linux-kernel - Re: [PATCH] drm/amdgpu: make DRM_AMD

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Date:   Mon, 7 Dec 2020 14:07:53 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Christian König <christian.koenig@....com>,
        Alex Deucher <alexdeucher@...il.com>,
        Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        Alex Deucher <alexander.deucher@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Nathan Chancellor <natechancellor@...il.com>,
        Luben Tuikov <luben.tuikov@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Mauro Rossi <issor.oruam@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Roman Li <Roman.Li@....com>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>,
        Bhawanpreet Lakha <Bhawanpreet.Lakha@....com>,
        Daniel Kolesa <daniel@...aforge.org>,
        Timothy Pearson <tpearson@...torengineering.com>
Subject: Re: [PATCH] drm/amdgpu: make DRM_AMD_DC x86-only again

On Mon, Dec 7, 2020 at 1:57 PM Arnd Bergmann <arnd@...nel.org> wrote:
>
> On Mon, Dec 7, 2020 at 9:50 PM Christian König <christian.koenig@....com> wrote:
> > Am 07.12.20 um 21:47 schrieb Alex Deucher:
> > > On Fri, Dec 4, 2020 at 3:13 AM Arnd Bergmann <arnd@...nel.org> wrote:
> > >> From: Arnd Bergmann <arnd@...db.de>
> > >>
> > >> As the DRM_AMD_DC_DCN3_0 code was x86-only and fails to build on
> > >> arm64, merging it into DRM_AMD_DC means that the top-level symbol
> > >> is now x86-only as well.
> > >>
> > >> Compilation fails on arm64 with clang-12 with
> > >>
> > >> drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn30/display_mode_vba_30.c:3641:6: error: stack frame size of 2416 bytes in function 'dml30_ModeSupportAndSystemConfigurationFull' [-Werror,-Wframe-larger-than=]
> > >> void dml30_ModeSupportAndSystemConfigurationFull(struct display_mode_lib *mode_lib)
> > >>
> > >> I tried to see if the stack usage can be reduced, but this is code
> > >> that is described as "This file is gcc-parsable HW gospel, coming
> > >> straight from HW engineers." and is written in a way that is inherently
> > >> nonportable and not meant to be understood by humans.
> > >>
> > >> There are probably no non-x86 users of this code, so simplify
> > >> the dependency list accordingly.
> > > + Daniel, Timothy
> > >
> > > Others contributed code to enable this on PPC64 and ARM64.
> > > Unfortunately, we don't have these platforms to test with within AMD.
> > > Does PPC64 have the same stack limitations as ARM64?  Harry, Leo, can
> > > you take a look at fixing the stack usage?
> >
> > This reminds me that I wanted to reply on this.
> >
> > 2416 is even to much on x86 if you add -Werror :)
> >
> > So this needs to be fixed anyway.
>
> Right, looking at my latest randconfig logs, I see the same problem on x86
> builds with clang as well, though I'm not entirely sure which other
> configuration
> options are needed to trigger it.
>
> So my patch can be disregarded, but I agree this needs a better fix,
> either in clang or in the dcn driver.

If you could give https://github.com/ClangBuiltLinux/frame-larger-than
a spin again, I would appreciate any feedback.


-- 
Thanks,
~Nick Desaulniers