drm/i915: Interlaced DP output doesn't work on VLV/CHV

Reject interlaced modes on VLV/CHV DP outputs. This simply does
not work correctly in the hardware. We do get some output, but
it's quite corrupted.

The available documentation fails to mention this fact. I
contacted some hardware people who eventually managed to locate
the relevant HSD for VLV, which was resolved by declaring
interlaced DP output as not supported. The HSD was never cloned
for CHV even though it inherited most of the hardware and
thus has the same problems with interlaced DP output.

Cc: Dennis Vshivkov <awesome.walrus+bugzilla@gmail.com>
Reported-by: Dennis Vshivkov <awesome.walrus+bugzilla@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103922
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171129180847.30613-1-ville.syrjala@linux.intel.com
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/i915/intel_dp.c

@@ -1677,6 +1677,10 @@ intel_dp_compute_config(struct intel_encoder *encoder,
 						conn_state->scaling_mode);
 	}
 
+	if ((IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv)) &&
+	    adjusted_mode->flags & DRM_MODE_FLAG_INTERLACE)
+		return false;
+
 	if (adjusted_mode->flags & DRM_MODE_FLAG_DBLCLK)
 		return false;
 
@@ -6093,7 +6097,8 @@ intel_dp_init_connector(struct intel_digital_port *intel_dig_port,
 	drm_connector_init(dev, connector, &intel_dp_connector_funcs, type);
 	drm_connector_helper_add(connector, &intel_dp_connector_helper_funcs);
 
-	connector->interlace_allowed = true;
+	if (!IS_VALLEYVIEW(dev_priv) && !IS_CHERRYVIEW(dev_priv))
+		connector->interlace_allowed = true;
 	connector->doublescan_allowed = 0;
 
 	intel_dp_init_connector_port_info(intel_dig_port);