Revert "drm/i915: Use atomic commits for legacy page_flips"

This reverts commit ee042aa4.

Something appears to be off in the timing, but as far as I can tell it
is not along the event delivery path. The net effect appears to be
rendering flicker (the current render buffer appears on the scanout,
with what appears to be active rendering for a fraction of a frame) and
is causing me a headache.

The cursor is also being stalled by page flips, causing a "heavy mouse"
and jitter.

Daniel Stone did find what appears to the cause of the tearing, in
https://lists.freedesktop.org/archives/intel-gfx/2016-June/099466.html
That is the parameter passed to intel_atomic_commit_tail is the
old_state but we need the new_state to wait upon.

That leaves the question of how the CRC based tests didn't spot the
error (how can we improve our tests?), the issue of legacy cursor
stalling flips, and the issue of flips stalling the cursor. For the
moment, step back until the condundrum of new/old state is reviewed
along with more tests!
Reported-and-tested-by: Steven Newbury <steve@snewbury.org.uk>
Reported-by: Rafael Ristovski  <rafael.ristovski@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96593
Testcase: igt/kms_cursor_legacy/basic-cursor-vs-flip
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1466772243-21879-1-git-send-email-chris@chris-wilson.co.ukAcked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -11646,7 +11646,6 @@ void intel_check_page_flip(struct drm_i915_private *dev_priv, int pipe)
 	spin_unlock(&dev->event_lock);
 }
 
-__maybe_unused
 static int intel_crtc_page_flip(struct drm_crtc *crtc,
 				struct drm_framebuffer *fb,
 				struct drm_pending_vblank_event *event,
@@ -14008,7 +14007,7 @@ static const struct drm_crtc_funcs intel_crtc_funcs = {
 	.set_config = drm_atomic_helper_set_config,
 	.set_property = drm_atomic_helper_crtc_set_property,
 	.destroy = intel_crtc_destroy,
-	.page_flip = drm_atomic_helper_page_flip,
+	.page_flip = intel_crtc_page_flip,
 	.atomic_duplicate_state = intel_crtc_duplicate_state,
 	.atomic_destroy_state = intel_crtc_destroy_state,
 };