On Wed, Mar 04, 2020 at 05:36:12PM -0500, Lyude Paul wrote:
It's next to impossible for us to do connector probing on topologies without occasionally racing with userspace, since creating a connector itself causes a hotplug event which we have to send before probing the available PBN of a connector. Even if we didn't have this hotplug event sent, there's still always a chance that userspace started probing connectors before we finished probing the topology.
This can be a problem when validating a new MST state since the connector will be shown as connected briefly, but without any available PBN - causing any atomic state which would enable said connector to fail with -ENOSPC. So, let's simply workaround this by telling userspace new MST connectors are disconnected until we've finished probing their PBN. Since we always send a hotplug event at the end of the link address probing process, userspace will still know to reprobe the connector when we're ready.
Signed-off-by: Lyude Paul lyude@redhat.com Fixes: cd82d82cbc04 ("drm/dp_mst: Add branch bandwidth validation to MST atomic check") Cc: Mikita Lipski mikita.lipski@amd.com Cc: Alex Deucher alexander.deucher@amd.com Cc: Sean Paul seanpaul@google.com Cc: Hans de Goede hdegoede@redhat.com
drivers/gpu/drm/drm_dp_mst_topology.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index 207eef08d12c..7b0ff0cff954 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -4033,6 +4033,19 @@ drm_dp_mst_detect_port(struct drm_connector *connector, ret = connector_status_connected; break; }
- /* We don't want to tell userspace the port is actually plugged into
* anything until we've finished probing it's available_pbn, otherwise
"its"
Why is the connector even registered before we've finished the probe?
* userspace will see racy atomic check failures** Since we always send a hotplug at the end of probing topology* state, we can just let userspace reprobe this connector later.*/- if (ret == connector_status_connected && !port->available_pbn) {
DRM_DEBUG_KMS("[CONNECTOR:%d:%s] not ready yet (PBN not probed)\n",connector->base.id, connector->name);ret = connector_status_disconnected;- }
out: drm_dp_mst_topology_put_port(port); return ret; -- 2.24.1
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