linux-kernel - Re: [RFC 3/4] drm/atomic-helper: Set fence deadline for vblank

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Date:   Tue, 27 Jul 2021 12:44:55 +0200
From:   Michel Dänzer <michel@...nzer.net>
To:     Rob Clark <robdclark@...il.com>
Cc:     Matthew Brost <matthew.brost@...el.com>,
        Rob Clark <robdclark@...omium.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Christian König <ckoenig.leichtzumerken@...il.com>,
        open list <linux-kernel@...r.kernel.org>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [RFC 3/4] drm/atomic-helper: Set fence deadline for vblank

On 2021-07-27 1:38 a.m., Rob Clark wrote:
> From: Rob Clark <robdclark@...omium.org>
> 
> For an atomic commit updating a single CRTC (ie. a pageflip) calculate
> the next vblank time, and inform the fence(s) of that deadline.
> 
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 36 +++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index bc3487964fb5..f81b20775b15 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1406,6 +1406,40 @@ void drm_atomic_helper_commit_modeset_enables(struct drm_device *dev,
>  }
>  EXPORT_SYMBOL(drm_atomic_helper_commit_modeset_enables);
>  
> +/*
> + * For atomic updates which touch just a single CRTC, calculate the time of the
> + * next vblank, and inform all the fences of the of the deadline.
> + */
> +static void set_fence_deadline(struct drm_device *dev,
> +			       struct drm_atomic_state *state)
> +{
> +	struct drm_crtc *crtc, *wait_crtc = NULL;
> +	struct drm_crtc_state *new_crtc_state;
> +	struct drm_plane *plane;
> +	struct drm_plane_state *new_plane_state;
> +	ktime_t vbltime;
> +	int i;
> +
> +	for_each_new_crtc_in_state (state, crtc, new_crtc_state, i) {
> +		if (!wait_crtc)
> +			return;

Either this return or the next one below would always be taken, I doubt this was intended.


> +		wait_crtc = crtc;
> +	}
> +
> +	/* If no CRTCs updated, then nothing to do: */
> +	if (!wait_crtc)
> +		return;
> +
> +	if (drm_crtc_next_vblank_time(wait_crtc, &vbltime))
> +		return;
> +
> +	for_each_new_plane_in_state (state, plane, new_plane_state, i) {
> +		if (!new_plane_state->fence)
> +			continue;
> +		dma_fence_set_deadline(new_plane_state->fence, vbltime);
> +	}

vblank timestamps correspond to the end of vertical blank, the deadline should be the start of vertical blank though.


-- 
Earthling Michel Dänzer               |               https://redhat.com
Libre software enthusiast             |             Mesa and X developer