[PATCH v2] drm: ensure drm headers are self-contained and pass kernel-doc

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

Ensure drm headers build, are self-contained, have header guards, and
have no kernel-doc warnings, when CONFIG_DRM_HEADER_TEST=y.

The mechanism follows similar patters used in i915, xe, and usr/include.

To cover include/drm, we need to recurse there using the top level
Kbuild and the new include/Kbuild files.

v2: make DRM_HEADER_TEST depend on DRM

Suggested-by: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
---
 Kbuild                   |  1 +
 drivers/gpu/drm/Kconfig  | 11 +++++++++++
 drivers/gpu/drm/Makefile | 18 ++++++++++++++++++
 include/Kbuild           |  1 +
 include/drm/Makefile     | 18 ++++++++++++++++++
 5 files changed, 49 insertions(+)
 create mode 100644 include/Kbuild
 create mode 100644 include/drm/Makefile

diff --git a/Kbuild b/Kbuild
index 464b34a08f51..f327ca86990c 100644
--- a/Kbuild
+++ b/Kbuild
@@ -97,3 +97,4 @@ obj-$(CONFIG_SAMPLES)	+= samples/
 obj-$(CONFIG_NET)	+= net/
 obj-y			+= virt/
 obj-y			+= $(ARCH_DRIVERS)
+obj-$(CONFIG_DRM_HEADER_TEST)	+= include/
diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 3914aaf443a8..a388c4fda984 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -431,3 +431,14 @@ config DRM_WERROR
 	  this config option is disabled by default.
 
 	  If in doubt, say N.
+
+config DRM_HEADER_TEST
+	bool "Ensure DRM headers are self-contained and pass kernel-doc"
+	depends on DRM && EXPERT
+	default n
+	help
+	  Ensure the DRM subsystem headers both under drivers/gpu/drm and
+	  include/drm compile, are self-contained, have header guards, and have
+	  no kernel-doc warnings.
+
+	  If in doubt, say N.
diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index a73c04d2d7a3..6605d5686d01 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -218,3 +218,21 @@ obj-y			+= solomon/
 obj-$(CONFIG_DRM_SPRD) += sprd/
 obj-$(CONFIG_DRM_LOONGSON) += loongson/
 obj-$(CONFIG_DRM_POWERVR) += imagination/
+
+# Ensure drm headers are self-contained and pass kernel-doc
+hdrtest-files := \
+	$(shell cd $(srctree)/$(src) && find . -maxdepth 1 -name 'drm_*.h') \
+	$(shell cd $(srctree)/$(src) && find display lib -name '*.h')
+
+always-$(CONFIG_DRM_HEADER_TEST) += \
+	$(patsubst %.h,%.hdrtest, $(hdrtest-files))
+
+# Include the header twice to detect missing include guard.
+quiet_cmd_hdrtest = HDRTEST $(patsubst %.hdrtest,%.h,$@)
+      cmd_hdrtest = \
+		$(CC) $(c_flags) -fsyntax-only -x c /dev/null -include $< -include $<; \
+		$(srctree)/scripts/kernel-doc -none $(if $(CONFIG_DRM_WERROR),-Werror) $<; \
+		touch $@
+
+$(obj)/%.hdrtest: $(src)/%.h FORCE
+	$(call if_changed_dep,hdrtest)
diff --git a/include/Kbuild b/include/Kbuild
new file mode 100644
index 000000000000..5e76a599e2dd
--- /dev/null
+++ b/include/Kbuild
@@ -0,0 +1 @@
+obj-$(CONFIG_DRM_HEADER_TEST)	+= drm/
diff --git a/include/drm/Makefile b/include/drm/Makefile
new file mode 100644
index 000000000000..b9f391d7aadd
--- /dev/null
+++ b/include/drm/Makefile
@@ -0,0 +1,18 @@
+# SPDX-License-Identifier: GPL-2.0
+
+# Ensure drm headers are self-contained and pass kernel-doc
+hdrtest-files := \
+	$(shell cd $(srctree)/$(src) && find * -name '*.h' 2>/dev/null)
+
+always-$(CONFIG_DRM_HEADER_TEST) += \
+	$(patsubst %.h,%.hdrtest, $(hdrtest-files))
+
+# Include the header twice to detect missing include guard.
+quiet_cmd_hdrtest = HDRTEST $(patsubst %.hdrtest,%.h,$@)
+      cmd_hdrtest = \
+		$(CC) $(c_flags) -fsyntax-only -x c /dev/null -include $< -include $<; \
+		$(srctree)/scripts/kernel-doc -none $(if $(CONFIG_DRM_WERROR),-Werror) $<; \
+		touch $@
+
+$(obj)/%.hdrtest: $(src)/%.h FORCE
+	$(call if_changed_dep,hdrtest)
-- 
2.39.2