[RFC] drm: enable W=1 warnings by default across the subsystem

[Hamza Mahfooz]

Cc: Nathan Chancellor <nathan at kernel.org>

On 11/29/23 13:12, Jani Nikula wrote:
> At least the i915 and amd drivers enable a bunch more compiler warnings
> than the kernel defaults.
> 
> Extend the W=1 warnings to the entire drm subsystem by default. Use the
> copy-pasted warnings from scripts/Makefile.extrawarn with
> s/KBUILD_CFLAGS/subdir-ccflags-y/ to make it easier to compare and keep
> up with them in the future.
> 
> This is similar to the approach currently used in i915.
> 
> Some of the -Wextra warnings do need to be disabled, just like in
> Makefile.extrawarn, but take care to not disable them for W=2 or W=3
> builds, depending on the warning.

I think this should go in after drm-misc-next has a clean build (for
COMPILE_TEST builds) with this patch applied. Otherwise, it will break a
lot of build configs.

> 
> Cc: David Airlie <airlied at gmail.com>
> Cc: Daniel Vetter <daniel at ffwll.ch>
> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Cc: Maxime Ripard <mripard at kernel.org>
> Cc: Thomas Zimmermann <tzimmermann at suse.de>
> Cc: Alex Deucher <alexander.deucher at amd.com>
> Cc: Christian König <christian.koenig at amd.com>
> Cc: Pan, Xinhui <Xinhui.Pan at amd.com>
> Cc: Karol Herbst <kherbst at redhat.com>
> Cc: Lyude Paul <lyude at redhat.com>
> Cc: Danilo Krummrich <dakr at redhat.com>
> Cc: Rob Clark <robdclark at gmail.com>
> Cc: Abhinav Kumar <quic_abhinavk at quicinc.com>
> Cc: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
> Cc: Sean Paul <sean at poorly.run>
> Cc: Marijn Suijten <marijn.suijten at somainline.org>
> Signed-off-by: Jani Nikula <jani.nikula at intel.com>
> 
> ---
> 
> With my admittedly limited and very much x86 focused kernel config, I
> get some -Wunused-but-set-variable and -Wformat-truncation= warnings,
> but nothing we can't handle.
> 
> We could fix them up front, or disable the extra warnings on a per
> driver basis with a FIXME comment in their respective Makefiles.
> 
> With the experience from i915, I think this would significantly reduce
> the constant loop of warnings added by people not using W=1 and
> subsequently fixed by people using W=1.
> 
> Note: I've Cc'd the maintainers of drm, drm misc and some of the biggest
> drivers.
> ---
>   drivers/gpu/drm/Makefile | 27 +++++++++++++++++++++++++++
>   1 file changed, 27 insertions(+)
> 
> diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> index b4cb0835620a..6939e4ea13d5 100644
> --- a/drivers/gpu/drm/Makefile
> +++ b/drivers/gpu/drm/Makefile
> @@ -5,6 +5,33 @@
>   
>   CFLAGS-$(CONFIG_DRM_USE_DYNAMIC_DEBUG)	+= -DDYNAMIC_DEBUG_MODULE
>   
> +# Unconditionally enable W=1 warnings locally
> +# --- begin copy-paste W=1 warnings from scripts/Makefile.extrawarn
> +subdir-ccflags-y += -Wextra -Wunused -Wno-unused-parameter
> +subdir-ccflags-y += -Wmissing-declarations
> +subdir-ccflags-y += $(call cc-option, -Wrestrict)
> +subdir-ccflags-y += -Wmissing-format-attribute
> +subdir-ccflags-y += -Wmissing-prototypes
> +subdir-ccflags-y += -Wold-style-definition
> +subdir-ccflags-y += -Wmissing-include-dirs
> +subdir-ccflags-y += $(call cc-option, -Wunused-but-set-variable)
> +subdir-ccflags-y += $(call cc-option, -Wunused-const-variable)
> +subdir-ccflags-y += $(call cc-option, -Wpacked-not-aligned)
> +subdir-ccflags-y += $(call cc-option, -Wformat-overflow)
> +subdir-ccflags-y += $(call cc-option, -Wformat-truncation)
> +subdir-ccflags-y += $(call cc-option, -Wstringop-overflow)
> +subdir-ccflags-y += $(call cc-option, -Wstringop-truncation)
> +# The following turn off the warnings enabled by -Wextra
> +ifeq ($(findstring 2, $(KBUILD_EXTRA_WARN)),)
> +subdir-ccflags-y += -Wno-missing-field-initializers
> +subdir-ccflags-y += -Wno-type-limits
> +subdir-ccflags-y += -Wno-shift-negative-value
> +endif
> +ifeq ($(findstring 3, $(KBUILD_EXTRA_WARN)),)
> +subdir-ccflags-y += -Wno-sign-compare
> +endif
> +# --- end copy-paste
> +
>   drm-y := \
>   	drm_aperture.o \
>   	drm_atomic.o \
-- 
Hamza