linux-kernel - Re: [PATCH v6 9/9] drm/amd/display: Mark dc_fixpt_from

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Message-ID: <CADnq5_PFcHzob4poLa86_K4yP5gUT7Ei4Rz5vSUofvZTmB48-g@mail.gmail.com>
Date: Wed, 18 Dec 2024 14:22:10 -0500
From: Alex Deucher <alexdeucher@...il.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Huacai Chen <chenhuacai@...nel.org>, Tiezhu Yang <yangtiezhu@...ngson.cn>, 
	Peter Zijlstra <peterz@...radead.org>, loongarch@...ts.linux.dev, 
	amd-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 9/9] drm/amd/display: Mark dc_fixpt_from_fraction() noinline

On Wed, Dec 18, 2024 at 2:18 PM Josh Poimboeuf <jpoimboe@...nel.org> wrote:
>
> On Wed, Dec 18, 2024 at 10:36:00PM +0800, Huacai Chen wrote:
> > Hi, Tiezhu,
> >
> > On Tue, Dec 17, 2024 at 9:50 AM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
> > >
> > > When compiling with Clang on LoongArch, there exists the following objtool
> > > warning in drivers/gpu/drm/amd/display/dc/basics/fixpt31_32.o:
> > >
> > >   dc_fixpt_recip() falls through to next function dc_fixpt_sinc()
> > >
> > > This is because dc_fixpt_from_fraction() is inlined in dc_fixpt_recip()
> > > by Clang, given dc_fixpt_from_fraction() is not a simple function, just
> > > mark it noinline to avoid the above issue.
> > I don't know whether drm maintainers can accept this, because it looks
> > like a workaround. Yes, uninline this function "solve" a problem and
> > seems reasonable in this case because the function is "not simple",
> > but from another point of view, you may hide a type of bug.
>
> Agreed, it sounds like there's definitely a bug which this patch is
> papering over.

Yes, agreed.

Alex

>
> --
> Josh