linux-kernel - Re: [PATCH] drm/vkms: add wait_for_vblanks in atomic_commit

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Date:   Thu, 2 Jul 2020 15:13:55 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Sidong Yang <realwakka@...il.com>
Cc:     Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>,
        Emil Velikov <emil.l.velikov@...il.com>,
        Haneen Mohammed <hamohammed.sa@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/vkms: add wait_for_vblanks in atomic_commit_tail

On Wed, Jul 01, 2020 at 03:31:34PM +0000, Sidong Yang wrote:
> there is an error when igt test is run continuously. vkms_atomic_commit_tail()
> need to call drm_atomic_helper_wait_for_vblanks() for give up ownership of
> vblank events. without this code, next atomic commit will not enable vblank
> and raise timeout error.
> 
> Signed-off-by: Sidong Yang <realwakka@...il.com>
> ---
>  drivers/gpu/drm/vkms/vkms_drv.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
> index 1e8b2169d834..10b9be67a068 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.c
> +++ b/drivers/gpu/drm/vkms/vkms_drv.c
> @@ -93,6 +93,8 @@ static void vkms_atomic_commit_tail(struct drm_atomic_state *old_state)
>  		flush_work(&vkms_state->composer_work);
>  	}
>  
> +	drm_atomic_helper_wait_for_vblanks(dev, old_state);

Uh, we have a wait_for_flip_done right above, which should be doing
exactly the same, but more precisely: Instead of just waiting for any
vblank to happen, we wait for exactly the vblank corresponding to this
atomic commit. So no races possible. If this is papering over some issue,
then I think more debugging is needed.

What exactly is going wrong here for you?
-Daniel

> +
>  	drm_atomic_helper_cleanup_planes(dev, old_state);
>  }
>  
> -- 
> 2.17.1
> 

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