drm/i915: Ensure plane->state->fb stays in sync with plane->fb

plane->state->fb and plane->fb should always reference the same FB so
that atomic and legacy codepaths have the same view of display state.
In commit

        commit db068420560511de80ac59222644f2bdf278c3d5
        Author: Matt Roper <matthew.d.roper@intel.com>
        Date:   Fri Jan 30 16:22:36 2015 -0800

            drm/i915: Keep plane->state updated on pageflip

we already fixed one case where these two pointers could get out of
sync.  However it turns out there are a few other places (mainly dealing
with initial FB setup at boot) that directly set plane->fb and neglect
to update plane->state->fb.  If we never do a successful update through
the atomic pipeline, the RmFB cleanup code will look at the
plane->state->fb pointer, which has never actually been set to a
legitimate value, and try to clean it up, leading to BUG's.

Add a quick helper function to synchronize plane->state->fb with
plane->fb (and update reference counts accordingly) and call it
everywhere the driver tries to manually set plane->fb outside of the
atomic pipeline.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88909
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -2410,6 +2410,20 @@ out_unref_obj:
 	return false;
 }
 
+/* Update plane->state->fb to match plane->fb after driver-internal updates */
+static void
+update_state_fb(struct drm_plane *plane)
+{
+	if (plane->fb == plane->state->fb)
+		return;
+
+	if (plane->state->fb)
+		drm_framebuffer_unreference(plane->state->fb);
+	plane->state->fb = plane->fb;
+	if (plane->state->fb)
+		drm_framebuffer_reference(plane->state->fb);
+}
+
 static void
 intel_find_plane_obj(struct intel_crtc *intel_crtc,
 		     struct intel_initial_plane_config *plane_config)
@@ -2456,6 +2470,8 @@ intel_find_plane_obj(struct intel_crtc *intel_crtc,
 			break;
 		}
 	}
+
+	update_state_fb(intel_crtc->base.primary);
 }
 
 static void i9xx_update_primary_plane(struct drm_crtc *crtc,
@@ -6635,6 +6651,7 @@ i9xx_get_initial_plane_config(struct intel_crtc *crtc,
 		      plane_config->size);
 
 	crtc->base.primary->fb = fb;
+	update_state_fb(crtc->base.primary);
 }
 
 static void chv_crtc_clock_get(struct intel_crtc *crtc,
@@ -7672,6 +7689,7 @@ skylake_get_initial_plane_config(struct intel_crtc *crtc,
 		      plane_config->size);
 
 	crtc->base.primary->fb = fb;
+	update_state_fb(crtc->base.primary);
 	return;
 
 error:
@@ -7763,6 +7781,7 @@ ironlake_get_initial_plane_config(struct intel_crtc *crtc,
 		      plane_config->size);
 
 	crtc->base.primary->fb = fb;
+	update_state_fb(crtc->base.primary);
 }
 
 static bool ironlake_get_pipe_config(struct intel_crtc *crtc,
@@ -9800,13 +9819,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
 	drm_gem_object_reference(&obj->base);
 
 	crtc->primary->fb = fb;
-
-	/* Keep state structure in sync */
-	if (crtc->primary->state->fb)
-		drm_framebuffer_unreference(crtc->primary->state->fb);
-	crtc->primary->state->fb = fb;
-	if (crtc->primary->state->fb)
-		drm_framebuffer_reference(crtc->primary->state->fb);
+	update_state_fb(crtc->primary);
 
 	work->pending_flip_obj = obj;
 
@@ -9875,6 +9888,7 @@ cleanup_unpin:
 cleanup_pending:
 	atomic_dec(&intel_crtc->unpin_work_count);
 	crtc->primary->fb = old_fb;
+	update_state_fb(crtc->primary);
 	drm_framebuffer_unreference(work->old_fb);
 	drm_gem_object_unreference(&obj->base);
 	mutex_unlock(&dev->struct_mutex);
@@ -13709,6 +13723,7 @@ void intel_modeset_gem_init(struct drm_device *dev)
 				  to_intel_crtc(c)->pipe);
 			drm_framebuffer_unreference(c->primary->fb);
 			c->primary->fb = NULL;
+			update_state_fb(c->primary);
 		}
 	}
 	mutex_unlock(&dev->struct_mutex);