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Subject: Re: [PATCH v4 1/5] drm/rockchip: fix fb references in async update
To:     dri-devel@lists.freedesktop.org, nicholas.kazlauskas@amd.com
Cc:     andrey.grodzovsky@amd.com, daniel.vetter@ffwll.ch,
        linux-kernel@vger.kernel.org, Tomasz Figa <tfiga@chromium.org>,
        boris.brezillon@collabora.com, David Airlie <airlied@linux.ie>,
        Sean Paul <seanpaul@google.com>, kernel@collabora.com,
        harry.wentland@amd.com,
        =?UTF-8?Q?St=c3=a9phane_Marchesin?= <marcheu@google.com>,
        Sandy Huang <hjc@rock-chips.com>,
        linux-rockchip@lists.infradead.org,
        =?UTF-8?Q?Heiko_St=c3=bcbner?= <heiko@sntech.de>,
        linux-arm-kernel@lists.infradead.org,
        Daniel Vetter <daniel@ffwll.ch>
References: <20190603165610.24614-1-helen.koike@collabora.com>
 <20190603165610.24614-2-helen.koike@collabora.com>
From:   Helen Koike <helen.koike@collabora.com>
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Message-ID: <aecadca2-f67b-5d9d-550e-f90cbca5fd3f@collabora.com>
Date:   Mon, 3 Jun 2019 17:13:34 -0300
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On 6/3/19 1:56 PM, Helen Koike wrote:
> In the case of async update, modifications are done in place, i.e. in the
> current plane state, so the new_state is prepared and the new_state is
> cleaned up (instead of the old_state, unlike what happens in a
> normal sync update).
> To cleanup the old_fb properly, it needs to be placed in the new_state
> in the end of async_update, so cleanup call will unreference the old_fb
> correctly.
> 
> Also, the previous code had a:
> 
> 	plane_state = plane->funcs->atomic_duplicate_state(plane);
> 	...
> 	swap(plane_state, plane->state);
> 
> 	if (plane->state->fb && plane->state->fb != new_state->fb) {
> 	...
> 	}
> 
> Which was wrong, as the fb were just assigned to be equal, so this if
> statement nevers evaluates to true.
> 
> Another details is that the function drm_crtc_vblank_get() can only be
> called when vop->is_enabled is true, otherwise it has no effect and
> trows a WARN_ON().
> 
> Calling drm_atomic_set_fb_for_plane() (which get a referent of the new
> fb and pus the old fb) is not required, as it is taken care by
> drm_mode_cursor_universal() when calling
> drm_atomic_helper_update_plane().
> 
> Signed-off-by: Helen Koike <helen.koike@collabora.com>

Cc: <stable@vger.kernel.org> # v4.20+
Fixes: 15609559a834 ("drm/rockchip: update cursors asynchronously
through atomic.")

> 
> ---
> Hello,
> 
> I tested on the rockchip ficus v1.1 using igt plane_cursor_legacy and
> kms_cursor_legacy and I didn't see any regressions.
> 
> Changes in v4: None
> Changes in v3:
> - use swap() to swap old and new framebuffers in async_update
> - get the reference to old_fb and set the worker after vop_plane_atomic_update()
> - add a FIXME tag for when we have multiple fbs to be released when
> vblank happens.
> - update commit message
> 
> Changes in v2: None
> 
>  drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 51 +++++++++++----------
>  1 file changed, 26 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> index 4189ca17f381..b7c47d1153c6 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> @@ -919,29 +919,17 @@ static void vop_plane_atomic_async_update(struct drm_plane *plane,
>  					  struct drm_plane_state *new_state)
>  {
>  	struct vop *vop = to_vop(plane->state->crtc);
> -	struct drm_plane_state *plane_state;
> -
> -	plane_state = plane->funcs->atomic_duplicate_state(plane);
> -	plane_state->crtc_x = new_state->crtc_x;
> -	plane_state->crtc_y = new_state->crtc_y;
> -	plane_state->crtc_h = new_state->crtc_h;
> -	plane_state->crtc_w = new_state->crtc_w;
> -	plane_state->src_x = new_state->src_x;
> -	plane_state->src_y = new_state->src_y;
> -	plane_state->src_h = new_state->src_h;
> -	plane_state->src_w = new_state->src_w;
> -
> -	if (plane_state->fb != new_state->fb)
> -		drm_atomic_set_fb_for_plane(plane_state, new_state->fb);
> -
> -	swap(plane_state, plane->state);
> -
> -	if (plane->state->fb && plane->state->fb != new_state->fb) {
> -		drm_framebuffer_get(plane->state->fb);
> -		WARN_ON(drm_crtc_vblank_get(plane->state->crtc) != 0);
> -		drm_flip_work_queue(&vop->fb_unref_work, plane->state->fb);
> -		set_bit(VOP_PENDING_FB_UNREF, &vop->pending);
> -	}
> +	struct drm_framebuffer *old_fb = plane->state->fb;
> +
> +	plane->state->crtc_x = new_state->crtc_x;
> +	plane->state->crtc_y = new_state->crtc_y;
> +	plane->state->crtc_h = new_state->crtc_h;
> +	plane->state->crtc_w = new_state->crtc_w;
> +	plane->state->src_x = new_state->src_x;
> +	plane->state->src_y = new_state->src_y;
> +	plane->state->src_h = new_state->src_h;
> +	plane->state->src_w = new_state->src_w;
> +	swap(plane->state->fb, new_state->fb);
>  
>  	if (vop->is_enabled) {
>  		rockchip_drm_psr_inhibit_get_state(new_state->state);
> @@ -950,9 +938,22 @@ static void vop_plane_atomic_async_update(struct drm_plane *plane,
>  		vop_cfg_done(vop);
>  		spin_unlock(&vop->reg_lock);
>  		rockchip_drm_psr_inhibit_put_state(new_state->state);
> -	}
>  
> -	plane->funcs->atomic_destroy_state(plane, plane_state);
> +		/*
> +		 * A scanout can still be occurring, so we can't drop the
> +		 * reference to the old framebuffer. To solve this we get a
> +		 * reference to old_fb and set a worker to release it later.
> +		 * FIXME: if we perform 500 async_update calls before the
> +		 * vblank, then we can have 500 different framebuffers waiting
> +		 * to be released.
> +		 */
> +		if (old_fb && plane->state->fb != old_fb) {
> +			drm_framebuffer_get(old_fb);
> +			WARN_ON(drm_crtc_vblank_get(plane->state->crtc) != 0);
> +			drm_flip_work_queue(&vop->fb_unref_work, old_fb);
> +			set_bit(VOP_PENDING_FB_UNREF, &vop->pending);
> +		}
> +	}
>  }
>  
>  static const struct drm_plane_helper_funcs plane_helper_funcs = {
>