drm/nv50-/kms: allow disabling of gpu scaling on fixed panels

The hilarious part is that, under X, this won't work anyway because the
server decides to construct its own modes for some reason.

Tested with modetest, which isn't quite as insane.  I'd hope that
wayland is more sensible.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_connector.c

@@ -458,6 +458,28 @@ nouveau_connector_set_property(struct drm_connector *connector,
 
 		switch (value) {
 		case DRM_MODE_SCALE_NONE:
+			/* We allow 'None' for EDID modes, even on a fixed
+			 * panel (some exist with support for lower refresh
+			 * rates, which people might want to use for power
+			 * saving purposes).
+			 *
+			 * Non-EDID modes will force the use of GPU scaling
+			 * to the native mode regardless of this setting.
+			 */
+			switch (nv_connector->type) {
+			case DCB_CONNECTOR_LVDS:
+			case DCB_CONNECTOR_LVDS_SPWG:
+			case DCB_CONNECTOR_eDP:
+				/* ... except prior to G80, where the code
+				 * doesn't support such things.
+				 */
+				if (disp->disp.oclass < NV50_DISP)
+					return -EINVAL;
+				break;
+			default:
+				break;
+			}
+			break;
 		case DRM_MODE_SCALE_FULLSCREEN:
 		case DRM_MODE_SCALE_CENTER:
 		case DRM_MODE_SCALE_ASPECT:
@@ -466,11 +488,6 @@ nouveau_connector_set_property(struct drm_connector *connector,
 			return -EINVAL;
 		}
 
-		/* LVDS always needs gpu scaling */
-		if (connector->connector_type == DRM_MODE_CONNECTOR_LVDS &&
-		    value == DRM_MODE_SCALE_NONE)
-			return -EINVAL;
-
 		/* Changing between GPU and panel scaling requires a full
 		 * modeset
 		 */
@@ -662,8 +679,6 @@ nouveau_connector_scaler_modes_add(struct drm_connector *connector)
 			if (!m)
 				continue;
 
-			m->type |= DRM_MODE_TYPE_DRIVER;
-
 			drm_mode_probed_add(connector, m);
 			modes++;
 		}

drivers/gpu/drm/nouveau/nouveau_connector.h

@@ -72,6 +72,7 @@ struct nouveau_connector {
 	int dithering_mode;
 	int dithering_depth;
 	int scaling_mode;
+	bool scaling_full;
 	enum nouveau_underscan_type underscan;
 	u32 underscan_hborder;
 	u32 underscan_vborder;

drivers/gpu/drm/nouveau/nv50_display.c

@@ -729,8 +729,11 @@ nv50_crtc_set_scale(struct nouveau_crtc *nv_crtc, bool update)
 	 * effectively handles NONE/FULL scaling
 	 */
 	nv_connector = nouveau_crtc_connector_get(nv_crtc);
-	if (nv_connector && nv_connector->native_mode)
+	if (nv_connector && nv_connector->native_mode) {
 		mode = nv_connector->scaling_mode;
+		if (nv_connector->scaling_full) /* non-EDID LVDS/eDP mode */
+			mode = DRM_MODE_SCALE_FULLSCREEN;
+	}
 
 	if (mode != DRM_MODE_SCALE_NONE)
 		omode = nv_connector->native_mode;
@@ -1478,8 +1481,23 @@ nv50_encoder_mode_fixup(struct drm_encoder *encoder,
 
 	nv_connector = nouveau_encoder_connector_get(nv_encoder);
 	if (nv_connector && nv_connector->native_mode) {
-		if (nv_connector->scaling_mode != DRM_MODE_SCALE_NONE)
-			drm_mode_copy(adjusted_mode, nv_connector->native_mode);
+		nv_connector->scaling_full = false;
+		if (nv_connector->scaling_mode == DRM_MODE_SCALE_NONE) {
+			switch (nv_connector->type) {
+			case DCB_CONNECTOR_LVDS:
+			case DCB_CONNECTOR_LVDS_SPWG:
+			case DCB_CONNECTOR_eDP:
+				/* force use of scaler for non-edid modes */
+				if (adjusted_mode->type & DRM_MODE_TYPE_DRIVER)
+					return true;
+				nv_connector->scaling_full = true;
+				break;
+			default:
+				return true;
+			}
+		}
+
+		drm_mode_copy(adjusted_mode, nv_connector->native_mode);
 	}
 
 	return true;