linux-kernel - [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.

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Date:   Thu, 10 Sep 2020 14:36:40 +0800
From:   Koba Ko <koba.ko@...onical.com>
To:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Lyude Paul <lyude@...hat.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc:     anthony.wong@...onical.com
Subject: [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.

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@...onical.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