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

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

On 7/13/22 13:57, Alex Deucher wrote:
> On Thu, Jun 30, 2022 at 5:01 PM Rodrigo Siqueira Jordao
> <Rodrigo.Siqueira@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@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
> 
> 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@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.

Guenter