Commit c653c591789b ("drm/amdgpu: Re-enable DCN for 64-bit powerpc") introduced this check as a workaround for the driver not building with toolchains that default to 64-bit long double.
The reason things worked on 128-bit-long-double toolchains and not otherwise was however largely accidental. The real issue was that some files containing floating point code were compiled without -mhard-float, while others were compiled with -mhard-float.
The PowerPC compilers tag object files that use long doubles with a special ABI tag in order to differentiate 64-bit long double, IBM long double and IEEE 128-bit long double. When no long double is used in a source file, the file does not receive the ABI tag. Since only regular doubles are used in the AMDGPU source, there is no ABI tag on the soft-float object files with 128-bit-ldbl compilers, and therefore no error. With 64-bit long double, the double and long double types are equal, and an ABI tag is introduced.
Of course, this resulted in the real bug, which was mixing of hard and soft float object files, getting hidden, which makes this check technically incorrect.
Since then, work has been done to ensure that all float code is separately compiled. This was also necessary in order to enable AArch64 support in the display stack, as AArch64 does not have any soft-float ABI, and all code that does not explicitly conatain floats is compiled with -mgeneral-regs-only, which prevents float-using code from being compiled at all. That means AArch64 support will from now on always safeguard against such cases happening ever again.
In mainline, this work is now fully done, so this check is fully redundant and does not do anything except preventing AMDGPU DC from being built on systems such as those using musl libc. The last piece of work to enable this was commit c92b7fe0d92a ("drm/amd/display: move remaining FPU code to dml folder") and this has since been backported to 6.1 stable (in 6.1.7).
Relevant issue: https://gitlab.freedesktop.org/drm/amd/-/issues/2288
Signed-off-by: Daniel Kolesa daniel@octaforge.org --- arch/powerpc/Kconfig | 4 ---- drivers/gpu/drm/amd/display/Kconfig | 2 +- 2 files changed, 1 insertion(+), 5 deletions(-)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index b8c4ac56b..267805072 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig @@ -289,10 +289,6 @@ config PPC # Please keep this list sorted alphabetically. #
-config PPC_LONG_DOUBLE_128 - depends on PPC64 && ALTIVEC - 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 2efe93f74..94645b6ef 100644 --- a/drivers/gpu/drm/amd/display/Kconfig +++ b/drivers/gpu/drm/amd/display/Kconfig @@ -8,7 +8,7 @@ config DRM_AMD_DC depends on BROKEN || !CC_IS_CLANG || X86_64 || SPARC64 || ARM64 select SND_HDA_COMPONENT if SND_HDA_CORE # !CC_IS_CLANG: https://github.com/ClangBuiltLinux/linux/issues/1752 - select DRM_AMD_DC_DCN if (X86 || PPC_LONG_DOUBLE_128 || (ARM64 && KERNEL_MODE_NEON && !CC_IS_CLANG)) + select DRM_AMD_DC_DCN if (X86 || PPC64 || (ARM64 && KERNEL_MODE_NEON && !CC_IS_CLANG)) help Choose this option if you want to use the new display engine support for AMDGPU. This adds required support for Vega and
Hi,
Thanks for your patch.
FYI: kernel test robot notices the stable kernel rule is not satisfied.
Rule: 'Cc: stable@vger.kernel.org' or 'commit <sha1> upstream.' Subject: [PATCH] drm/amdgpu: drop the long-double-128 powerpc check/hack Link: https://lore.kernel.org/stable/dab9cbd8-2626-4b99-8098-31fe76397d2d%40app.fa...
The check is based on https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
[Public]
-----Original Message----- From: amd-gfx amd-gfx-bounces@lists.freedesktop.org On Behalf Of Daniel Kolesa Sent: Wednesday, February 1, 2023 1:46 PM To: linuxppc-dev@lists.ozlabs.org Cc: dan@danny.cz; stable@vger.kernel.org; tpearson@raptorengineering.com; amd-gfx@lists.freedesktop.org; alexdeucher@gmail.com; torvalds@linux-foundation.org Subject: [PATCH] drm/amdgpu: drop the long-double-128 powerpc check/hack
Commit c653c591789b ("drm/amdgpu: Re-enable DCN for 64-bit powerpc") introduced this check as a workaround for the driver not building with toolchains that default to 64-bit long double.
The reason things worked on 128-bit-long-double toolchains and not otherwise was however largely accidental. The real issue was that some files containing floating point code were compiled without -mhard-float, while others were compiled with -mhard-float.
The PowerPC compilers tag object files that use long doubles with a special ABI tag in order to differentiate 64-bit long double, IBM long double and IEEE 128-bit long double. When no long double is used in a source file, the file does not receive the ABI tag. Since only regular doubles are used in the AMDGPU source, there is no ABI tag on the soft-float object files with 128-bit-ldbl compilers, and therefore no error. With 64-bit long double, the double and long double types are equal, and an ABI tag is introduced.
Of course, this resulted in the real bug, which was mixing of hard and soft float object files, getting hidden, which makes this check technically incorrect.
Since then, work has been done to ensure that all float code is separately compiled. This was also necessary in order to enable AArch64 support in the display stack, as AArch64 does not have any soft-float ABI, and all code that does not explicitly conatain floats is compiled with - mgeneral-regs-only, which prevents float-using code from being compiled at all. That means AArch64 support will from now on always safeguard against such cases happening ever again.
In mainline, this work is now fully done, so this check is fully redundant and does not do anything except preventing AMDGPU DC from being built on systems such as those using musl libc. The last piece of work to enable this was commit c92b7fe0d92a ("drm/amd/display: move remaining FPU code to dml folder") and this has since been backported to 6.1 stable (in 6.1.7).
Relevant issue: https://gitlab.freedesktop.org/drm/amd/-/issues/2288
Signed-off-by: Daniel Kolesa daniel@octaforge.org
Acked-by: Alex Deucher alexander.deucher@amd.com
arch/powerpc/Kconfig | 4 ---- drivers/gpu/drm/amd/display/Kconfig | 2 +- 2 files changed, 1 insertion(+), 5 deletions(-)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index b8c4ac56b..267805072 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig @@ -289,10 +289,6 @@ config PPC # Please keep this list sorted alphabetically. #
-config PPC_LONG_DOUBLE_128
- depends on PPC64 && ALTIVEC
- 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 2efe93f74..94645b6ef 100644 --- a/drivers/gpu/drm/amd/display/Kconfig +++ b/drivers/gpu/drm/amd/display/Kconfig @@ -8,7 +8,7 @@ config DRM_AMD_DC depends on BROKEN || !CC_IS_CLANG || X86_64 || SPARC64 || ARM64 select SND_HDA_COMPONENT if SND_HDA_CORE # !CC_IS_CLANG: https://github.com/ClangBuiltLinux/linux/issues/1752
- select DRM_AMD_DC_DCN if (X86 || PPC_LONG_DOUBLE_128 ||
(ARM64 && KERNEL_MODE_NEON && !CC_IS_CLANG))
- select DRM_AMD_DC_DCN if (X86 || PPC64 || (ARM64 &&
KERNEL_MODE_NEON +&& !CC_IS_CLANG)) help Choose this option if you want to use the new display engine support for AMDGPU. This adds required support for Vega and -- 2.34.1
linux-stable-mirror@lists.linaro.org
-
Daniel Kolesa -
Deucher, Alexander -
kernel test robot