is affected as well if I'm not completely mistaken.
> >
> >> Cc: Austin Zheng <austin.zheng@....com>
> >> Cc: Jun Lei <jun.lei@....com>
> >> Cc: Harry Wentland <harry.wentland@....com>
> >> Cc: Leo Li <sunpeng.li@....com>
> >> Cc: Rodrigo Siqueira <siqueira@...lia.com>
> >> Cc: Alex Deucher <alexander.deucher@....com>
> >> Cc: "Christian König" <christian.koenig@....com>
> >> Cc: amd-gfx@...ts.freedesktop.org
> >> Cc: dri-devel@...ts.freedesktop.org
> >> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> >
> > Anyway, patch looks sane to me but I'm not so deep in the DC code to fully judge.
> >
> > Fell free to add Acked-by: Christian König <christian.koenig@....com>, but Harry and Leo need to take a look.
> >
>
> Thanks. Good safe-guard. Flags a bunch of issues in the
> current code. Let me fix them before merging it.
>
> Reviewed-by: Harry Wentland <harry.wentland@....com>
>

Thanks.

I already fixed a bunch here:
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=ddbfac152830e38d488ff8e45ab7eaf5d72f8527