drm/i915: Fake HDMI live status

This patch does the following:
- Fakes live status of HDMI as connected (even if that's not).
  While testing certain (monitor + cable) combinations with
  various intel  platforms, it seems that live status register
  doesn't work reliably on some older devices. So limit the
  live_status check for HDMI detection, only for platforms
  from gen7 onwards.

V2: restrict faking live_status to certain platforms
V3: (Ville)
   - keep the debug message for !live_status case
   - fix indentation of comment
   - remove "warning" from the debug message

    (Jani)
   - Change format of fix details in the commit message

Fixes: 237ed86c ("drm/i915: Check live status before reading edid")
Cc: stable@vger.kernel.org # v4.4
Suggested-by: Ville Syrjala <ville.syrjala@linux.intel.com>
Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1461237606-16491-1-git-send-email-shashank.sharma@intel.comSigned-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

drivers/gpu/drm/i915/intel_hdmi.c

@@ -1412,8 +1412,16 @@ intel_hdmi_detect(struct drm_connector *connector, bool force)
 				hdmi_to_dig_port(intel_hdmi));
 	}
 
-	if (!live_status)
-		DRM_DEBUG_KMS("Live status not up!");
+	if (!live_status) {
+		DRM_DEBUG_KMS("HDMI live status down\n");
+		/*
+		 * Live status register is not reliable on all intel platforms.
+		 * So consider live_status only for certain platforms, for
+		 * others, read EDID to determine presence of sink.
+		 */
+		if (INTEL_INFO(dev_priv)->gen < 7 || IS_IVYBRIDGE(dev_priv))
+			live_status = true;
+	}
 
 	intel_hdmi_unset_edid(connector);