drm/nouveau: Fix nv50_mstc->best_encoder()

As mentioned in the previous commit, we currently prevent new modesets
on recently-removed MST connectors by returning no encoder from our
->best_encoder() callback once the MST port has disappeared. This is
wrong however, because it prevents legacy modesetting users from being
able to disable CRTCs on MST connectors after the connector's respective
topology has disappeared.

So, fix this by instead by just always returning a valid encoder.

Changes since v2:
- Remove usage of atomic MST helper for now, since that got replaced
  with a much simpler solution

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Ben Skeggs <bskeggs@redhat.com>
Cc: stable@vger.kernel.org
Link: https://patchwork.freedesktop.org/patch/msgid/20181008232437.5571-3-lyude@redhat.com

diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
index a9bb656058e524aec4c183bd005ae6ddd1e02588..6d576249618a2c97226866df1827ada29fbe6845 100644 (file)
--- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
@@ -843,22 +843,16 @@ nv50_mstc_atomic_best_encoder(struct drm_connector *connector,
 {
        struct nv50_head *head = nv50_head(connector_state->crtc);
        struct nv50_mstc *mstc = nv50_mstc(connector);
-       if (mstc->port) {
-               struct nv50_mstm *mstm = mstc->mstm;
-               return &mstm->msto[head->base.index]->encoder;
-       }
-       return NULL;
+
+       return &mstc->mstm->msto[head->base.index]->encoder;
 }
 
 static struct drm_encoder *
 nv50_mstc_best_encoder(struct drm_connector *connector)
 {
        struct nv50_mstc *mstc = nv50_mstc(connector);
-       if (mstc->port) {
-               struct nv50_mstm *mstm = mstc->mstm;
-               return &mstm->msto[0]->encoder;
-       }
-       return NULL;
+
+       return &mstc->mstm->msto[0]->encoder;
 }
 
 static enum drm_mode_status