Re: [PATCH v4 13/15] drm/amd/display: Use ARCH_HAS_KERNEL_FPU_SUPPORT

From: Samuel Holland <samuel.holland@sifive.com>
To: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-arm-kernel@lists.infradead.org, x86@kernel.org,
	linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
	Christoph Hellwig <hch@lst.de>,
	loongarch@lists.linux.dev, amd-gfx@lists.freedesktop.org,
	Alex Deucher <alexander.deucher@amd.com>
Subject: Re: [PATCH v4 13/15] drm/amd/display: Use ARCH_HAS_KERNEL_FPU_SUPPORT
Date: Wed, 10 Apr 2024 17:47:27 -0500	[thread overview]
Message-ID: <75a37a4b-f516-40a3-b6b5-4aa1636f9b60@sifive.com> (raw)
In-Reply-To: <87wmp4oo3y.fsf@linaro.org>

Hi Thiago,

On 2024-04-10 5:21 PM, Thiago Jung Bauermann wrote:
> Samuel Holland <samuel.holland@sifive.com> writes:
> 
>> Now that all previously-supported architectures select
>> ARCH_HAS_KERNEL_FPU_SUPPORT, this code can depend on that symbol instead
>> of the existing list of architectures. It can also take advantage of the
>> common kernel-mode FPU API and method of adjusting CFLAGS.
>>
>> Acked-by: Alex Deucher <alexander.deucher@amd.com>
>> Reviewed-by: Christoph Hellwig <hch@lst.de>
>> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
> 
> Unfortunately this patch causes build failures on arm with allyesconfig
> and allmodconfig. Tested with next-20240410.
> 
> Error with allyesconfig:
> 
> $ make -j 8 \
>     O=$HOME/.cache/builds/linux-cross-arm \
>     ARCH=arm \
>     CROSS_COMPILE=arm-linux-gnueabihf-
> make[1]: Entering directory '/home/bauermann/.cache/builds/linux-cross-arm'
>     ⋮
> arm-linux-gnueabihf-ld: drivers/gpu/drm/amd/display/dc/dml/dcn20/dcn20_fpu.o: in function `dcn20_populate_dml_pipes_from_context':
> dcn20_fpu.c:(.text+0x20f4): undefined reference to `__aeabi_l2d'
> arm-linux-gnueabihf-ld: dcn20_fpu.c:(.text+0x210c): undefined reference to `__aeabi_l2d'
> arm-linux-gnueabihf-ld: dcn20_fpu.c:(.text+0x2124): undefined reference to `__aeabi_l2d'
> arm-linux-gnueabihf-ld: dcn20_fpu.c:(.text+0x213c): undefined reference to `__aeabi_l2d'
> arm-linux-gnueabihf-ld: drivers/gpu/drm/amd/display/dc/dml/calcs/dcn_calcs.o: in function `pipe_ctx_to_e2e_pipe_params':
> dcn_calcs.c:(.text+0x390): undefined reference to `__aeabi_l2d'
> arm-linux-gnueabihf-ld: drivers/gpu/drm/amd/display/dc/dml/calcs/dcn_calcs.o:dcn_calcs.c:(.text+0x3a4): more undefined references to `__aeabi_l2d' follow
> arm-linux-gnueabihf-ld: drivers/gpu/drm/amd/display/dc/dml2/dml2_wrapper.o: in function `optimize_configuration':
> dml2_wrapper.c:(.text+0xcbc): undefined reference to `__aeabi_d2ulz'
> arm-linux-gnueabihf-ld: drivers/gpu/drm/amd/display/dc/dml2/dml2_translation_helper.o: in function `populate_dml_plane_cfg_from_plane_state':
> dml2_translation_helper.c:(.text+0x9e4): undefined reference to `__aeabi_l2d'
> arm-linux-gnueabihf-ld: dml2_translation_helper.c:(.text+0xa20): undefined reference to `__aeabi_l2d'
> arm-linux-gnueabihf-ld: dml2_translation_helper.c:(.text+0xa58): undefined reference to `__aeabi_l2d'
> arm-linux-gnueabihf-ld: dml2_translation_helper.c:(.text+0xa90): undefined reference to `__aeabi_l2d'
> make[3]: *** [/home/bauermann/src/linux/scripts/Makefile.vmlinux:37: vmlinux] Error 1
> make[2]: *** [/home/bauermann/src/linux/Makefile:1165: vmlinux] Error 2
> make[1]: *** [/home/bauermann/src/linux/Makefile:240: __sub-make] Error 2
> make[1]: Leaving directory '/home/bauermann/.cache/builds/linux-cross-arm'
> make: *** [Makefile:240: __sub-make] Error 2
> 
> The error with allmodconfig is slightly different:
> 
> $ make -j 8 \
>     O=$HOME/.cache/builds/linux-cross-arm \
>     ARCH=arm \
>     CROSS_COMPILE=arm-linux-gnueabihf-
> make[1]: Entering directory '/home/bauermann/.cache/builds/linux-cross-arm'
>     ⋮
> ERROR: modpost: "__aeabi_d2ulz" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!
> ERROR: modpost: "__aeabi_l2d" [drivers/gpu/drm/amd/amdgpu/amdgpu.ko] undefined!
> make[3]: *** [/home/bauermann/src/linux/scripts/Makefile.modpost:145: Module.symvers] Error 1
> make[2]: *** [/home/bauermann/src/linux/Makefile:1876: modpost] Error 2
> make[1]: *** [/home/bauermann/src/linux/Makefile:240: __sub-make] Error 2
> make[1]: Leaving directory '/home/bauermann/.cache/builds/linux-cross-arm'
> make: *** [Makefile:240: __sub-make] Error 2

In both cases, the issue is that the toolchain requires runtime support to
convert between `unsigned long long` and `double`, even when hardware FP is
enabled. There was some past discussion about GCC inlining some of these
conversions[1], but that did not get implemented.

The short-term fix would be to drop the `select ARCH_HAS_KERNEL_FPU_SUPPORT` for
32-bit arm until we can provide these runtime library functions.

Regards,
Samuel

[1]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91970