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Date:   Wed, 25 Sep 2019 16:03:27 -0400
From:   Sean Paul <sean@poorly.run>
To:     Lyude Paul <lyude@redhat.com>
Cc:     dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org,
        amd-gfx@lists.freedesktop.org, Juston Li <juston.li@intel.com>,
        Imre Deak <imre.deak@intel.com>,
        Ville =?iso-8859-1?Q?Syrj=E4l=E4?= 
        <ville.syrjala@linux.intel.com>, Harry Wentland <hwentlan@amd.com>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 21/27] drm/dp_mst: Don't forget to update port->input
 in drm_dp_mst_handle_conn_stat()
Message-ID: <20190925200327.GM218215@art_vandelay>
References: <20190903204645.25487-1-lyude@redhat.com>
 <20190903204645.25487-22-lyude@redhat.com>
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On Tue, Sep 03, 2019 at 04:45:59PM -0400, Lyude Paul wrote:
> This probably hasn't caused any problems up until now since it's
> probably nearly impossible to encounter this in the wild, however if we
> were to receive a connection status notification from the MST hub after
> resume while we're in the middle of reprobing the link addresses for a
> topology then there's a much larger chance that a port could have
> changed from being an output port to input port (or vice versa). If we
> forget to update this bit of information, we'll potentially ignore a
> valid PDT change on a downstream port because we think it's an input
> port.
> 
> So, make sure we read the input_port field in connection status
> notifications in drm_dp_mst_handle_conn_stat() to prevent this from
> happening once we've implemented suspend/resume reprobing.
> 
> Cc: Juston Li <juston.li@intel.com>
> Cc: Imre Deak <imre.deak@intel.com>
> Cc: Ville Syrj?l? <ville.syrjala@linux.intel.com>
> Cc: Harry Wentland <hwentlan@amd.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Signed-off-by: Lyude Paul <lyude@redhat.com>

Nice catch! Same comment here re: port->mutex, but we can sort that out on the
other thread

Reviewed-by: Sean Paul <sean@poorly.run>


> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 51 +++++++++++++++++++--------
>  1 file changed, 37 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 259634c5d6dc..e407aba1fbd2 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -2078,18 +2078,23 @@ static void
>  drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb,
>  			    struct drm_dp_connection_status_notify *conn_stat)
>  {
> -	struct drm_device *dev = mstb->mgr->dev;
> +	struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
> +	struct drm_device *dev = mgr->dev;
>  	struct drm_dp_mst_port *port;
> -	int old_ddps;
> -	bool dowork = false;
> +	struct drm_connector *connector_to_destroy = NULL;
> +	int old_ddps, ret;
> +	u8 new_pdt;
> +	bool dowork = false, create_connector = false;
>  
>  	port = drm_dp_get_port(mstb, conn_stat->port_number);
>  	if (!port)
>  		return;
>  
> +	mutex_lock(&port->lock);
>  	drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
>  
>  	old_ddps = port->ddps;
> +	port->input = conn_stat->input_port;
>  	port->mcs = conn_stat->message_capability_status;
>  	port->ldps = conn_stat->legacy_device_plug_status;
>  	port->ddps = conn_stat->displayport_device_plug_status;
> @@ -2102,23 +2107,41 @@ drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb,
>  		}
>  	}
>  
> -	if (!port->input) {
> -		int ret = drm_dp_port_set_pdt(port,
> -					      conn_stat->peer_device_type);
> -		if (ret == 1) {
> -			dowork = true;
> -		} else if (ret < 0) {
> -			DRM_ERROR("Failed to change PDT for port %p: %d\n",
> -				  port, ret);
> -			dowork = false;
> -		}
> +	new_pdt = port->input ? DP_PEER_DEVICE_NONE : conn_stat->peer_device_type;
> +
> +	ret = drm_dp_port_set_pdt(port, new_pdt);
> +	if (ret == 1) {
> +		dowork = true;
> +	} else if (ret < 0) {
> +		DRM_ERROR("Failed to change PDT for port %p: %d\n",
> +			  port, ret);
> +		dowork = false;
> +	}
> +
> +	/*
> +	 * We unset port->connector before dropping connection_mutex so that
> +	 * there's no chance any of the atomic MST helpers can accidentally
> +	 * associate a to-be-destroyed connector with a port.
> +	 */
> +	if (port->connector && port->input) {
> +		connector_to_destroy = port->connector;
> +		port->connector = NULL;
> +	} else if (!port->connector && !port->input) {
> +		create_connector = true;
>  	}
>  
>  	drm_modeset_unlock(&dev->mode_config.connection_mutex);
> +
> +	if (connector_to_destroy)
> +		mgr->cbs->destroy_connector(mgr, connector_to_destroy);
> +	else if (create_connector)
> +		drm_dp_mst_port_add_connector(mstb, port);
> +
> +	mutex_unlock(&port->lock);
> +
>  	drm_dp_mst_topology_put_port(port);
>  	if (dowork)
>  		queue_work(system_long_wq, &mstb->mgr->work);
> -
>  }
>  
>  static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_topology_mgr *mgr,
> -- 
> 2.21.0
> 

-- 
Sean Paul, Software Engineer, Google / Chromium OS