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

[Jani Nikula <jani.nikula@linux.intel.com>]

On Sat, 10 Jun 2023, Masahiro Yamada <masahiroy@kernel.org> wrote:
> On Sat, Jun 10, 2023 at 5:17 AM Nathan Chancellor <nathan@kernel.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@amd.com>
>> > Cc: Nathan Chancellor <nathan@kernel.org>
>> > Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.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)

Personally, I think this would be the viable way to make the kernel free
of W=1 warnings. Make it clean driver and subsystem at a time, with
constant progress. Currently, there's haphazard fixing of issues, with
new ones creeping back in, because kernel-wide W=1 is too verbose for
most developers. It's whac-a-mole.

> 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.

Or adding -Wno-foo where it breaks, until fixed.

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

I don't know, is the goal to fix the warnings, or keep adding stuff to
W=1 so that it'll always emit warnings? :p


BR,
Jani.

> 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@kernel.org>
>> Tested-by: Nathan Chancellor <nathan@kernel.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
>> >

-- 
Jani Nikula, Intel Open Source Graphics Center