drm: Provide platform module-init macro

Provide a helper macro to register platform DRM drivers. The new
macro behaves like module_platform_driver() with an additional
test if DRM modesetting has been enabled.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20211222082831.196562-7-javierm@redhat.com

include/drm/drm_module.h

@@ -4,6 +4,7 @@
 #define DRM_MODULE_H
 
 #include <linux/pci.h>
+#include <linux/platform_device.h>
 
 #include <drm/drm_drv.h>
 
@@ -92,4 +93,33 @@ drm_pci_unregister_driver_if_modeset(struct pci_driver *pci_drv, int modeset)
 	module_driver(__pci_drv, drm_pci_register_driver_if_modeset, \
 		      drm_pci_unregister_driver_if_modeset, __modeset)
 
+/*
+ * Platform drivers
+ */
+
+static inline int __init
+drm_platform_driver_register(struct platform_driver *platform_drv)
+{
+	if (drm_firmware_drivers_only())
+		return -ENODEV;
+
+	return platform_driver_register(platform_drv);
+}
+
+/**
+ * drm_module_platform_driver - Register a DRM driver for platform devices
+ * @__platform_drv: the platform driver structure
+ *
+ * Registers a DRM driver for devices on the platform bus. The helper
+ * macro behaves like module_platform_driver() but tests the state of
+ * drm_firmware_drivers_only(). For more complex module initialization,
+ * use module_init() and module_exit() directly.
+ *
+ * Each module may only use this macro once. Calling it replaces
+ * module_init() and module_exit().
+ */
+#define drm_module_platform_driver(__platform_drv) \
+	module_driver(__platform_drv, drm_platform_driver_register, \
+		      platform_driver_unregister)
+
 #endif