linux-kernel - Re: [PATCH] drm/amd/display: Add missing hard-float compile flags for PPC64 builds

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Message-ID: <20220713230917.GE32544@roeck-us.net>
Date:   Wed, 13 Jul 2022 16:09:17 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Alex Deucher <alexdeucher@...il.com>
Cc:     Rodrigo Siqueira Jordao <Rodrigo.Siqueira@....com>,
        Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        Michael Ellerman <mpe@...erman.id.au>,
        LKML <linux-kernel@...r.kernel.org>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        David Airlie <airlied@...ux.ie>,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        Daniel Axtens <dja@...ens.net>
Subject: Re: [PATCH] drm/amd/display: Add missing hard-float compile flags
 for PPC64 builds

On Wed, Jul 13, 2022 at 05:20:40PM -0400, Alex Deucher wrote:
> >
> > The problem is not the FPU operations, but the fact that soft-float
> > and hard-float compiled code is linked together. The soft-float and
> > hard-float ABIs on powerpc are not compatible, so one ends up with
> > an object file which is partially soft-float and partially hard-float
> > compiled and thus uses different ABIs. That can only create chaos,
> > so the linker complains about it.
> 
> I get that, I just don't see why only DCN 3.1.x files have this
> problem.  The DCN 2.x files should as well.
> 

Seen in drivers/gpu/drm/amd/display/dc/clk_mgr/Makefile:

# prevent build errors regarding soft-float vs hard-float FP ABI tags
# this code is currently unused on ppc64, as it applies to Renoir APUs only
ifdef CONFIG_PPC64
CFLAGS_$(AMDDALPATH)/dc/clk_mgr/dcn21/rn_clk_mgr.o := $(call cc-option,-mno-gnu-attribute)
endif

Does that explain it ?

Guenter