drm/i915: take a power domain reference while checking the HDMI live status

There are platforms that don't need the full GMBUS power domain (BXT)
while others do (PCH, VLV/CHV). For optimizing this we would need to add
a new power domain, but it's not clear how much we would benefit given
the short time we hold the reference. So for now let's keep things
simple.

v2:
- fix commit message, PCH won't take any redundant power resource after
this change (Ville)
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
[fix commit message in v2 (Imre)]
Link: http://patchwork.freedesktop.org/patch/msgid/1447959301-1263-2-git-send-email-imre.deak@intel.com

drivers/gpu/drm/i915/intel_hdmi.c

@@ -1393,6 +1393,8 @@ intel_hdmi_detect(struct drm_connector *connector, bool force)
 	DRM_DEBUG_KMS("[CONNECTOR:%d:%s]\n",
 		      connector->base.id, connector->name);
 
+	intel_display_power_get(dev_priv, POWER_DOMAIN_GMBUS);
+
 	while (!live_status && --retry) {
 		live_status = intel_digital_port_connected(dev_priv,
 				hdmi_to_dig_port(intel_hdmi));
@@ -1412,6 +1414,8 @@ intel_hdmi_detect(struct drm_connector *connector, bool force)
 	} else
 		status = connector_status_disconnected;
 
+	intel_display_power_put(dev_priv, POWER_DOMAIN_GMBUS);
+
 	return status;
 }