drm/fb_helper: Disable all crtc's when initial setup fails.

Some drivers like i915 start with crtc's enabled, but with deferred
fbcon setup they were no longer disabled as part of fbdev setup.
Headless units could no longer enter pc3 state because the crtc was
still enabled.

Fix this by calling restore_fbdev_mode when we would have called
it otherwise once during initial fbdev setup.
Signed-off-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Fixes: ca91a275 ("drm/fb-helper: Support deferred setup")
Cc: <stable@vger.kernel.org> # v4.14+
Reported-by: NThomas Voegtle <tv@lio96.de>
Tested-by: NThomas Voegtle <tv@lio96.de>
Reviewed-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20171128111603.62757-1-maarten.lankhorst@linux.intel.com

drivers/gpu/drm/drm_fb_helper.c

@@ -1809,6 +1809,10 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
 
 	if (crtc_count == 0 || sizes.fb_width == -1 || sizes.fb_height == -1) {
 		DRM_INFO("Cannot find any crtc or sizes\n");
+
+		/* First time: disable all crtc's.. */
+		if (!fb_helper->deferred_setup && !READ_ONCE(fb_helper->dev->master))
+			restore_fbdev_mode(fb_helper);
 		return -EAGAIN;
 	}