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

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

On 6/30/22 14:01, 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. Notice that we have the PPC64 in the DML Makefile:
> 
> https://gitlab.freedesktop.org/agd5f/linux/-/blob/amd-staging-drm-next/drivers/gpu/drm/amd/display/dc/dml/Makefile
> 

Yes, sure, ppc64 is in dc/dml/Makefile. The problem is that it selects hard-float

ifdef CONFIG_PPC64
dml_ccflags := -mhard-float -maltivec
endif

and dc/{dcn31,dcn315,dcn316} don't.


> Could you share what you see without your patch in the amd-staging-drm-next?

You mean linux-next ? Same error.

Building powerpc:allmodconfig ... failed
--------------
Error log:
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

This isn't really surprising since dc/dml/ does build with hard float, and
dc/{dcn31,dcn315,dcn316} build with soft float. As mentioned above,
the problem is now seen because DRM_AMD_DC_DCN is now enabled which was
previously not the case.

select DRM_AMD_DC_DCN if (X86 || PPC64) && !(KCOV_INSTRUMENT_ALL && KCOV_ENABLE_COMPARISONS)
                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Up to v5.18, both KCOV_INSTRUMENT_ALL and KCOV_ENABLE_COMPARISONS were enabled
and DRM_AMD_DC_DCN was therefore disabled. Now KCOV_INSTRUMENT_ALL and
KCOV_ENABLE_COMPARISONS are disabled, which results in DRM_AMD_DC_DCN=y.
This in turn results in the hard/soft float inconsistencies and the compile
failure.

  Also:
> * Are you using cross-compilation? If so, could you share your setup?
> * Which GCC/Clang version are you using?

gcc 11.2.0 with binutils 2.36.1, but that really does not make a difference.

Guenter