linux-kernel - [PATCH] drm/amd/display/dml2: Guard dml21_map_dc_state_into_dml_display_cfg with DC_FP

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Message-ID: <20250825085211.34396-1-xry111@xry111.site>
Date: Mon, 25 Aug 2025 16:52:11 +0800
From: Xi Ruoyao <xry111@...111.site>
To: Alex Deucher <alexander.deucher@....com>,
	Christian König <christian.koenig@....com>
Cc: amd-gfx@...ts.freedesktop.org,
	Huacai Chen <chenhuacai@...nel.org>,
	WANG Xuerui <kernel@...0n.name>,
	Mingcong Bai <jeffbai@...c.io>,
	dri-devel@...ts.freedesktop.org,
	loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Xi Ruoyao <xry111@...111.site>,
	Asiacn <710187964@...com>
Subject: [PATCH] drm/amd/display/dml2: Guard dml21_map_dc_state_into_dml_display_cfg with DC_FP_START

dml21_map_dc_state_into_dml_display_cfg calls (the call is usually
inlined by the compiler) populate_dml21_surface_config_from_plane_state
and populate_dml21_plane_config_from_plane_state which may use FPU.  In
a x86-64 build:

    $ objdump --disassemble=dml21_map_dc_state_into_dml_display_cfg \
    > drivers/gpu/drm/amd/display/dc/dml2/dml21/dml21_translation_helper.o |
    > grep %xmm -c
    63

Thus it needs to be guarded with DC_FP_START.  But we must note that the
current code quality of the in-kernel FPU use in AMD dml2 is very much
problematic: we are actually calling DC_FP_START in dml21_wrapper.c
here, and this translation unit is built with CC_FLAGS_FPU.  Strictly
speaking this does not make any sense: with CC_FLAGS_FPU the compiler is
allowed to generate FPU uses anywhere in the translated code, perhaps
out of the DC_FP_START guard.  This problematic pattern also occurs in
at least dml2_wrapper.c, dcn35_fpu.c, and dcn351_fpu.c.  Thus we really
need a careful audit and refactor for the in-kernel FPU uses, and this
patch is simply whacking a mole.  However per the reporter, whacking
this mole is enough to make a 9060XT "just work."

Reported-by: Asiacn <710187964@...com>
Link: https://github.com/loongson-community/discussions/issues/102
Tested-by: Asiacn <710187964@...com>
Signed-off-by: Xi Ruoyao <xry111@...111.site>
---
 drivers/gpu/drm/amd/display/dc/dml2/dml21/dml21_wrapper.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/dc/dml2/dml21/dml21_wrapper.c b/drivers/gpu/drm/amd/display/dc/dml2/dml21/dml21_wrapper.c
index 03de3cf06ae5..059ede6ff256 100644
--- a/drivers/gpu/drm/amd/display/dc/dml2/dml21/dml21_wrapper.c
+++ b/drivers/gpu/drm/amd/display/dc/dml2/dml21/dml21_wrapper.c
@@ -224,7 +224,9 @@ static bool dml21_mode_check_and_programming(const struct dc *in_dc, struct dc_s
 	dml_ctx->config.svp_pstate.callbacks.release_phantom_streams_and_planes(in_dc, context);
 
 	/* Populate stream, plane mappings and other fields in display config. */
+	DC_FP_START();
 	result = dml21_map_dc_state_into_dml_display_cfg(in_dc, context, dml_ctx);
+	DC_FP_END();
 	if (!result)
 		return false;
 
@@ -279,7 +281,9 @@ static bool dml21_check_mode_support(const struct dc *in_dc, struct dc_state *co
 	dml_ctx->config.svp_pstate.callbacks.release_phantom_streams_and_planes(in_dc, context);
 
 	mode_support->dml2_instance = dml_init->dml2_instance;
+	DC_FP_START();
 	dml21_map_dc_state_into_dml_display_cfg(in_dc, context, dml_ctx);
+	DC_FP_END();
 	dml_ctx->v21.mode_programming.dml2_instance->scratch.build_mode_programming_locals.mode_programming_params.programming = dml_ctx->v21.mode_programming.programming;
 	DC_FP_START();
 	is_supported = dml2_check_mode_supported(mode_support);
-- 
2.51.0