drm_vblank_pre_modeset — account for vblanks across mode sets
void drm_vblank_pre_modeset ( | struct drm_device * dev, |
int crtc); |
Account for vblank events across mode setting events, which will likely reset the hardware frame counter.
This is done by grabbing a temporary vblank reference to ensure that the vblank interrupt keeps running across the modeset sequence. With this the software-side vblank frame counting will ensure that there are no jumps or discontinuities.
Unfortunately this approach is racy and also doesn't work when the vblank
interrupt stops running, e.g. across system suspend resume. It is therefore
highly recommended that drivers use the newer drm_vblank_off and
drm_vblank_on instead. drm_vblank_pre_modeset only works correctly when
using “cooked” software vblank frame counters and not relying on any hardware
counters.
Drivers must call drm_vblank_post_modeset when re-enabling the same crtc
again.