drm/i915: Fixing eDP detection on certain platforms

Since commit 30d9aa4265fe ("drm/i915: Read sink_count dpcd always"),
the status of a DP connector depends on its sink count value.
However, some eDP panels don't set that value appropriately,
causing them to be reported as disconnected.
Fix this by ignoring sink count for eDP.

v2: Rephrased commit message. (Ander)
    In case of eDP, returning status as connected if DPCD
    read succeeds to avoid any further operations.

Fixes: 30d9aa4265fe ("drm/i915: Read sink_count dpcd always")
Cc: Ander Conselvan De Oliveira <conselvan2@gmail.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Reported-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Signed-off-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
Signed-off-by: Shubhangi Shrivastava <shubhangi.shrivastava@intel.com>
Tested-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1460444034-22320-1-git-send-email-shubhangi.shrivastava@intel.com

drivers/gpu/drm/i915/intel_dp.c

@@ -3776,7 +3776,7 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
 	 * downstream port information. So, an early return here saves
 	 * time from performing other operations which are not required.
 	 */
-	if (!intel_dp->sink_count)
+	if (!is_edp(intel_dp) && !intel_dp->sink_count)
 		return false;
 
 	/* Check if the panel supports PSR */
@@ -4309,6 +4309,9 @@ intel_dp_detect_dpcd(struct intel_dp *intel_dp)
 	if (!intel_dp_get_dpcd(intel_dp))
 		return connector_status_disconnected;
 
+	if (is_edp(intel_dp))
+		return connector_status_connected;
+
 	/* if there's no downstream port, we're done */
 	if (!(dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT))
 		return connector_status_connected;