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

[Daniel Vetter]

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 at 
linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
---
 drivers/gpu/drm/drm_atomic_helper.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c 
b/drivers/gpu/drm/drm_atomic_helper.c
index d6d80b30f751..aff616dc6caf 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -86,6 +86,27 @@ 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)
@@ -235,6 +256,13 @@ 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);

-- 
2.5.1