Re: [PATCH] drm/msm: Grab a vblank reference when waiting for commit_done

[Abhinav Kumar <abhinavk-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>]

On 2018-10-03 13:22, Sean Paul wrote:
> From: Sean Paul <seanpaul@chromium.org>
> 
> Similar to the atomic helpers, we should enable vblank while we're
> waiting for the commit to finish. DPU needs this, MDP5 seems to work
> fine without it.
> 
> Signed-off-by: Sean Paul <seanpaul@chromium.org>
> ---
As such I dont see any issue with this patch but I have a question 
overall on chrome vblank handling.
For a video mode panel, we will keep the HW resources enabled (including 
vsync related clocks) till device
is suspended.

The vblank_get and vblank_put are only controlling the 
register/deregister of the vblank IRQ callback which
send the events to the userspace and anything pending on vsync 
completion.

Does the chrome userspace turn ON/OFF the vblank using vblank_ctrl IOCTL 
Or does it guarantee it to be?

If so, is this patch just more of a safety check to make sure that vsync 
events remain ON till the frame is done?

Because HW wise it should be and this shouldnt be needed.

>  drivers/gpu/drm/msm/msm_atomic.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/msm_atomic.c 
> b/drivers/gpu/drm/msm/msm_atomic.c
> index c1f1779c980f..2b7bb6e166d3 100644
> --- a/drivers/gpu/drm/msm/msm_atomic.c
> +++ b/drivers/gpu/drm/msm/msm_atomic.c
> @@ -32,7 +32,12 @@ static void msm_atomic_wait_for_commit_done(struct
> drm_device *dev,
>  		if (!new_crtc_state->active)
>  			continue;
> 
> +		if (drm_crtc_vblank_get(crtc))
> +			continue;
> +
>  		kms->funcs->wait_for_crtc_commit_done(kms, crtc);
> +
> +		drm_crtc_vblank_put(crtc);
>  	}
>  }
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