[PATCH 1/2] drm/dp_mst: Add a function to determine the mst end device

[Wayne Lin]

[Why]
For later usage convenience, add the function
drm_dp_mst_is_dp_mst_end_device() to decide whether a peer device
connected to a DFP is mst end device. Which also indicates if the peer
device is capable of handling message or not.

Signed-off-by: Wayne Lin <Wayne.Lin at amd.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index eebf325d7f48..8f54b241db08 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1918,6 +1918,22 @@ static u8 drm_dp_calculate_rad(struct drm_dp_mst_port *port,
 	return parent_lct + 1;
 }
 
+static bool drm_dp_mst_is_dp_mst_end_device(u8 pdt, bool mcs)
+{
+	switch (pdt) {
+	case DP_PEER_DEVICE_DP_LEGACY_CONV:
+	case DP_PEER_DEVICE_SST_SINK:
+		return true;
+	case DP_PEER_DEVICE_MST_BRANCHING:
+		/* For sst branch device */
+		if (!mcs)
+			return true;
+
+		return false;
+	}
+	return true;
+}
+
 static int drm_dp_port_set_pdt(struct drm_dp_mst_port *port, u8 new_pdt)
 {
 	struct drm_dp_mst_topology_mgr *mgr = port->mgr;
-- 
2.17.1