VBlank event handling
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## VBlank event handling

The DRM core exposes two vertical blank related ioctls:

DRM_IOCTL_WAIT_VBLANK

  This takes a struct drm_wait_vblank structure as its argument, and it is used to block or request a signal when a specified vblank event occurs.

DRM_IOCTL_MODESET_CTL

  This should be called by application level drivers before and after mode setting, since on many devices the vertical blank counter is reset at that time. Internally, the DRM snapshots the last vblank count when the ioctl is called with the _DRM_PRE_MODESET command, so that the counter won't go backwards (which is dealt with when _DRM_POST_MODESET is used).

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Chapter 3. Userland interfaces | Home | Appendix A. DRM Driver API