[PATCH v2 5/8] drm/atomic: Call drm_atomic_helper_fake_vblank() from the generic commit_tail() helpers

[Boris Brezillon]

On Mon, 2 Jul 2018 09:54:32 +0200
Daniel Vetter <daniel at ffwll.ch> wrote:

> On Fri, Jun 29, 2018 at 01:17:18PM +0200, Boris Brezillon wrote:
> > Now that we have a way to fake VBLANK events when requested by the CRTC
> > hook it up to the generic commit_tail() helpers.
> > 
> > Signed-off-by: Boris Brezillon <boris.brezillon at bootlin.com>  
> 
> I really don't like this. We've had epic amounts of bugs with atomic
> drivers failing to send out vblank events when they should, and I added a
> bunch of debug checks to make sure that doesn't happen anymore.
> 
> Now there's no way anymore for drivers to spot this until they have
> misrenderings on wayland and no idea why. Imo this should only be used by
> specific drivers, with a comment why exactly they need it.

Hm, that's not entirely true. Drivers have to explicitly set
->no_vblank to true for drm_atomic_helper_fake_vblank() to actually do
something, and I seriously hope drivers won't set that field randomly.
So, on all existing drivers but VC4 after the TXP patch, the behavior
will be unchanged, and the core will spot misbehaving drivers just like
before.

> -Daniel
> 
> > ---
> >  drivers/gpu/drm/drm_atomic_helper.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > index ca586993c2a2..1a088462bc42 100644
> > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > @@ -1448,6 +1448,8 @@ void drm_atomic_helper_commit_tail(struct drm_atomic_state *old_state)
> >  
> >  	drm_atomic_helper_commit_modeset_enables(dev, old_state);
> >  
> > +	drm_atomic_helper_fake_vblank(old_state);
> > +
> >  	drm_atomic_helper_commit_hw_done(old_state);
> >  
> >  	drm_atomic_helper_wait_for_vblanks(dev, old_state);
> > @@ -1477,6 +1479,8 @@ void drm_atomic_helper_commit_tail_rpm(struct drm_atomic_state *old_state)
> >  	drm_atomic_helper_commit_planes(dev, old_state,
> >  					DRM_PLANE_COMMIT_ACTIVE_ONLY);
> >  
> > +	drm_atomic_helper_fake_vblank(old_state);
> > +
> >  	drm_atomic_helper_commit_hw_done(old_state);
> >  
> >  	drm_atomic_helper_wait_for_vblanks(dev, old_state);
> > -- 
> > 2.14.1
> >   
>