drm/atomic-helper: Reject attempts at re-stealing encoders

This can happen when we run out of encoders for a multi-crtc modeset,
or also when userspace is silly and tries to clone multiple connectors
that need the same encoder on the same crtc.

Reported-and-Tested-and-Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1449136154-11588-1-git-send-email-daniel.vetter@ffwll.ch

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index d9053eb..74a5fc4 100644 (file)
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -80,6 +80,27 @@ drm_atomic_helper_plane_changed(struct drm_atomic_state *state,
        }
 }
 
+static bool
+check_pending_encoder_assignment(struct drm_atomic_state *state,
+                                struct drm_encoder *new_encoder,
+                                struct drm_connector *new_connector)
+{
+       struct drm_connector *connector;
+       struct drm_connector_state *conn_state;
+       int i;
+
+       for_each_connector_in_state(state, connector, conn_state, i) {
+               if (conn_state->best_encoder != new_encoder)
+                       continue;
+
+               /* encoder already assigned and we're trying to re-steal it! */
+               if (connector->state->best_encoder != conn_state->best_encoder)
+                       return false;
+       }
+
+       return true;
+}
+
 static struct drm_crtc *
 get_current_crtc_for_encoder(struct drm_device *dev,
                             struct drm_encoder *encoder)
@@ -229,6 +250,13 @@ update_connector_routing(struct drm_atomic_state *state, int conn_idx)
                return 0;
        }
 
+       if (!check_pending_encoder_assignment(state, new_encoder, connector)) {
+               DRM_DEBUG_ATOMIC("Encoder for [CONNECTOR:%d:%s] already assigned\n",
+                                connector->base.id,
+                                connector->name);
+               return -EINVAL;
+       }
+
        encoder_crtc = get_current_crtc_for_encoder(state->dev,
                                                    new_encoder);