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

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Message-ID: <20251009150621.3886079-2-ardb+git@google.com>
Date: Thu,  9 Oct 2025 17:06:21 +0200
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: linux-arm-kernel@...ts.infradead.org, Ard Biesheuvel <ardb@...nel.org>, 
	Austin Zheng <austin.zheng@....com>, Jun Lei <jun.lei@....com>, 
	Harry Wentland <harry.wentland@....com>, Leo Li <sunpeng.li@....com>, 
	Rodrigo Siqueira <siqueira@...lia.com>, Alex Deucher <alexander.deucher@....com>, 
	"Christian König" <christian.koenig@....com>, amd-gfx@...ts.freedesktop.org, 
	dri-devel@...ts.freedesktop.org
Subject: [PATCH] drm/amd: Permit DC_FP_START/END only in non-FP compilation units

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.

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>
---
 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 */
 
 /*
-- 
2.51.0.710.ga91ca5db03-goog