[PATCH 1/2] drm/display/dp: Add condition to enable/disable SSB in MST

[Arun R Murthy]

Signed-off-by: Arun R Murthy <arun.r.murthy at intel.com>
---
 drivers/gpu/drm/display/drm_dp_mst_topology.c | 30 ++++++++++++++-----
 1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
index 8ca01a6bf645..947abade05c7 100644
--- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
@@ -2315,7 +2315,6 @@ drm_dp_mst_add_port(struct drm_device *dev,
 	port->mgr = mgr;
 	port->aux.name = "DPMST";
 	port->aux.dev = dev->dev;
-	port->aux.is_remote = true;
 
 	/* initialize the MST downstream port's AUX crc work queue */
 	port->aux.drm_dev = dev;
@@ -3634,6 +3633,7 @@ EXPORT_SYMBOL(drm_dp_read_mst_cap);
  */
 int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool mst_state)
 {
+	u8 mstm_cap;
 	int ret = 0;
 	struct drm_dp_mst_branch *mstb = NULL;
 
@@ -3641,18 +3641,32 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms
 	if (mst_state == mgr->mst_state)
 		goto out_unlock;
 
+	/* get dpcd info */
+	ret = drm_dp_read_dpcd_caps(mgr->aux, mgr->dpcd);
+	if (ret < 0) {
+		drm_dbg_kms(mgr->dev, "%s: failed to read DPCD, ret %d\n",
+			    mgr->aux->name, ret);
+		goto out_unlock;
+	}
+
+	/**
+	 * MSTM_CAP dpcd reg 0x00021
+	 * Bit[0] : Bit[1]
+	 * 0:0   - 128/132b capable, support SST and not SSB
+	 * 0:1   - 128/132b capable, support SST and SSB
+	 * 1:x   - 128/132b capable, support MST and SSB
+	 */
+	drm_dp_dpcd_readb(mgr->aux, DP_MSTM_CAP, &mstm_cap);
+	if (mstm_cap & DP_SINGLE_STREAM_SIDEBAND_MSG)
+		mgr->aux->is_remote = true;
+	else
+		mgr->aux->is_remote = true;
+
 	mgr->mst_state = mst_state;
 	/* set the device into MST mode */
 	if (mst_state) {
 		WARN_ON(mgr->mst_primary);
 
-		/* get dpcd info */
-		ret = drm_dp_read_dpcd_caps(mgr->aux, mgr->dpcd);
-		if (ret < 0) {
-			drm_dbg_kms(mgr->dev, "%s: failed to read DPCD, ret %d\n",
-				    mgr->aux->name, ret);
-			goto out_unlock;
-		}
 
 		/* add initial branch device at LCT 1 */
 		mstb = drm_dp_add_mst_branch_device(1, NULL);
-- 
2.25.1