Re: [PATCH] drm/amd/display: Add missing hard-float compile flags for PPC64 builds

[Guenter Roeck <linux@roeck-us.net>]

On Thu, Jun 30, 2022 at 05:01:01PM -0400, Rodrigo Siqueira Jordao wrote:
> 
> 
> On 2022-06-18 19:27, Guenter Roeck wrote:
> > ppc:allmodconfig builds fail with the following error.
> > 
> > powerpc64-linux-ld:
> > 	drivers/gpu/drm/amd/amdgpu/../display/dc/dml/display_mode_lib.o
> > 		uses hard float,
> > 	drivers/gpu/drm/amd/amdgpu/../display/dc/dcn31/dcn31_resource.o
> > 		uses soft float
> > powerpc64-linux-ld:
> > 	failed to merge target specific data of file
> > 	drivers/gpu/drm/amd/amdgpu/../display/dc/dcn31/dcn31_resource.o
> > powerpc64-linux-ld:
> > 	drivers/gpu/drm/amd/amdgpu/../display/dc/dml/display_mode_lib.o
> > 		uses hard float,
> > 	drivers/gpu/drm/amd/amdgpu/../display/dc/dcn315/dcn315_resource.o
> > 		uses soft float
> > powerpc64-linux-ld:
> > 	failed to merge target specific data of
> > 	file drivers/gpu/drm/amd/amdgpu/../display/dc/dcn315/dcn315_resource.o
> > powerpc64-linux-ld:
> > 	drivers/gpu/drm/amd/amdgpu/../display/dc/dml/display_mode_lib.o
> > 		uses hard float,
> > 	drivers/gpu/drm/amd/amdgpu/../display/dc/dcn316/dcn316_resource.o
> > 		uses soft float
> > powerpc64-linux-ld:
> > 	failed to merge target specific data of file
> > 	drivers/gpu/drm/amd/amdgpu/../display/dc/dcn316/dcn316_resource.o
> > 
> > The problem was introduced with commit 41b7a347bf14 ("powerpc: Book3S
> > 64-bit outline-only KASAN support") which adds support for KASAN. This
> > commit in turn enables DRM_AMD_DC_DCN because KCOV_INSTRUMENT_ALL and
> > KCOV_ENABLE_COMPARISONS are no longer enabled. As result, new files are
> > compiled which lack the selection of hard-float.
> > 
> > Fixes: 41b7a347bf14 ("powerpc: Book3S 64-bit outline-only KASAN support")
> > Cc: Michael Ellerman <mpe@ellerman.id.au>
> > Cc: Daniel Axtens <dja@axtens.net>
> > Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> > ---
> >   drivers/gpu/drm/amd/display/dc/dcn31/Makefile  | 4 ++++
> >   drivers/gpu/drm/amd/display/dc/dcn315/Makefile | 4 ++++
> >   drivers/gpu/drm/amd/display/dc/dcn316/Makefile | 4 ++++
> >   3 files changed, 12 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/amd/display/dc/dcn31/Makefile b/drivers/gpu/drm/amd/display/dc/dcn31/Makefile
> > index ec041e3cda30..74be02114ae4 100644
> > --- a/drivers/gpu/drm/amd/display/dc/dcn31/Makefile
> > +++ b/drivers/gpu/drm/amd/display/dc/dcn31/Makefile
> > @@ -15,6 +15,10 @@ DCN31 = dcn31_resource.o dcn31_hubbub.o dcn31_hwseq.o dcn31_init.o dcn31_hubp.o
> >   	dcn31_apg.o dcn31_hpo_dp_stream_encoder.o dcn31_hpo_dp_link_encoder.o \
> >   	dcn31_afmt.o dcn31_vpg.o
> > +ifdef CONFIG_PPC64
> > +CFLAGS_$(AMDDALPATH)/dc/dcn31/dcn31_resource.o := -mhard-float -maltivec
> > +endif
> > +
> >   AMD_DAL_DCN31 = $(addprefix $(AMDDALPATH)/dc/dcn31/,$(DCN31))
> >   AMD_DISPLAY_FILES += $(AMD_DAL_DCN31)
> > diff --git a/drivers/gpu/drm/amd/display/dc/dcn315/Makefile b/drivers/gpu/drm/amd/display/dc/dcn315/Makefile
> > index 59381d24800b..1395c1ced8c5 100644
> > --- a/drivers/gpu/drm/amd/display/dc/dcn315/Makefile
> > +++ b/drivers/gpu/drm/amd/display/dc/dcn315/Makefile
> > @@ -25,6 +25,10 @@
> >   DCN315 = dcn315_resource.o
> > +ifdef CONFIG_PPC64
> > +CFLAGS_$(AMDDALPATH)/dc/dcn315/dcn315_resource.o := -mhard-float -maltivec
> > +endif
> > +
> >   AMD_DAL_DCN315 = $(addprefix $(AMDDALPATH)/dc/dcn315/,$(DCN315))
> >   AMD_DISPLAY_FILES += $(AMD_DAL_DCN315)
> > diff --git a/drivers/gpu/drm/amd/display/dc/dcn316/Makefile b/drivers/gpu/drm/amd/display/dc/dcn316/Makefile
> > index 819d44a9439b..c3d2dd78f1e2 100644
> > --- a/drivers/gpu/drm/amd/display/dc/dcn316/Makefile
> > +++ b/drivers/gpu/drm/amd/display/dc/dcn316/Makefile
> > @@ -25,6 +25,10 @@
> >   DCN316 = dcn316_resource.o
> > +ifdef CONFIG_PPC64
> > +CFLAGS_$(AMDDALPATH)/dc/dcn316/dcn316_resource.o := -mhard-float -maltivec
> > +endif
> > +
> >   AMD_DAL_DCN316 = $(addprefix $(AMDDALPATH)/dc/dcn316/,$(DCN316))
> >   AMD_DISPLAY_FILES += $(AMD_DAL_DCN316)
> 
> Hi,
> 
> I don't want to re-introduce those FPU flags for DCN31/DCN314/DCN316 since
> we fully isolate FPU operations for those ASICs inside the DML folder.

FWIW, I don't think that matters from a linking perspective since the hard-float
and the soft-float objects are linked together, and the linker bails out on
that because the ABIs are not compatible. You only get a warning on that unless
you build with -Werror, which is the case for allmodconfig builds.

Guenter