drm/i915: Allow DP to work w/o EDID

Allow returning "connected" or "unknown" connector status for DP branch
devices that don't have an EDID. Currently we'd claim the thing as
"disconnected" if there is no EDID.

This stuff used to broken already, I think, but it got more broken by
commit f21a219 ("drm/i915: Splitting intel_dp_detect")

Cc: Damien Cassou <damien@cassou.me>
Cc: freedesktop.org@gp.mailgun.org
Cc: Arno <blouin.arno@gmail.com>
Cc: Shubhangi Shrivastava <shubhangi.shrivastava@intel.com>
Cc: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
Cc: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Cc: stable@vger.kernel.org
Tested-by: Arno <blouin.arno@gmail.com>
Fixes: f21a219 ("drm/i915: Splitting intel_dp_detect")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=83348
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1475481316-8194-2-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>

drivers/gpu/drm/i915/intel_dp.c

@@ -4333,7 +4333,7 @@ intel_dp_unset_edid(struct intel_dp *intel_dp)
 	intel_dp->has_audio = false;
 }
 
-static void
+static enum drm_connector_status
 intel_dp_long_pulse(struct intel_connector *intel_connector)
 {
 	struct drm_connector *connector = &intel_connector->base;
@@ -4357,7 +4357,7 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
 	else
 		status = connector_status_disconnected;
 
-	if (status != connector_status_connected) {
+	if (status == connector_status_disconnected) {
 		intel_dp->compliance_test_active = 0;
 		intel_dp->compliance_test_type = 0;
 		intel_dp->compliance_test_data = 0;
@@ -4419,8 +4419,8 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
 	intel_dp->aux.i2c_defer_count = 0;
 
 	intel_dp_set_edid(intel_dp);
-
-	status = connector_status_connected;
+	if (is_edp(intel_dp) || intel_connector->detect_edid)
+		status = connector_status_connected;
 	intel_dp->detect_done = true;
 
 	/* Try to read the source of the interrupt */
@@ -4439,12 +4439,11 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
 	}
 
 out:
-	if ((status != connector_status_connected) &&
-	    (intel_dp->is_mst == false))
+	if (status != connector_status_connected && !intel_dp->is_mst)
 		intel_dp_unset_edid(intel_dp);
 
 	intel_display_power_put(to_i915(dev), power_domain);
-	return;
+	return status;
 }
 
 static enum drm_connector_status
@@ -4453,7 +4452,7 @@ intel_dp_detect(struct drm_connector *connector, bool force)
 	struct intel_dp *intel_dp = intel_attached_dp(connector);
 	struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
 	struct intel_encoder *intel_encoder = &intel_dig_port->base;
-	struct intel_connector *intel_connector = to_intel_connector(connector);
+	enum drm_connector_status status = connector->status;
 
 	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n",
 		      connector->base.id, connector->name);
@@ -4468,14 +4467,11 @@ intel_dp_detect(struct drm_connector *connector, bool force)
 
 	/* If full detect is not performed yet, do a full detect */
 	if (!intel_dp->detect_done)
-		intel_dp_long_pulse(intel_dp->attached_connector);
+		status = intel_dp_long_pulse(intel_dp->attached_connector);
 
 	intel_dp->detect_done = false;
 
-	if (is_edp(intel_dp) || intel_connector->detect_edid)
-		return connector_status_connected;
-	else
-		return connector_status_disconnected;
+	return status;
 }
 
 static void