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

[Daniel Vetter <daniel@ffwll.ch>]

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@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.
-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
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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