drm/omap: protect omap_crtc's event with event_lock spinlock

The vblank_cb callback and the page_flip ioctl can occur together in different
CPU contexts. vblank_cb uses takes tje drm device's event_lock spinlock when
sending the vblank event and updating omap_crtc->event and omap_crtc->od_fb.

Use the same spinlock in page_flip, to make sure the above omap_crtc parameters
are configured sequentially.
Signed-off-by: Archit Taneja <archit@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/gpu/drm/omapdrm/omap_crtc.c

@@ -350,11 +350,15 @@ static int omap_crtc_page_flip_locked(struct drm_crtc *crtc,
 	struct omap_crtc *omap_crtc = to_omap_crtc(crtc);
 	struct drm_plane *primary = crtc->primary;
 	struct drm_gem_object *bo;
+	unsigned long flags;
 
 	DBG("%d -> %d (event=%p)", primary->fb ? primary->fb->base.id : -1,
 			fb->base.id, event);
 
+	spin_lock_irqsave(&dev->event_lock, flags);
+
 	if (omap_crtc->old_fb) {
+		spin_unlock_irqrestore(&dev->event_lock, flags);
 		dev_err(dev->dev, "already a pending flip\n");
 		return -EINVAL;
 	}
@@ -362,6 +366,8 @@ static int omap_crtc_page_flip_locked(struct drm_crtc *crtc,
 	omap_crtc->event = event;
 	omap_crtc->old_fb = primary->fb = fb;
 
+	spin_unlock_irqrestore(&dev->event_lock, flags);
+
 	/*
 	 * Hold a reference temporarily until the crtc is updated
 	 * and takes the reference to the bo.  This avoids it