drm/nv50: prevent accidently turning off encoders we're actually using

On most cards the DisplayPort connector is created with 2 encoders sharing
a single SOR (for native DP, and for DVI-over-DP).  The previous logic
for turning off unused encoders didn't take into account that we could
have multiple drm_encoders on a single hw encoder and ended up turning off
encoders that were actually being used still.

This patch fixes that issue.  We probably want to look at something a bit
better later on, and only expose one drm_encoder per hw encoder block.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nv50_crtc.c

@@ -432,6 +432,7 @@ nv50_crtc_prepare(struct drm_crtc *crtc)
 	struct nouveau_crtc *nv_crtc = nouveau_crtc(crtc);
 	struct drm_device *dev = crtc->dev;
 	struct drm_encoder *encoder;
+	uint32_t dac = 0, sor = 0;
 
 	NV_DEBUG_KMS(dev, "index %d\n", nv_crtc->index);
 
@@ -439,9 +440,28 @@ nv50_crtc_prepare(struct drm_crtc *crtc)
 	list_for_each_entry(encoder, &dev->mode_config.encoder_list, head) {
 		struct nouveau_encoder *nv_encoder = nouveau_encoder(encoder);
 
-		if (drm_helper_encoder_in_use(encoder))
+		if (!drm_helper_encoder_in_use(encoder))
 			continue;
 
+		if (nv_encoder->dcb->type == OUTPUT_ANALOG ||
+		    nv_encoder->dcb->type == OUTPUT_TV)
+			dac |= (1 << nv_encoder->or);
+		else
+			sor |= (1 << nv_encoder->or);
+	}
+
+	list_for_each_entry(encoder, &dev->mode_config.encoder_list, head) {
+		struct nouveau_encoder *nv_encoder = nouveau_encoder(encoder);
+
+		if (nv_encoder->dcb->type == OUTPUT_ANALOG ||
+		    nv_encoder->dcb->type == OUTPUT_TV) {
+			if (dac & (1 << nv_encoder->or))
+				continue;
+		} else {
+			if (sor & (1 << nv_encoder->or))
+				continue;
+		}
+
 		nv_encoder->disconnect(nv_encoder);
 	}