6.6-stable review patch. If anyone has any objections, please let me know.
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From: Imre Deak imre.deak@intel.com
commit 12d8f318347b1d4feac48e8ac351d3786af39599 upstream.
The handling of the MST Connection Status Notify message is skipped if the probing of the topology is still pending. Acquiring the drm_dp_mst_topology_mgr::probe_lock for this in drm_dp_mst_handle_up_req() is problematic: the task/work this function is called from is also responsible for handling MST down-request replies (in drm_dp_mst_handle_down_rep()). Thus drm_dp_mst_link_probe_work() - holding already probe_lock - could be blocked waiting for an MST down-request reply while drm_dp_mst_handle_up_req() is waiting for probe_lock while processing a CSN message. This leads to the probe work's down-request message timing out.
A scenario similar to the above leading to a down-request timeout is handling a CSN message in drm_dp_mst_handle_conn_stat(), holding the probe_lock and sending down-request messages while a second CSN message sent by the sink subsequently is handled by drm_dp_mst_handle_up_req().
Fix the above by moving the logic to skip the CSN handling to drm_dp_mst_process_up_req(). This function is called from a work (separate from the task/work handling new up/down messages), already holding probe_lock. This solves the above timeout issue, since handling of down-request replies won't be blocked by probe_lock.
Fixes: ddf983488c3e ("drm/dp_mst: Skip CSN if topology probing is not done yet") Cc: Wayne Lin Wayne.Lin@amd.com Cc: Lyude Paul lyude@redhat.com Cc: stable@vger.kernel.org # v6.6+ Reviewed-by: Wayne Lin Wayne.Lin@amd.com Reviewed-by: Lyude Paul lyude@redhat.com Signed-off-by: Imre Deak imre.deak@intel.com Link: https://patchwork.freedesktop.org/patch/msgid/20250307183152.3822170-1-imre.... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/gpu/drm/display/drm_dp_mst_topology.c | 40 +++++++++++++++----------- 1 file changed, 24 insertions(+), 16 deletions(-)
--- a/drivers/gpu/drm/display/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c @@ -3959,6 +3959,22 @@ out: return 0; }
+static bool primary_mstb_probing_is_done(struct drm_dp_mst_topology_mgr *mgr) +{ + bool probing_done = false; + + mutex_lock(&mgr->lock); + + if (mgr->mst_primary && drm_dp_mst_topology_try_get_mstb(mgr->mst_primary)) { + probing_done = mgr->mst_primary->link_address_sent; + drm_dp_mst_topology_put_mstb(mgr->mst_primary); + } + + mutex_unlock(&mgr->lock); + + return probing_done; +} + static inline bool drm_dp_mst_process_up_req(struct drm_dp_mst_topology_mgr *mgr, struct drm_dp_pending_up_req *up_req) @@ -3989,8 +4005,12 @@ drm_dp_mst_process_up_req(struct drm_dp_
/* TODO: Add missing handler for DP_RESOURCE_STATUS_NOTIFY events */ if (msg->req_type == DP_CONNECTION_STATUS_NOTIFY) { - dowork = drm_dp_mst_handle_conn_stat(mstb, &msg->u.conn_stat); - hotplug = true; + if (!primary_mstb_probing_is_done(mgr)) { + drm_dbg_kms(mgr->dev, "Got CSN before finish topology probing. Skip it.\n"); + } else { + dowork = drm_dp_mst_handle_conn_stat(mstb, &msg->u.conn_stat); + hotplug = true; + } }
drm_dp_mst_topology_put_mstb(mstb); @@ -4069,10 +4089,11 @@ static int drm_dp_mst_handle_up_req(stru drm_dp_send_up_ack_reply(mgr, mst_primary, up_req->msg.req_type, false);
+ drm_dp_mst_topology_put_mstb(mst_primary); + if (up_req->msg.req_type == DP_CONNECTION_STATUS_NOTIFY) { const struct drm_dp_connection_status_notify *conn_stat = &up_req->msg.u.conn_stat; - bool handle_csn;
drm_dbg_kms(mgr->dev, "Got CSN: pn: %d ldps:%d ddps: %d mcs: %d ip: %d pdt: %d\n", conn_stat->port_number, @@ -4081,16 +4102,6 @@ static int drm_dp_mst_handle_up_req(stru conn_stat->message_capability_status, conn_stat->input_port, conn_stat->peer_device_type); - - mutex_lock(&mgr->probe_lock); - handle_csn = mst_primary->link_address_sent; - mutex_unlock(&mgr->probe_lock); - - if (!handle_csn) { - drm_dbg_kms(mgr->dev, "Got CSN before finish topology probing. Skip it."); - kfree(up_req); - goto out_put_primary; - } } else if (up_req->msg.req_type == DP_RESOURCE_STATUS_NOTIFY) { const struct drm_dp_resource_status_notify *res_stat = &up_req->msg.u.resource_stat; @@ -4105,9 +4116,6 @@ static int drm_dp_mst_handle_up_req(stru list_add_tail(&up_req->next, &mgr->up_req_list); mutex_unlock(&mgr->up_req_lock); queue_work(system_long_wq, &mgr->up_req_work); - -out_put_primary: - drm_dp_mst_topology_put_mstb(mst_primary); out_clear_reply: memset(&mgr->up_req_recv, 0, sizeof(struct drm_dp_sideband_msg_rx)); return 0;