[PATCH] V2: Currently, DRM get the capability of the mst hub only from DP_DPCD_REV and get the slower speed even the mst hub can run in the faster speed.

[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...@canonical.com>
---
ChangeLog:
1. use drm_dp_read_dpcd_caps instead.
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c 
b/drivers/gpu/drm/drm_dp_mst_topology.c
index 7753c718ddf9..293f71d0ae90 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -3694,8 +3694,8 @@ int drm_dp_mst_topology_mgr_set_mst(struct 
drm_dp_mst_topology_mgr *mgr, bool ms
                        ((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) {
+               ret = drm_dp_read_dpcd_caps(mgr->aux, mgr->dpcd);
+               if (ret < 0) {
                        DRM_DEBUG_KMS("failed to read DPCD\n");
                        goto out_unlock;
                }
-- 
2.25.1