drm/client: Make client support optional

Only build client code if DRM_CLIENT has been selected. Automatially
do so if one of the default clients has been enabled. If client support
has been disabled, the helpers for client-related events are empty and
the regular client functions are not present.

Amdgpu has an internal DRM client, so it has to select DRM_CLIENT by
itself unconditionally.

v3:
- provide empty drm_client_debugfs_init() if DRM_CLIENT=n (kernel
  test robot)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: Xinhui Pan <Xinhui.Pan@amd.com>
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241014085740.582287-12-tzimmermann@suse.de

drivers/gpu/drm/Kconfig

@@ -210,6 +210,15 @@ config DRM_DEBUG_MODESET_LOCK
 
 	  If in doubt, say "N".
 
+config DRM_CLIENT
+	bool
+	depends on DRM
+	help
+	  Enables support for DRM clients. DRM drivers that need
+	  struct drm_client_dev and its interfaces should select this
+	  option. Drivers that support the default clients should
+	  select DRM_CLIENT_SELECTION instead.
+
 config DRM_CLIENT_SELECTION
 	bool
 	depends on DRM
@@ -225,6 +234,7 @@ config DRM_CLIENT_SETUP
 config DRM_FBDEV_EMULATION
 	bool "Enable legacy fbdev support for your modesetting driver"
 	depends on DRM
+	select DRM_CLIENT
 	select FRAMEBUFFER_CONSOLE_DETECT_PRIMARY if FRAMEBUFFER_CONSOLE
 	default FB
 	help

drivers/gpu/drm/Makefile

@@ -40,9 +40,6 @@ drm-y := \
 	drm_blend.o \
 	drm_bridge.o \
 	drm_cache.o \
-	drm_client.o \
-	drm_client_event.o \
-	drm_client_modeset.o \
 	drm_color_mgmt.o \
 	drm_connector.o \
 	drm_crtc.o \
@@ -76,6 +73,10 @@ drm-y := \
 	drm_vblank_work.o \
 	drm_vma_manager.o \
 	drm_writeback.o
+drm-$(CONFIG_DRM_CLIENT) += \
+	drm_client.o \
+	drm_client_event.o \
+	drm_client_modeset.o
 drm-$(CONFIG_DRM_LIB_RANDOM) += lib/drm_random.o
 drm-$(CONFIG_COMPAT) += drm_ioc32.o
 drm-$(CONFIG_DRM_PANEL) += drm_panel.o

drivers/gpu/drm/amd/amdgpu/Kconfig

@@ -5,6 +5,7 @@ config DRM_AMDGPU
 	depends on DRM && PCI && MMU
 	depends on !UML
 	select FW_LOADER
+	select DRM_CLIENT
 	select DRM_CLIENT_SELECTION
 	select DRM_DISPLAY_DP_HELPER
 	select DRM_DISPLAY_DSC_HELPER

drivers/gpu/drm/drm_client_event.c

@@ -14,6 +14,8 @@
 #include <drm/drm_drv.h>
 #include <drm/drm_print.h>
 
+#include "drm_internal.h"
+
 /**
  * drm_client_dev_unregister - Unregister clients
  * @dev: DRM device

drivers/gpu/drm/drm_debugfs.c

@@ -32,7 +32,6 @@
 #include <drm/drm_atomic.h>
 #include <drm/drm_auth.h>
 #include <drm/drm_bridge.h>
-#include <drm/drm_client.h>
 #include <drm/drm_debugfs.h>
 #include <drm/drm_device.h>
 #include <drm/drm_drv.h>

drivers/gpu/drm/drm_internal.h

@@ -48,6 +48,14 @@ struct drm_prime_file_private;
 struct drm_printer;
 struct drm_vblank_crtc;
 
+/* drm_client_event.c */
+#if defined(CONFIG_DRM_CLIENT)
+void drm_client_debugfs_init(struct drm_device *dev);
+#else
+static inline void drm_client_debugfs_init(struct drm_device *dev)
+{ }
+#endif
+
 /* drm_file.c */
 extern struct mutex drm_global_mutex;
 bool drm_dev_needs_global_mutex(struct drm_device *dev);

include/drm/drm_client.h

@@ -236,6 +236,4 @@ int drm_client_modeset_dpms(struct drm_client_dev *client, int mode);
 	drm_for_each_connector_iter(connector, iter) \
 		if (connector->connector_type != DRM_MODE_CONNECTOR_WRITEBACK)
 
-void drm_client_debugfs_init(struct drm_device *dev);
-
 #endif

include/drm/drm_client_event.h

@@ -5,10 +5,23 @@
 
 struct drm_device;
 
+#if defined(CONFIG_DRM_CLIENT)
 void drm_client_dev_unregister(struct drm_device *dev);
 void drm_client_dev_hotplug(struct drm_device *dev);
 void drm_client_dev_restore(struct drm_device *dev);
 void drm_client_dev_suspend(struct drm_device *dev, bool holds_console_lock);
 void drm_client_dev_resume(struct drm_device *dev, bool holds_console_lock);
+#else
+static inline void drm_client_dev_unregister(struct drm_device *dev)
+{ }
+static inline void drm_client_dev_hotplug(struct drm_device *dev)
+{ }
+static inline void drm_client_dev_restore(struct drm_device *dev)
+{ }
+static inline void drm_client_dev_suspend(struct drm_device *dev, bool holds_console_lock)
+{ }
+static inline void drm_client_dev_resume(struct drm_device *dev, bool holds_console_lock)
+{ }
+#endif
 
 #endif