[PATCH v3] drm/dp_mst: Retrieve extended DPCD caps for topology manager

[Koba Ko]

As per DP-1.3, First check DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT.
If DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT is 1, read the DP_DP13_DPCD_REV to
get the faster capability.
If DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT is 0, read DP_DPCD_REV.

Signed-off-by: Koba Ko <koba.ko at canonical.com>
Reviewed-by: Lyude Paul <lyude at redhat.com>
---
Changelog:
1. Adjust the commit message.
2. use drm_dbg_kms instead and print the return code.
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 7753c718ddf9..63f8809b9aa4 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -3671,8 +3671,6 @@ 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)
 {
 	int ret = 0;
-	u8 dpcd_ext = 0;
-	unsigned int dpcd_offset = 0;
 	struct drm_dp_mst_branch *mstb = NULL;
 
 	mutex_lock(&mgr->payload_lock);
@@ -3686,17 +3684,11 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms
 		struct drm_dp_payload reset_pay;
 
 		WARN_ON(mgr->mst_primary);
-		drm_dp_dpcd_read(mgr->aux,
-				 DP_TRAINING_AUX_RD_INTERVAL,
-				 &dpcd_ext, sizeof(dpcd_ext));
-
-		dpcd_offset =
-			((dpcd_ext & DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT) ?  DP_DP13_DPCD_REV : DP_DPCD_REV);
 
 		/* get dpcd info */
-		ret = drm_dp_dpcd_read(mgr->aux, dpcd_offset, mgr->dpcd, DP_RECEIVER_CAP_SIZE);
-		if (ret != DP_RECEIVER_CAP_SIZE) {
-			DRM_DEBUG_KMS("failed to read DPCD\n");
+		ret = drm_dp_read_dpcd_caps(mgr->aux, mgr->dpcd);
+		if (ret < 0) {
+			drm_dbg_kms(mgr->dev, "failed to read DPCD, ret %d\n", ret);
 			goto out_unlock;
 		}
 
-- 
2.25.1