[PATCH 1/2] 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>
[added aux name to drm_dbg_kms() call]
Signed-off-by: Lyude Paul <lyude at redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200922065313.4794-1-koba.ko@canonical.com
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 0401b2f47500..6982ecbf30b5 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -3686,9 +3686,10 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms
 		WARN_ON(mgr->mst_primary);
 
 		/* get dpcd info */
-		ret = drm_dp_dpcd_read(mgr->aux, DP_DPCD_REV, 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, "%s: failed to read DPCD, ret %d\n",
+				    mgr->aux->name, ret);
 			goto out_unlock;
 		}
 
-- 
2.25.1