[PATCH] drm/amd/display: fix 64-bit integer division

[Arnd Bergmann]

On Thu, Feb 25, 2021 at 3:33 PM Arnd Bergmann <arnd at kernel.org> wrote:
>
> From: Arnd Bergmann <arnd at arndb.de>
>
> The new display synchronization code caused a regression
> on all 32-bit architectures:
>
> ld.lld: error: undefined symbol: __aeabi_uldivmod
> >>> referenced by dce_clock_source.c
> >>>               gpu/drm/amd/display/dc/dce/dce_clock_source.o:(get_pixel_clk_frequency_100hz) in archive drivers/built-in.a
>
> ld.lld: error: undefined symbol: __aeabi_ldivmod
> >>> referenced by dc_resource.c
> >>>               gpu/drm/amd/display/dc/core/dc_resource.o:(resource_are_vblanks_synchronizable) in archive drivers/built-in.a
> >>> referenced by dc_resource.c
> >>>               gpu/drm/amd/display/dc/core/dc_resource.o:(resource_are_vblanks_synchronizable) in archive drivers/built-in.a
> >>> referenced by dc_resource.c
> >>>               gpu/drm/amd/display/dc/core/dc_resource.o:(resource_are_vblanks_synchronizable) in archive drivers/built-in.a
>
> This is not a fast path, so the use of an explicit div_u64/div_s64
> seems appropriate.

I found two more instances:

>>> referenced by dcn20_optc.c
>>>               gpu/drm/amd/display/dc/dcn20/dcn20_optc.o:(optc2_align_vblanks) in archive drivers/built-in.a

>>> referenced by dcn10_hw_sequencer.c
>>>               gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.o:(reduceSizeAndFraction) in archive drivers/built-in.a

I have patches for both, but will let the randconfig build box keep working
on it over night to see if there are any others. Let me know if you want a
combined patch or one per file once there are no more regressions.

        Arnd