linux-kernel - Re: [PATCH] drm/amd/amdgpu: enable W=1 for amdgpu

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Message-ID: <CAK7LNAQArK=+Qy+yQU2qB-0pCKyWugsQ=VGXUzLUf+tPow5M_w@mail.gmail.com>
Date:   Sat, 10 Jun 2023 10:20:27 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Hamza Mahfooz <hamza.mahfooz@....com>,
        amd-gfx@...ts.freedesktop.org,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Hawking Zhang <Hawking.Zhang@....com>, Le Ma <le.ma@....com>,
        Tao Zhou <tao.zhou1@....com>,
        YiPeng Chai <YiPeng.Chai@....com>,
        James Zhu <James.Zhu@....com>,
        Xiaojian Du <Xiaojian.Du@....com>,
        Lijo Lazar <lijo.lazar@....com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-kbuild@...r.kernel.org
Subject: Re: [PATCH] drm/amd/amdgpu: enable W=1 for amdgpu

On Sat, Jun 10, 2023 at 5:17 AM Nathan Chancellor <nathan@...nel.org> wrote:
>
> + Masahiro and linux-kbuild
>
> On Fri, Jun 09, 2023 at 12:42:06PM -0400, Hamza Mahfooz wrote:
> > We have a clean build with W=1 as of
> > commit 12a15dd589ac ("drm/amd/display/amdgpu_dm/amdgpu_dm_helpers: Move
> > SYNAPTICS_DEVICE_ID into CONFIG_DRM_AMD_DC_DCN ifdef"). So, let's enable
> > these checks unconditionally for the entire module to catch these errors
> > during development.
> >
> > Cc: Alex Deucher <alexander.deucher@....com>
> > Cc: Nathan Chancellor <nathan@...nel.org>
> > Signed-off-by: Hamza Mahfooz <hamza.mahfooz@....com>
>
> I think this is fine, especially since it will help catch issues in
> amdgpu quickly and hopefully encourage developers to fix their problems
> before they make it to a tree with wider impact lika -next.
>
> However, this is now the third place that W=1 has been effectively
> enabled (i915 and btrfs are the other two I know of) and it would be
> nice if this was a little more unified, especially since it is not
> uncommon for the warnings under W=1 to shift around and keeping them
> unified will make maintainence over the longer term a little easier. I
> am not sure if this has been brought up in the past and I don't want to
> hold up this change but I suspect this sentiment of wanting to enable
> W=1 on a per-subsystem basis is going to continue to grow.



I believe this patch is the right way because
we will be able to add a new warning option to
scripts/Makefile.extrawarn without fixing any code.

I remember somebody argued that drivers should be
able to do
  subdir-ccflags-y += $(W1_FLAGS)

However, if a new flag, -Wfoo, emits warnings
for drivers/gpu/drm/{i915,amd},
you cannot add it to W=1 until fixing the code.

If many drivers start to do likewise,
W=1 warning will not be W=1 any more.



Another good thing for hard-coding warning options
is you can lift up a warning flag one by one.


Let's say you fixed the entire DRM subsystem so
it is -Wunused free now.

Then, you can move -Wunused to drivers/gpu/drm/Makefile,
while other warning options stay in drivers Makefiles.







>
> Regardless, for clang 11.1.0 to 16.0.5, I see no warnings when building
> drivers/gpu/drm/amd/amdgpu/ with Arch Linux's configuration or
> allmodconfig.
>
> Reviewed-by: Nathan Chancellor <nathan@...nel.org>
> Tested-by: Nathan Chancellor <nathan@...nel.org>
>
> > ---
> >  drivers/gpu/drm/amd/amdgpu/Makefile | 13 ++++++++++++-
> >  1 file changed, 12 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/amd/amdgpu/Makefile b/drivers/gpu/drm/amd/amdgpu/Makefile
> > index 86b833085f19..8d16f280b695 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/Makefile
> > +++ b/drivers/gpu/drm/amd/amdgpu/Makefile
> > @@ -40,7 +40,18 @@ ccflags-y := -I$(FULL_AMD_PATH)/include/asic_reg \
> >       -I$(FULL_AMD_PATH)/amdkfd
> >
> >  subdir-ccflags-y := -Wextra
> > -subdir-ccflags-y += $(call cc-option, -Wunused-but-set-variable)
> > +subdir-ccflags-y += -Wunused
> > +subdir-ccflags-y += -Wmissing-prototypes
> > +subdir-ccflags-y += -Wmissing-declarations
> > +subdir-ccflags-y += -Wmissing-include-dirs
> > +subdir-ccflags-y += -Wold-style-definition
> > +subdir-ccflags-y += -Wmissing-format-attribute
> > +# Need this to avoid recursive variable evaluation issues
> > +cond-flags := $(call cc-option, -Wunused-but-set-variable) \
> > +     $(call cc-option, -Wunused-const-variable) \
> > +     $(call cc-option, -Wstringop-truncation) \
> > +     $(call cc-option, -Wpacked-not-aligned)
> > +subdir-ccflags-y += $(cond-flags)
> >  subdir-ccflags-y += -Wno-unused-parameter
> >  subdir-ccflags-y += -Wno-type-limits
> >  subdir-ccflags-y += -Wno-sign-compare
> > --
> > 2.40.1
> >



-- 
Best Regards
Masahiro Yamada