drm/i915/crt: Do not rely upon the HPD presence pin

Whilst most monitors do wire up the HPD presence pin, it seems quite a
few KVM do not. Therefore if we simply rely on the HPD pin being
asserted to indicate a connected monitor we fail miserable, so fall back
to performing a DCC query for the EDID.

Reported-and-tested-by: Matthieu LAVIE <boiteamadmax@hotmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=50501
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_crt.c

@@ -453,13 +453,15 @@ intel_crt_detect(struct drm_connector *connector, bool force)
 	struct intel_load_detect_pipe tmp;
 
 	if (I915_HAS_HOTPLUG(dev)) {
+		/* We can not rely on the HPD pin always being correctly wired
+		 * up, for example many KVM do not pass it through, and so
+		 * only trust an assertion that the monitor is connected.
+		 */
 		if (intel_crt_detect_hotplug(connector)) {
 			DRM_DEBUG_KMS("CRT detected via hotplug\n");
 			return connector_status_connected;
-		} else {
+		} else
 			DRM_DEBUG_KMS("CRT not detected via hotplug\n");
-			return connector_status_disconnected;
-		}
 	}
 
 	if (intel_crt_detect_ddc(connector))