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

["Christian König" <christian.koenig@amd.com>]

On 09.10.25 17:06, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@kernel.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@amd.com>
> Cc: Jun Lei <jun.lei@amd.com>
> Cc: Harry Wentland <harry.wentland@amd.com>
> Cc: Leo Li <sunpeng.li@amd.com>
> Cc: Rodrigo Siqueira <siqueira@igalia.com>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: "Christian König" <christian.koenig@amd.com>
> Cc: amd-gfx@lists.freedesktop.org
> Cc: dri-devel@lists.freedesktop.org
> Signed-off-by: Ard Biesheuvel <ardb@kernel.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@amd.com>, but Harry and Leo need to take a look.

Thanks,
Christian.

> ---
>  drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.h | 8 ++++++++
>  drivers/gpu/drm/amd/display/dc/os_types.h      | 2 --
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.h b/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.h
> index b8275b397920..4e921632bc4e 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.h
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/dc_fpu.h
> @@ -31,4 +31,12 @@ void dc_assert_fp_enabled(void);
>  void dc_fpu_begin(const char *function_name, const int line);
>  void dc_fpu_end(const char *function_name, const int line);
>  
> +#ifndef _LINUX_FPU_COMPILATION_UNIT
> +#define DC_FP_START()	dc_fpu_begin(__func__, __LINE__)
> +#define DC_FP_END()	dc_fpu_end(__func__, __LINE__)
> +#else
> +#define DC_FP_START()	BUILD_BUG()
> +#define DC_FP_END()	BUILD_BUG()
> +#endif
> +
>  #endif /* __DC_FPU_H__ */
> diff --git a/drivers/gpu/drm/amd/display/dc/os_types.h b/drivers/gpu/drm/amd/display/dc/os_types.h
> index 782316348941..6af831710489 100644
> --- a/drivers/gpu/drm/amd/display/dc/os_types.h
> +++ b/drivers/gpu/drm/amd/display/dc/os_types.h
> @@ -55,8 +55,6 @@
>  
>  #if defined(CONFIG_DRM_AMD_DC_FP)
>  #include "amdgpu_dm/dc_fpu.h"
> -#define DC_FP_START() dc_fpu_begin(__func__, __LINE__)
> -#define DC_FP_END() dc_fpu_end(__func__, __LINE__)
>  #endif /* CONFIG_DRM_AMD_DC_FP */
>  
>  /*