1 files changed, 232 insertions, 76 deletions

diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
index c490e8befc2f..3577786b5db2 100644
--- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
@@ -43,6 +43,7 @@
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_drv.h>
 #include <drm/drm_edid.h>
+#include <drm/drm_fixed.h>
 #include <drm/drm_print.h>
 #include <drm/drm_probe_helper.h>
 
@@ -1305,7 +1306,8 @@ static int drm_dp_mst_wait_tx_reply(struct drm_dp_mst_branch *mstb,
 	}
 out:
 	if (unlikely(ret == -EIO) && drm_debug_enabled(DRM_UT_DP)) {
-		struct drm_printer p = drm_debug_printer(DBG_PREFIX);
+		struct drm_printer p = drm_dbg_printer(mgr->dev, DRM_UT_DP,
+						       DBG_PREFIX);
 
 		drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
 	}
@@ -1592,10 +1594,11 @@ topology_ref_type_to_str(enum drm_dp_mst_topology_ref_type type)
 }
 
 static void
-__dump_topology_ref_history(struct drm_dp_mst_topology_ref_history *history,
+__dump_topology_ref_history(struct drm_device *drm,
+			    struct drm_dp_mst_topology_ref_history *history,
 			    void *ptr, const char *type_str)
 {
-	struct drm_printer p = drm_debug_printer(DBG_PREFIX);
+	struct drm_printer p = drm_dbg_printer(drm, DRM_UT_DP, DBG_PREFIX);
 	char *buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
 	int i;
 
@@ -1637,15 +1640,15 @@ out:
 static __always_inline void
 drm_dp_mst_dump_mstb_topology_history(struct drm_dp_mst_branch *mstb)
 {
-	__dump_topology_ref_history(&mstb->topology_ref_history, mstb,
-				    "MSTB");
+	__dump_topology_ref_history(mstb->mgr->dev, &mstb->topology_ref_history,
+				    mstb, "MSTB");
 }
 
 static __always_inline void
 drm_dp_mst_dump_port_topology_history(struct drm_dp_mst_port *port)
 {
-	__dump_topology_ref_history(&port->topology_ref_history, port,
-				    "Port");
+	__dump_topology_ref_history(port->mgr->dev, &port->topology_ref_history,
+				    port, "Port");
 }
 
 static __always_inline void
@@ -2271,7 +2274,7 @@ drm_dp_mst_port_add_connector(struct drm_dp_mst_branch *mstb,
 
 	if (port->pdt != DP_PEER_DEVICE_NONE &&
 	    drm_dp_mst_is_end_device(port->pdt, port->mcs) &&
-	    port->port_num >= DP_MST_LOGICAL_PORT_0)
+	    drm_dp_mst_port_is_logical(port))
 		port->cached_edid = drm_edid_read_ddc(port->connector,
 						      &port->aux.ddc);
 
@@ -2574,14 +2577,14 @@ static struct drm_dp_mst_branch *get_mst_branch_device_by_guid_helper(
 	struct drm_dp_mst_branch *found_mstb;
 	struct drm_dp_mst_port *port;
 
+	if (!mstb)
+		return NULL;
+
 	if (memcmp(mstb->guid, guid, 16) == 0)
 		return mstb;
 
 
 	list_for_each_entry(port, &mstb->ports, next) {
-		if (!port->mstb)
-			continue;
-
 		found_mstb = get_mst_branch_device_by_guid_helper(port->mstb, guid);
 
 		if (found_mstb)
@@ -2823,7 +2826,9 @@ static int process_single_tx_qlock(struct drm_dp_mst_topology_mgr *mgr,
 	ret = drm_dp_send_sideband_msg(mgr, up, chunk, idx);
 	if (ret) {
 		if (drm_debug_enabled(DRM_UT_DP)) {
-			struct drm_printer p = drm_debug_printer(DBG_PREFIX);
+			struct drm_printer p = drm_dbg_printer(mgr->dev,
+							       DRM_UT_DP,
+							       DBG_PREFIX);
 
