drm/i915/ddi: fix intel_display_port_aux_power_domain() after HDMI detect

Due to the current sharing of the DDI encoder between DP and HDMI
connectors we can run the DP detection after the HDMI detection has
already set the shared encoder's type. For now solve this keeping the
current behavior and running the detection in this case too. For a proper
solution Ville suggested to split the encoder into an HDMI and DP one, that
can be done as a follow-up.

This issue triggers the WARN in intel_display_port_aux_power_domain() and
was introduced in:
commit 25f78f58e5
Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
Date:   Mon Nov 16 15:01:04 2015 +0100

    drm/i915: Clean up AUX power domain handling

CC: Patrik Jakobsson <patrik.jakobsson@linux.intel.com>
CC: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Patrik Jakobsson <patrik.jakobsson@linux.intel.com>
[Cherry-picked from drm-intel-next-queued 651174a4 (Imre)]
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1448643329-18675-4-git-send-email-imre.deak@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -5258,7 +5258,14 @@ intel_display_port_aux_power_domain(struct intel_encoder *intel_encoder)
 
 	switch (intel_encoder->type) {
 	case INTEL_OUTPUT_UNKNOWN:
-		/* Only DDI platforms should ever use this output type */
+	case INTEL_OUTPUT_HDMI:
+		/*
+		 * Only DDI platforms should ever use these output types.
+		 * We can get here after the HDMI detect code has already set
+		 * the type of the shared encoder. Since we can't be sure
+		 * what's the status of the given connectors, play safe and
+		 * run the DP detection too.
+		 */
 		WARN_ON_ONCE(!HAS_DDI(dev));
 	case INTEL_OUTPUT_DISPLAYPORT:
 	case INTEL_OUTPUT_EDP: