drm/atomic-helper: Do not call ->mode_fixup for CRTC which will be disabled

When a CRTC is going to be disabled, it's state may contain a display mode
with zeroed content.  This could be reproduced by HDMI cable hotplug out
operation with legacy fbdev support in dual display cases.  It would confuse
driver's CRTC callback ->mode_fixup and make the total state be rejected.
So, let's don't call the callback for the CRTC.

Signed-off-by: Liu Ying <gnuiyl@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1464341754-7087-1-git-send-email-gnuiyl@gmail.com

drivers/gpu/drm/drm_atomic_helper.c

@@ -414,6 +414,9 @@ mode_fixup(struct drm_atomic_state *state)
 	for_each_crtc_in_state(state, crtc, crtc_state, i) {
 		const struct drm_crtc_helper_funcs *funcs;
 
+		if (!crtc_state->enable)
+			continue;
+
 		if (!crtc_state->mode_changed &&
 		    !crtc_state->connectors_changed)
 			continue;