drm: add drm_send_vblank_event() helper (v5)

A helper that drivers can use to send vblank event after a pageflip.
If the driver doesn't support proper vblank irq based time/seqn then
just pass -1 for the pipe # to get do_gettimestamp() behavior (since
there are a lot of drivers that don't use drm_vblank_count_and_time())

Also an internal send_vblank_event() helper for the various other code
paths within drm_irq that also need to send vblank events.

v1: original
v2: add back 'vblwait->reply.sequence = seq' which should not have
    been deleted
v3: add WARN_ON() in case lock is not held and comments
v4: use WARN_ON_SMP() instead to fix issue with !SMP && !DEBUG_SPINLOCK
    as pointed out by Marcin Slusarz
v5: update docbook

Signed-off-by: Rob Clark <rob@ti.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 3fd8280..29eb237 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -1431,6 +1431,8 @@
 extern u32 drm_vblank_count(struct drm_device *dev, int crtc);
 extern u32 drm_vblank_count_and_time(struct drm_device *dev, int crtc,
 				     struct timeval *vblanktime);
+extern void drm_send_vblank_event(struct drm_device *dev, int crtc,
+				     struct drm_pending_vblank_event *e);
 extern bool drm_handle_vblank(struct drm_device *dev, int crtc);
 extern int drm_vblank_get(struct drm_device *dev, int crtc);
 extern void drm_vblank_put(struct drm_device *dev, int crtc);