[RESEND v3 2/2] drm: Add CONFIG_DRM_WERROR

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

Add kconfig to enable -Werror subsystem wide. This is useful for
development and CI to keep the subsystem warning free, while avoiding
issues outside of the subsystem that kernel wide CONFIG_WERROR=y might
hit.

v2: Don't depend on COMPILE_TEST

Reviewed-by: Hamza Mahfooz <hamza.mahfooz@amd.com> # v1
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
---
 drivers/gpu/drm/Kconfig  | 13 +++++++++++++
 drivers/gpu/drm/Makefile |  3 +++
 2 files changed, 16 insertions(+)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 6e853acf15da..c08e18108c2a 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -416,3 +416,16 @@ config DRM_LIB_RANDOM
 config DRM_PRIVACY_SCREEN
 	bool
 	default n
+
+config DRM_WERROR
+	bool "Compile the drm subsystem with warnings as errors"
+	depends on EXPERT
+	default n
+	help
+	  A kernel build should not cause any compiler warnings, and this
+	  enables the '-Werror' flag to enforce that rule in the drm subsystem.
+
+	  The drm subsystem enables more warnings than the kernel default, so
+	  this config option is disabled by default.
+
+	  If in doubt, say N.
diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index ea456f057e8a..a73c04d2d7a3 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -30,6 +30,9 @@ subdir-ccflags-y += -Wno-sign-compare
 endif
 # --- end copy-paste
 
+# Enable -Werror in CI and development
+subdir-ccflags-$(CONFIG_DRM_WERROR) += -Werror
+
 drm-y := \
 	drm_aperture.o \
 	drm_atomic.o \
-- 
2.39.2