drm/i915: Use the first mode if there is no preferred mode in the EDID

This matches the algorithm used by earlier kernels when selecting the
mode for the fbcon. And only if there is no modes at all, do we fall
back to using the BIOS configuration. Seamless transition is still
preserved (from the BIOS configuration to ours) so long as the BIOS has
also chosen what we hope is the native configuration.
Reported-by: Knut Petersen <Knut_Petersen@t-online.de>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=78655Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Tested-by: Knut Petersen <Knut_Petersen@t-online.de>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
[Jani: applied Chris' "Please imagine that I wrote this correctly."]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_fbdev.c

@@ -387,6 +387,15 @@ static bool intel_fb_initial_config(struct drm_fb_helper *fb_helper,
 							  height);
 		}
 
+		/* No preferred mode marked by the EDID? Are there any modes? */
+		if (!modes[i] && !list_empty(&connector->modes)) {
+			DRM_DEBUG_KMS("using first mode listed on connector %s\n",
+				      drm_get_connector_name(connector));
+			modes[i] = list_first_entry(&connector->modes,
+						    struct drm_display_mode,
+						    head);
+		}
+
 		/* last resort: use current mode */
 		if (!modes[i]) {
 			/*