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

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Message-ID: <CAK8P3a0Zi2MAzG2f6Te-LYuDuLd4yiy4b3VRYQY6EspqzMnQ5w@mail.gmail.com>
Date:   Thu, 25 Feb 2021 22:36:04 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Bindu Ramamurthy <bindu.r@....com>,
        Vladimir Stempen <vladimir.stempen@....com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
        Dmytro Laktyushkin <Dmytro.Laktyushkin@....com>,
        Aurabindo Pillai <aurabindo.pillai@....com>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/amd/display: fix 64-bit integer division

On Thu, Feb 25, 2021 at 3:33 PM Arnd Bergmann <arnd@...nel.org> wrote:
>
> From: Arnd Bergmann <arnd@...db.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