With DP2.1, multistream packetization and the underneth MST protocol
will be required for SST. So check for MSTM_CAP to see if MST is really
required and skip the MSTM_CTRL write so that we ensure that only the
underneth protocol and the multistream packetization will be enabled and
sink will not be confused by a corresponding dpcd write.
Signed-off-by: Arun R Murthy <arun.r.mur...@intel.com>
---
drivers/gpu/drm/display/drm_dp_mst_topology.c | 38 +++++++++++--------
1 file changed, 22 insertions(+), 16 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..c5b3e51ea0c9 100644
--- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
@@ -3666,12 +3666,14 @@ int drm_dp_mst_topology_mgr_set_mst(struct
drm_dp_mst_topology_mgr *mgr, bool ms
mgr->mst_primary = mstb;
drm_dp_mst_topology_get_mstb(mgr->mst_primary);
- ret = drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
- DP_MST_EN |
- DP_UP_REQ_EN |
- DP_UPSTREAM_IS_SRC);
- if (ret < 0)
- goto out_unlock;
+ if (drm_dp_read_mst_cap(mgr->aux, mgr->dpcd)) {
+ ret = drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
+ DP_MST_EN |
+ DP_UP_REQ_EN |
+ DP_UPSTREAM_IS_SRC);
+ if (ret < 0)
+ goto out_unlock;
+ }
/* Write reset payload */
drm_dp_dpcd_write_payload(mgr, 0, 0, 0x3f);
@@ -3684,7 +3686,8 @@ int drm_dp_mst_topology_mgr_set_mst(struct
drm_dp_mst_topology_mgr *mgr, bool ms
mstb = mgr->mst_primary;
mgr->mst_primary = NULL;
/* this can fail if the device is gone */
- drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL, 0);
+ if (drm_dp_read_mst_cap(mgr->aux, mgr->dpcd))
+ drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL, 0);
ret = 0;
mgr->payload_id_table_cleared = false;
@@ -3724,8 +3727,9 @@ drm_dp_mst_topology_mgr_invalidate_mstb(struct
drm_dp_mst_branch *mstb)
void drm_dp_mst_topology_mgr_suspend(struct drm_dp_mst_topology_mgr *mgr)
{
mutex_lock(&mgr->lock);
- drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
- DP_MST_EN | DP_UPSTREAM_IS_SRC);
+ if (drm_dp_read_mst_cap(mgr->aux, mgr->dpcd))
+ drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
+ DP_MST_EN | DP_UPSTREAM_IS_SRC);
mutex_unlock(&mgr->lock);
flush_work(&mgr->up_req_work);
flush_work(&mgr->work);
@@ -3773,13 +3777,15 @@ int drm_dp_mst_topology_mgr_resume(struct
drm_dp_mst_topology_mgr *mgr,
goto out_fail;
}
- ret = drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
- DP_MST_EN |
- DP_UP_REQ_EN |
- DP_UPSTREAM_IS_SRC);
- if (ret < 0) {
- drm_dbg_kms(mgr->dev, "mst write failed - undocked during
suspend?\n");
- goto out_fail;
+ if (drm_dp_read_mst_cap(mgr->aux, mgr->dpcd)) {
+ ret = drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
+ DP_MST_EN |
+ DP_UP_REQ_EN |
+ DP_UPSTREAM_IS_SRC);
+ if (ret < 0) {
+ drm_dbg_kms(mgr->dev, "mst write failed - undocked
during suspend?\n");
+ goto out_fail;
+ }
}
/* Some hubs forget their guids after they resume */
--
2.25.1
