There was a potential to crash in the following case:
[   49.985270] [drm:update_connector_routing] Updating routing for 
[CONNECTOR:48:DP-3]
[   49.985273] [drm:update_connector_routing] [CONNECTOR:48:DP-3] keeps 
[ENCODER:33:DP MST-33], now on [CRTC:21:crtc-0]
[   49.985275] [drm:update_connector_routing] Updating routing for 
[CONNECTOR:51:DP-4]
[   49.985278] [drm:steal_encoder] [ENCODER:33:DP MST-33] in use on 
[CRTC:21:crtc-0], stealing it
[   49.985281] [drm:update_connector_routing] [CONNECTOR:51:DP-4] using 
[ENCODER:33:DP MST-33] on [CRTC:21:crtc-0]

This case is not allowed, similar to the previous case of 2 connectors newly 
assigned to the same encoder.

Signed-off-by: Maarten Lankhorst <maarten.lankho...@linux.intel.com>
---
 drivers/gpu/drm/drm_atomic_helper.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c 
b/drivers/gpu/drm/drm_atomic_helper.c
index fc1c06b1d8bb..fa708559542c 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -88,18 +88,18 @@ 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_encoder *new_encoder,
+                                int conn_idx)
 {
        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;
+               if (i >= conn_idx)
+                       break;
 
-               /* encoder already assigned and we're trying to re-steal it! */
-               if (connector->state->best_encoder != conn_state->best_encoder)
+               if (conn_state->best_encoder == new_encoder)
                        return false;
        }
 
@@ -272,7 +272,7 @@ update_connector_routing(struct drm_atomic_state *state,
                return 0;
        }
 
-       if (!check_pending_encoder_assignment(state, new_encoder)) {
+       if (!check_pending_encoder_assignment(state, new_encoder, conn_idx)) {
                DRM_DEBUG_ATOMIC("Encoder for [CONNECTOR:%d:%s] already 
assigned\n",
                                 connector->base.id,
                                 connector->name);
-- 
2.1.0

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