drm: Add drm_plane_force_disable()

drm_plane_force_disable() will forcibly disable the plane even if user
had previously requested the plane to be enabled.

This can be used to force planes to be off when restoring the fbdev
mode.

The code was simply pulled from drm_framebuffer_remove(), which now
calls the new function as well.

v2: Check plane->fb in drm_plane_force_disable(), drop bogus comment
    about disabling crtc

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@gmail.com>

drivers/gpu/drm/drm_crtc.c

@@ -592,16 +592,8 @@ void drm_framebuffer_remove(struct drm_framebuffer *fb)
 		}
 
 		list_for_each_entry(plane, &dev->mode_config.plane_list, head) {
-			if (plane->fb == fb) {
-				/* should turn off the crtc */
-				ret = plane->funcs->disable_plane(plane);
-				if (ret)
-					DRM_ERROR("failed to disable plane with busy fb\n");
-				/* disconnect the plane from the fb and crtc: */
-				__drm_framebuffer_unreference(plane->fb);
-				plane->fb = NULL;
-				plane->crtc = NULL;
-			}
+			if (plane->fb == fb)
+				drm_plane_force_disable(plane);
 		}
 		drm_modeset_unlock_all(dev);
 	}
@@ -891,6 +883,23 @@ void drm_plane_cleanup(struct drm_plane *plane)
 }
 EXPORT_SYMBOL(drm_plane_cleanup);
 
+void drm_plane_force_disable(struct drm_plane *plane)
+{
+	int ret;
+
+	if (!plane->fb)
+		return;
+
+	ret = plane->funcs->disable_plane(plane);
+	if (ret)
+		DRM_ERROR("failed to disable plane with busy fb\n");
+	/* disconnect the plane from the fb and crtc: */
+	__drm_framebuffer_unreference(plane->fb);
+	plane->fb = NULL;
+	plane->crtc = NULL;
+}
+EXPORT_SYMBOL(drm_plane_force_disable);
+
 /**
  * drm_mode_create - create a new display mode
  * @dev: DRM device

include/drm/drm_crtc.h

@@ -894,6 +894,7 @@ extern int drm_plane_init(struct drm_device *dev,
 			  const uint32_t *formats, uint32_t format_count,
 			  bool priv);
 extern void drm_plane_cleanup(struct drm_plane *plane);
+extern void drm_plane_force_disable(struct drm_plane *plane);
 
 extern void drm_encoder_cleanup(struct drm_encoder *encoder);