linux-imx

drm/imx: dpu: crtc: Precisely send vbland event if CRTC is active

If CRTC is active, we should send vblank event in vblank
interrupt handler to make sure it's sent precisely.  This
patch caches the event to be sent at dpu_crtc->event in
the ->atomic_enable() and the ->atomic_flush() callbacks
and finally sends it out in dpu_vbl_irq_handler().  Since
we rely on the interrupt handler to send the event, we
call drm_crtc_vblank_get() to get a vblank refcount to
guarantee the interrupt is enabled when caching the event
in dpu_crtc_queue_state_event() and call drm_crtc_vblank_put()
to drop a vblank refcount in the interrupt handler.

Signed-off-by: Liu Ying <victor.liu@nxp.com>