drm/amd/display: Detect dpcd_rev when hotplug mst monitor

[Why]
Once mst topology is constructed, later on new connected monitors
are reported to source by CSN message. Within CSN, there is no
carried info of DPCD_REV comparing to LINK_ADDRESS reply. As the
result, we might leave some ports connected to DP but without DPCD
revision number which will affect us determining the capability of
the DP Rx.

[How]
Send out remote DPCD read when the port's dpcd_rev is 0x0 in
detect_ctx(). Firstly, read out the value from DPCD 0x2200. If the
return value is 0x0, it's likely the DP1.2 DP Rx then we reques
revision from DPCD 0x0 again.

Reviewed-by: Hersen Wu <hersenwu@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
index 9221b6690a4a920e3bf60a204e6a162a8f64cc56..a6d551ff89d1f0e8f06f62a303744f7c8bcb7de3 100644 (file)
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
@@ -344,12 +344,48 @@ dm_dp_mst_detect(struct drm_connector *connector,
 {
        struct amdgpu_dm_connector *aconnector = to_amdgpu_dm_connector(connector);
        struct amdgpu_dm_connector *master = aconnector->mst_port;
+       struct drm_dp_mst_port *port = aconnector->port;
+       int connection_status;
 
        if (drm_connector_is_unregistered(connector))
                return connector_status_disconnected;
 
-       return drm_dp_mst_detect_port(connector, ctx, &master->mst_mgr,
+       connection_status = drm_dp_mst_detect_port(connector, ctx, &master->mst_mgr,
                                      aconnector->port);
+
+       if (port->pdt != DP_PEER_DEVICE_NONE && !port->dpcd_rev) {
+               uint8_t dpcd_rev;
+               int ret;
+
+               ret = drm_dp_dpcd_readb(&port->aux, DP_DP13_DPCD_REV, &dpcd_rev);
+
+               if (ret == 1) {
+                       port->dpcd_rev = dpcd_rev;
+
+                       /* Could be DP1.2 DP Rx case*/
+                       if (!dpcd_rev) {
+                               ret = drm_dp_dpcd_readb(&port->aux, DP_DPCD_REV, &dpcd_rev);
+
+                               if (ret == 1)
+                                       port->dpcd_rev = dpcd_rev;
+                       }
+
+                       if (!dpcd_rev)
+                               DRM_DEBUG_KMS("Can't decide DPCD revision number!");
+               }
+
+               /*
+                * Could be legacy sink, logical port etc on DP1.2.
+                * Will get Nack under these cases when issue remote
+                * DPCD read.
+                */
+               if (ret != 1)
+                       DRM_DEBUG_KMS("Can't access DPCD");
+       } else if (port->pdt == DP_PEER_DEVICE_NONE) {
+               port->dpcd_rev = 0;
+       }
+
+       return connection_status;
 }
 
 static int dm_dp_mst_atomic_check(struct drm_connector *connector,