linux-kernel - Re: [PATCH 2/2] drm/atomic: clear new_state pointers at hw_done

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Date:   Fri, 1 Nov 2019 21:24:58 +0200
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Rob Clark <robdclark@...il.com>
Cc:     dri-devel@...ts.freedesktop.org,
        Rob Clark <robdclark@...omium.org>,
        David Airlie <airlied@...ux.ie>,
        open list <linux-kernel@...r.kernel.org>,
        Sean Paul <seanpaul@...omium.org>, Sean Paul <sean@...rly.run>
Subject: Re: [PATCH 2/2] drm/atomic: clear new_state pointers at hw_done

On Fri, Nov 01, 2019 at 11:07:13AM -0700, Rob Clark wrote:
> From: Rob Clark <robdclark@...omium.org>
> 
> The new state should not be accessed after this point.  Clear the
> pointers to make that explicit.
> 
> This makes the error corrected in the previous patch more obvious.
> 
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 732bd0ce9241..176831df8163 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -2234,13 +2234,42 @@ EXPORT_SYMBOL(drm_atomic_helper_fake_vblank);
>   */
>  void drm_atomic_helper_commit_hw_done(struct drm_atomic_state *old_state)
>  {
> +	struct drm_connector *connector;
> +	struct drm_connector_state *old_conn_state, *new_conn_state;
>  	struct drm_crtc *crtc;
>  	struct drm_crtc_state *old_crtc_state, *new_crtc_state;
> +	struct drm_plane *plane;
> +	struct drm_plane_state *old_plane_state, *new_plane_state;
>  	struct drm_crtc_commit *commit;
> +	struct drm_private_obj *obj;
> +	struct drm_private_state *old_obj_state, *new_obj_state;
>  	int i;
>  
> +	/*
> +	 * After this point, drivers should not access the permanent modeset
> +	 * state, so we also clear the new_state pointers to make this
> +	 * restriction explicit.
> +	 *
> +	 * For the CRTC state, we do this in the same loop where we signal
> +	 * hw_done, since we still need to new_crtc_state to fish out the
> +	 * commit.
> +	 */
> +
> +	for_each_oldnew_connector_in_state(old_state, connector, old_conn_state, new_conn_state, i) {
> +		old_state->connectors[i].new_state = NULL;
> +	}
> +
> +	for_each_oldnew_plane_in_state(old_state, plane, old_plane_state, new_plane_state, i) {
> +		old_state->planes[i].new_state = NULL;
> +	}
> +
> +	for_each_oldnew_private_obj_in_state(old_state, obj, old_obj_state, new_obj_state, i) {
> +		old_state->private_objs[i].new_state = NULL;
> +	}
> +
>  	for_each_oldnew_crtc_in_state(old_state, crtc, old_crtc_state, new_crtc_state, i) {
>  		old_state->crtcs[i].new_self_refresh_active = new_crtc_state->self_refresh_active;
> +		old_state->crtcs[i].new_state = NULL;

That's going to be a real PITA when doing programming after the fact from
a vblank worker. It's already a pain that the new_crtc_state->state is
getting NULLed somewhere.

>  
>  		commit = new_crtc_state->commit;
>  		if (!commit)
> -- 
> 2.21.0
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Ville Syrjälä
Intel

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