On Fri, 22 Jul 2022 22:32:06 +1000
Michael Ellerman <mich...@ellerman.id.au> wrote:
> Hi Dan,
>
> [ Cc += linuxppc-dev ]
>
> Dan Horák <d...@danny.cz> writes:
> > Commit d11219ad53dc disabled the DCN driver for all platforms that
> > define PPC64 due long build issues during "make allmodconfig" using
> > cross-compilation. Cross-compilation defaults to the ppc64_defconfig
> > and thus big-endian toolchain configuration. The ppc64le platform uses a
> > different ABI and doesn't suffer from the build issues.
>
> Unfortunately it's a bit messier than that.
yes, seems it is :-)
> The build error occurs when the compiler is built to use a 64-bit long
> double type.
>
> The ppc64le ABI document says that long double should be 128-bits, but
> there are ppc64le compilers out there that are configured to use 64-bit
> long double, notably the kernel.org crosstool compilers.
>
> So just testing for CPU_LITTLE_ENDIAN means we'll still get build errors
> on those compilers.
>
> But I think we can detect the long double size and key off that. Can you
> test the patch below works for you?
yes, it does work, meaning it defines AMD_DC_DCN on Fedora/ppc64le (and
build is OK)
Dan
>
> cheers
>
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 7aa12e88c580..e9f8cd50af99 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -281,6 +281,9 @@ config PPC
> # Please keep this list sorted alphabetically.
> #
>
> +config PCC_LONG_DOUBLE_128
> + def_bool $(success,test "$(shell,echo __LONG_DOUBLE_128__ | $(CC) -E -P
> -)" = 1)
> +
> config PPC_BARRIER_NOSPEC
> bool
> default y
> diff --git a/drivers/gpu/drm/amd/display/Kconfig
> b/drivers/gpu/drm/amd/display/Kconfig
> index b4029c0d5d8c..ec6771e87e73 100644
> --- a/drivers/gpu/drm/amd/display/Kconfig
> +++ b/drivers/gpu/drm/amd/display/Kconfig
> @@ -6,7 +6,7 @@ config DRM_AMD_DC
> bool "AMD DC - Enable new display engine"
> default y
> select SND_HDA_COMPONENT if SND_HDA_CORE
> - select DRM_AMD_DC_DCN if (X86 || PPC64) && !(KCOV_INSTRUMENT_ALL &&
> KCOV_ENABLE_COMPARISONS)
> + select DRM_AMD_DC_DCN if (X86 || PPC_LONG_DOUBLE_128) &&
> !(KCOV_INSTRUMENT_ALL && KCOV_ENABLE_COMPARISONS)
> help
> Choose this option if you want to use the new display engine
> support for AMDGPU. This adds required support for Vega and
