On Mon, 25 Jul 2022 22:39:18 +1000
Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote:
> Commit d11219ad53dc ("amdgpu: disable powerpc support for the newer
> display engine") disabled the DCN driver for all of powerpc due to
> unresolved build failures with some compilers.
>
> Further digging shows that the build failures only occur with compilers
> that default to 64-bit long double.
>
> Both the ppc64 and ppc64le ABIs define long double to be 128-bits, but
> there are compilers in the wild that default to 64-bits. The compilers
> provided by the major distros (Fedora, Ubuntu) default to 128-bits and
> are not affected by the build failure.
>
> There is a compiler flag to force 128-bit long double, which may be the
> correct long term fix, but as an interim fix only allow building the DCN
> driver if long double is 128-bits by default.
>
> The bisection in commit d11219ad53dc must have gone off the rails at
> some point, the build failure occurs all the way back to the original
> commit that enabled DCN support on powerpc, at least with some
> toolchains.
>
> Depends-on: d11219ad53dc ("amdgpu: disable powerpc support for the newer display engine")
> Fixes: 16a9dea110a6 ("amdgpu: Enable initial DCN support on POWER")
> Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2100
LGTM
Reviewed-by: Dan Horák <dan@xxxxxxxx>
Dan
> ---
> arch/powerpc/Kconfig | 4 ++++
> drivers/gpu/drm/amd/display/Kconfig | 2 +-
> 2 files changed, 5 insertions(+), 1 deletion(-)
>
> Alex, are you OK if I take this via the powerpc tree for v5.19?
>
> cheers
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 7aa12e88c580..287cc2d4a4b3 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -281,6 +281,10 @@ config PPC
> # Please keep this list sorted alphabetically.
> #
>
> +config PPC_LONG_DOUBLE_128
> + depends on PPC64
> + 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 0ba0598eba20..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 && !(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
> --
> 2.35.3
>
