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

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Message-ID: <20241218190558.g2hykmjgbny4n5i3@jpoimboe>
Date: Wed, 18 Dec 2024 11:05:58 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: 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 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.

-- 
Josh