[PATCH 2/7] drm/vc4: Fix vblank handling

[Eric Anholt]

Boris Brezillon <boris.brezillon at free-electrons.com> writes:

> There are two problems related to VBLANK handling in the current CRTC
> driver:
>
> * VBLANK events are missed when the CRTC is being disabled because the
>   driver does not wait till the end of the frame before stopping the
>   HVS and PV blocks. In this case, we should explicitly issue a VBLANK
>   event if there's one waiting
> * when we are enabling a CRTC, drm_crtc_vblank_get() is called before
>   drm_crtc_vblank_on(), which is not supposed to happen (hence the
>   WARN_ON() in the code). To solve the problem, we delay the 'update
>   display list' operation after the CRTC is actually enabled.

Does drm_crtc_vblank_get() actually fail when drm_crtc_vblank_on()
hasn't been called?  The code is a bit twisty, but it looked like we
would track the get refcount and then turn on the interrupt once
drm_crtc_vblank_on() was called.

The first change of the two seems straightforward and good, though (and
possible to separate, right?).
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