drm/arc: Actually bother with handling atomic events.

The drm core has a nice ready-made helper for exactly the simple case
where it should fire on the next vblank.

Note that arming the vblank event in _begin is probably too early, and
might easily result in the vblank firing too early, before the new set
of planes are actually disabled. But that's kinda a minor issue
compared to just outright hanging userspace.

v2: Be more robust and either arm, when the CRTC is on, or just send
the event out right away.

v3: Just unconditionally send out the event directly, for safety -
arcpgu doesn't even have vblank support ...

Cc: Carlos Palminha <palminha@synopsys.com>
Cc: Alexey Brodkin <abrodkin@synopsys.com>
Cc: linux-snps-arc@lists.infradead.org
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1465388359-8070-3-git-send-email-daniel.vetter@ffwll.ch
Link: http://patchwork.freedesktop.org/patch/msgid/1465388359-8070-4-git-send-email-daniel.vetter@ffwll.ch

drivers/gpu/drm/arc/arcpgu_crtc.c

@@ -145,16 +145,14 @@ static int arc_pgu_crtc_atomic_check(struct drm_crtc *crtc,
 static void arc_pgu_crtc_atomic_begin(struct drm_crtc *crtc,
 				      struct drm_crtc_state *state)
 {
-	struct arcpgu_drm_private *arcpgu = crtc_to_arcpgu_priv(crtc);
-	unsigned long flags;
-
-	if (crtc->state->event) {
 	struct drm_pending_vblank_event *event = crtc->state->event;
 
+	if (event) {
 		crtc->state->event = NULL;
-		event->pipe = drm_crtc_index(crtc);
 
-		WARN_ON(drm_crtc_vblank_get(crtc) != 0);
+		spin_lock_irq(&crtc->dev->event_lock);
+		drm_crtc_send_vblank_event(crtc, event);
+		spin_unlock_irq(&crtc->dev->event_lock);
 	}
 }