Re: [PATCH v5 07/14] drm/dp_mst: Don't forget to update port->input in drm_dp_mst_handle_conn_stat()

Sean Paul
2019-10-22T20:14:35Z

On Mon, Oct 21, 2019 at 10:36:02PM -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 Syrjälä <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>
> Reviewed-by: Sean Paul <sean@poorly.run>
> ---
> drivers/gpu/drm/drm_dp_mst_topology.c | 52 +++++++++++++++++++--------
> 1 file changed, 38 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 7bf4db91ff90..c8e218b902ae 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -2079,18 +2079,40 @@ drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb,
> {
> struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
> struct drm_dp_mst_port *port;
> - int old_ddps;
> - bool dowork = false;
> + 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;
>
> - /* Locking is only needed if the port's exposed to userspace */
> - if (port->connector)
> + if (port->connector) {
> + if (!port->input && conn_stat->input_port) {
> + /*
> + * We can't remove a connector from an already exposed
> + * port, so just throw the port out and make sure we
> + * reprobe the link address of it's parent MSTB
> + */
> + drm_dp_mst_topology_unlink_port(mgr, port);
> + mstb->link_address_sent = false;
> + dowork = true;
> + goto out;
> + }
> +
> + /*
> + * Locking is only needed if the port's exposed to userspace
> + */

optional nit: this will still fit on one line

> drm_modeset_lock(&mgr->base.lock, NULL);
> + } else if (port->input && !conn_stat->input_port) {
> + create_connector = true;
> + /* Reprobe link address so we get num_sdp_streams */
> + mstb->link_address_sent = false;
> + dowork = true;
> + }
>
> 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;
> @@ -2103,21 +2125,23 @@ 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;
> }
>
> if (port->connector)
> drm_modeset_unlock(&mgr->base.lock);
> + else if (create_connector)
> + drm_dp_mst_port_add_connector(mstb, port);
>
> +out:
> drm_dp_mst_topology_put_port(port);
> if (dowork)
> queue_work(system_long_wq, &mstb->mgr->work);
> --
> 2.21.0
>

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