[PATCH v2 4/5] drm/tegra: Implement VBLANK support

[Terje Bergström]

On 22.01.2013 21:59, Mario Kleiner wrote:
> The current swap scheduling is based on having an accurate software 
> vblank counter. Atm. that counter is maintained in software, incremented 
> during vblank irq. At irq off -> on transition we need a hw counter to 
> reinitialize. And there is a timeout between dropping the last reference 
> to a counter via drm_vblank_put() and actually disabling the vblank irq. 
> If the timeout is long enough and a timing sensitive app is aware that 
> vblank counters may be inaccurate/unreliable over long time periods, it 
> can work around the problem.

We have a hardware counter that can be used as VBLANK counter - host1x
sync point register numbers 26 and 27. tegradrm already sets them up in
dc init (DC_CMD_CONT_SYNCPT_VSYNC). Basic syncpt support (read, wait) is
part of my patch set to implement 2D acceleration.

Terje