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

[Alex Deucher]

On Wed, Jul 13, 2022 at 5:18 PM Guenter Roeck <linux at roeck-us.net> wrote:
>
> On 7/13/22 13:57, Alex Deucher wrote:
> > On Thu, Jun 30, 2022 at 5:01 PM Rodrigo Siqueira Jordao
> > <Rodrigo.Siqueira at amd.com> 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 at ellerman.id.au>
> >>> Cc: Daniel Axtens <dja at axtens.net>
> >>> Signed-off-by: Guenter Roeck <linux at 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
> >
> > I don't understand why we don't need to add the hard-float flags back
> > on the other DCN blocks.  Did we miss something in the DML cleanup for
> > DCN 3.1.x?  Anyway, at this point, the patch is:
> > Acked-by: Alex Deucher <alexander.deucher at amd.com>
> > We can sort the rest out for 5.20.
> >
>
> The problem is not the FPU operations, but the fact that soft-float
> and hard-float compiled code is linked together. The soft-float and
> hard-float ABIs on powerpc are not compatible, so one ends up with
> an object file which is partially soft-float and partially hard-float
> compiled and thus uses different ABIs. That can only create chaos,
> so the linker complains about it.

I get that, I just don't see why only DCN 3.1.x files have this
problem.  The DCN 2.x files should as well.

Alex