[PATCH 2/2] drm/dp_mst: Avoid to mess up payload table by ports in stale topology

[Lyude Paul]

On Fri, 2021-05-28 at 21:55 +0800, Wayne Lin wrote:
> [Why]
> After unplug/hotplug hub from the system, userspace might start to
> clear stale payloads gradually. If we call drm_dp_mst_deallocate_vcpi()
> to release stale VCPI of those ports which are not relating to current
> topology, we have chane to wrongly clear active payload table entry for
> current topology.
> 
> E.g.
> We have allocated VCPI 1 in current payload table and we call
> drm_dp_mst_deallocate_vcpi() to clean VCPI 1 in stale topology. In
> drm_dp_mst_deallocate_vcpi(), it will call drm_dp_mst_put_payload_id()
> tp put VCPI 1 and which means ID 1 is available again. Thereafter, if we
> want to allocate a new payload stream, it will find ID 1 is available by
> drm_dp_mst_assign_payload_id(). However, ID 1 is being used
> 
> [How]
> Check target sink is relating to current topology or not before doing
> any payload table update.
> Searching upward to find the target sink's relevant root branch device.
> If the found root branch device is not the same root of current
> topology, don't update payload table.
> 
> Signed-off-by: Wayne Lin <Wayne.Lin at amd.com>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 29 +++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 5fc261014a20..3d988d54df89 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -94,6 +94,9 @@ static int drm_dp_mst_register_i2c_bus(struct
> drm_dp_mst_port *port);
>  static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_mst_port *port);
>  static void drm_dp_mst_kick_tx(struct drm_dp_mst_topology_mgr *mgr);
>  
> +static bool drm_dp_mst_port_downstream_of_branch(struct drm_dp_mst_port
> *port,
> +                                                struct drm_dp_mst_branch
> *branch);
> +
>  #define DBG_PREFIX "[dp_mst]"
>  
>  #define DP_STR(x) [DP_ ## x] = #x
> @@ -3360,6 +3363,7 @@ int drm_dp_update_payload_part1(struct
> drm_dp_mst_topology_mgr *mgr)
>         struct drm_dp_mst_port *port;
>         int i, j;
>         int cur_slots = 1;
> +       bool skip;
>  
>         mutex_lock(&mgr->payload_lock);
>         for (i = 0; i < mgr->max_payloads; i++) {
> @@ -3374,6 +3378,14 @@ int drm_dp_update_payload_part1(struct
> drm_dp_mst_topology_mgr *mgr)
>                         port = container_of(vcpi, struct drm_dp_mst_port,
>                                             vcpi);
>  
> +                       mutex_lock(&mgr->lock);
> +                       skip = !drm_dp_mst_port_downstream_of_branch(port,
> mgr->mst_primary);
> +                       mutex_unlock(&mgr->lock);
> +
> +                       if (skip) {
> +                               DRM_DEBUG_KMS("Virtual channel %d is not in
> current topology\n", i);

sorry I totally missed this on my first look - but this is the wrong debugging
macro (drm_dbg_kms() should be used) and as well, this patch doesn't actually
apply because it needs to be rebased against drm-tip. Could you fix this,
rebase the patches, and send a new version along with the fixes tags I
mentioned earlier? You can generate them using the dim tool here:

https://drm.pages.freedesktop.org/maintainer-tools/committer-drm-intel.html#labeling-fixes-before-pushing

> +                               continue;
> +                       }
>                         /* Validated ports don't matter if we're releasing
>                          * VCPI
>                          */
> @@ -3473,6 +3485,7 @@ int drm_dp_update_payload_part2(struct
> drm_dp_mst_topology_mgr *mgr)
>         struct drm_dp_mst_port *port;
>         int i;
>         int ret = 0;
> +       bool skip;
>  
>         mutex_lock(&mgr->payload_lock);
>         for (i = 0; i < mgr->max_payloads; i++) {
> @@ -3482,6 +3495,13 @@ int drm_dp_update_payload_part2(struct
> drm_dp_mst_topology_mgr *mgr)
>  
>                 port = container_of(mgr->proposed_vcpis[i], struct
> drm_dp_mst_port, vcpi);
>  
> +               mutex_lock(&mgr->lock);
> +               skip = !drm_dp_mst_port_downstream_of_branch(port, mgr-
> >mst_primary);
> +               mutex_unlock(&mgr->lock);
> +
> +               if (skip)
> +                       continue;
> +
>                 DRM_DEBUG_KMS("payload %d %d\n", i, mgr-
> >payloads[i].payload_state);
>                 if (mgr->payloads[i].payload_state == DP_PAYLOAD_LOCAL) {
>                         ret = drm_dp_create_payload_step2(mgr, port, mgr-
> >proposed_vcpis[i]->vcpi, &mgr->payloads[i]);
> @@ -4562,9 +4582,18 @@ EXPORT_SYMBOL(drm_dp_mst_reset_vcpi_slots);
>  void drm_dp_mst_deallocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
>                                 struct drm_dp_mst_port *port)
>  {
> +       bool skip;
> +
>         if (!port->vcpi.vcpi)
>                 return;
>  
> +       mutex_lock(&mgr->lock);
> +       skip = !drm_dp_mst_port_downstream_of_branch(port, mgr->mst_primary);
> +       mutex_unlock(&mgr->lock);
> +
> +       if (skip)
> +               return;
> +
>         drm_dp_mst_put_payload_id(mgr, port->vcpi.vcpi);
>         port->vcpi.num_slots = 0;
>         port->vcpi.pbn = 0;

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat