drm: Add drm_device->fb_helper pointer

drm_fb_helper is *the* way of doing fbdev emulation so add a pointer to
struct drm_device. This makes it possible to add callback helpers for
.last_close and .output_poll_changed further reducing fbdev emulation
footprint in drivers. The pointer is set by drm_fb_helper_init() and
cleared by drm_fb_helper_fini().

Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20171030153951.56269-3-noralf@tronnes.org

drivers/gpu/drm/drm_fb_helper.c

@@ -799,8 +799,10 @@ int drm_fb_helper_init(struct drm_device *dev,
 	struct drm_mode_config *config = &dev->mode_config;
 	int i;
 
-	if (!drm_fbdev_emulation)
+	if (!drm_fbdev_emulation) {
+		dev->fb_helper = fb_helper;
 		return 0;
+	}
 
 	if (!max_conn_count)
 		return -EINVAL;
@@ -835,6 +837,8 @@ int drm_fb_helper_init(struct drm_device *dev,
 		i++;
 	}
 
+	dev->fb_helper = fb_helper;
+
 	return 0;
 out_free:
 	drm_fb_helper_crtc_free(fb_helper);
@@ -913,7 +917,12 @@ void drm_fb_helper_fini(struct drm_fb_helper *fb_helper)
 {
 	struct fb_info *info;
 
-	if (!drm_fbdev_emulation || !fb_helper)
+	if (!fb_helper)
+		return;
+
+	fb_helper->dev->fb_helper = NULL;
+
+	if (!drm_fbdev_emulation)
 		return;
 
 	cancel_work_sync(&fb_helper->resume_work);

include/drm/drm_device.h

@@ -17,6 +17,7 @@ struct drm_vblank_crtc;
 struct drm_sg_mem;
 struct drm_local_map;
 struct drm_vma_offset_manager;
+struct drm_fb_helper;
 
 struct inode;
 
@@ -185,6 +186,14 @@ struct drm_device {
 	struct drm_vma_offset_manager *vma_offset_manager;
 	/*@} */
 	int switch_power_state;
+
+	/**
+	 * @fb_helper:
+	 *
+	 * Pointer to the fbdev emulation structure.
+	 * Set by drm_fb_helper_init() and cleared by drm_fb_helper_fini().
+	 */
+	struct drm_fb_helper *fb_helper;
 };
 
 #endif