[PATCH] drm/amd/display: readd -msse2 to prevent Clang from emitting libcalls to undefined SW FP routines

[Nick Desaulniers <ndesaulniers@google.com>]

arch/x86/Makefile disables SSE and SSE2 for the whole kernel.  The
AMDGPU drivers modified in this patch re-enable SSE but not SSE2.  Turn
on SSE2 to support emitting double precision floating point instructions
rather than calls to non-existent (usually available from gcc_s or
compiler_rt) floating point helper routines for Clang.

This was originally landed in:
commit 10117450735c ("drm/amd/display: add -msse2 to prevent Clang from emitting libcalls to undefined SW FP routines")
but reverted in:
commit 193392ed9f69 ("Revert "drm/amd/display: add -msse2 to prevent Clang from emitting libcalls to undefined SW FP routines"")
due to bugreports from GCC builds. Add guards to only do so for Clang.

Link: https://bugs.freedesktop.org/show_bug.cgi?id=109487
Link: https://github.com/ClangBuiltLinux/linux/issues/327

Suggested-by: Sedat Dilek <sedat.dilek@gmail.com>
Suggested-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 drivers/gpu/drm/amd/display/dc/calcs/Makefile | 4 ++++
 drivers/gpu/drm/amd/display/dc/dcn20/Makefile | 4 ++++
 drivers/gpu/drm/amd/display/dc/dml/Makefile   | 4 ++++
 drivers/gpu/drm/amd/display/dc/dsc/Makefile   | 4 ++++
 4 files changed, 16 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/dc/calcs/Makefile b/drivers/gpu/drm/amd/display/dc/calcs/Makefile
index 95f332ee3e7e..16614d73a5fc 100644
--- a/drivers/gpu/drm/amd/display/dc/calcs/Makefile
+++ b/drivers/gpu/drm/amd/display/dc/calcs/Makefile
@@ -32,6 +32,10 @@ endif
 
 calcs_ccflags := -mhard-float -msse $(cc_stack_align)
 
+ifdef CONFIG_CC_IS_CLANG
+calcs_ccflags += -msse2
+endif
+
 CFLAGS_dcn_calcs.o := $(calcs_ccflags)
 CFLAGS_dcn_calc_auto.o := $(calcs_ccflags)
 CFLAGS_dcn_calc_math.o := $(calcs_ccflags) -Wno-tautological-compare
diff --git a/drivers/gpu/drm/amd/display/dc/dcn20/Makefile b/drivers/gpu/drm/amd/display/dc/dcn20/Makefile
index e9721a906592..f57a3b281408 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn20/Makefile
+++ b/drivers/gpu/drm/amd/display/dc/dcn20/Makefile
@@ -18,6 +18,10 @@ endif
 
 CFLAGS_dcn20_resource.o := -mhard-float -msse $(cc_stack_align)
 
+ifdef CONFIG_CC_IS_CLANG
+CFLAGS_dcn20_resource.o += -msse2
+endif
+
 AMD_DAL_DCN20 = $(addprefix $(AMDDALPATH)/dc/dcn20/,$(DCN20))
 
 AMD_DISPLAY_FILES += $(AMD_DAL_DCN20)
diff --git a/drivers/gpu/drm/amd/display/dc/dml/Makefile b/drivers/gpu/drm/amd/display/dc/dml/Makefile
index 0bb7a20675c4..132ade1a234e 100644
--- a/drivers/gpu/drm/amd/display/dc/dml/Makefile
+++ b/drivers/gpu/drm/amd/display/dc/dml/Makefile
@@ -32,6 +32,10 @@ endif
 
 dml_ccflags := -mhard-float -msse $(cc_stack_align)
 
+ifdef CONFIG_CC_IS_CLANG
+dml_ccflags += -msse2
+endif
+
 CFLAGS_display_mode_lib.o := $(dml_ccflags)
 
 ifdef CONFIG_DRM_AMD_DC_DCN2_0
diff --git a/drivers/gpu/drm/amd/display/dc/dsc/Makefile b/drivers/gpu/drm/amd/display/dc/dsc/Makefile
index e019cd9447e8..17db603f2d1f 100644
--- a/drivers/gpu/drm/amd/display/dc/dsc/Makefile
+++ b/drivers/gpu/drm/amd/display/dc/dsc/Makefile
@@ -9,6 +9,10 @@ endif
 
 dsc_ccflags := -mhard-float -msse $(cc_stack_align)
 
+ifdef CONFIG_CC_IS_CLANG
+dsc_ccflags += -msse2
+endif
+
 CFLAGS_rc_calc.o := $(dsc_ccflags)
 CFLAGS_rc_calc_dpi.o := $(dsc_ccflags)
 CFLAGS_codec_main_amd.o := $(dsc_ccflags)
-- 
2.22.0.657.g960e92d24f-goog