 			drm_printf(&p, "sideband msg failed to send\n");
 			drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
@@ -2868,7 +2873,8 @@ static void drm_dp_queue_down_tx(struct drm_dp_mst_topology_mgr *mgr,
 	list_add_tail(&txmsg->next, &mgr->tx_msg_downq);
 
 	if (drm_debug_enabled(DRM_UT_DP)) {
-		struct drm_printer p = drm_debug_printer(DBG_PREFIX);
+		struct drm_printer p = drm_dbg_printer(mgr->dev, DRM_UT_DP,
+						       DBG_PREFIX);
 
 		drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
 	}
@@ -3578,38 +3584,54 @@ static int drm_dp_send_up_ack_reply(struct drm_dp_mst_topology_mgr *mgr,
  * value is in units of PBNs/(timeslots/1 MTP). This value can be used to
  * convert the number of PBNs required for a given stream to the number of
  * timeslots this stream requires in each MTP.
+ *
+ * Returns the BW / timeslot value in 20.12 fixed point format.
  */
-int drm_dp_get_vc_payload_bw(const struct drm_dp_mst_topology_mgr *mgr,
-			     int link_rate, int link_lane_count)
+fixed20_12 drm_dp_get_vc_payload_bw(const struct drm_dp_mst_topology_mgr *mgr,
+				    int link_rate, int link_lane_count)
 {
+	int ch_coding_efficiency =
+		drm_dp_bw_channel_coding_efficiency(drm_dp_is_uhbr_rate(link_rate));
+	fixed20_12 ret;
+
 	if (link_rate == 0 || link_lane_count == 0)
 		drm_dbg_kms(mgr->dev, "invalid link rate/lane count: (%d / %d)\n",
 			    link_rate, link_lane_count);
 
-	/* See DP v2.0 2.6.4.2, VCPayload_Bandwidth_for_OneTimeSlotPer_MTP_Allocation */
-	return link_rate * link_lane_count / 54000;
+	/* See DP v2.0 2.6.4.2, 2.7.6.3 VCPayload_Bandwidth_for_OneTimeSlotPer_MTP_Allocation */
+	ret.full = DIV_ROUND_DOWN_ULL(mul_u32_u32(link_rate * link_lane_count,
+						  ch_coding_efficiency),
+				      (1000000ULL * 8 * 5400) >> 12);
+
+	return ret;
 }
 EXPORT_SYMBOL(drm_dp_get_vc_payload_bw);
 
 /**
- * drm_dp_read_mst_cap() - check whether or not a sink supports MST
+ * drm_dp_read_mst_cap() - Read the sink's MST mode capability
  * @aux: The DP AUX channel to use
  * @dpcd: A cached copy of the DPCD capabilities for this sink
  *
- * Returns: %True if the sink supports MST, %false otherwise
+ * Returns: enum drm_dp_mst_mode to indicate MST mode capability
  */
-bool drm_dp_read_mst_cap(struct drm_dp_aux *aux,
-			 const u8 dpcd[DP_RECEIVER_CAP_SIZE])
+enum drm_dp_mst_mode drm_dp_read_mst_cap(struct drm_dp_aux *aux,
+					 const u8 dpcd[DP_RECEIVER_CAP_SIZE])
 {
 	u8 mstm_cap;
 
 	if (dpcd[DP_DPCD_REV] < DP_DPCD_REV_12)
-		return false;
+		return DRM_DP_SST;
 
 	if (drm_dp_dpcd_readb(aux, DP_MSTM_CAP, &mstm_cap) != 1)
-		return false;
+		return DRM_DP_SST;
+
+	if (mstm_cap & DP_MST_CAP)
+		return DRM_DP_MST;
 
-	return mstm_cap & DP_MST_CAP;
+	if (mstm_cap & DP_SINGLE_STREAM_SIDEBAND_MSG)
+		return DRM_DP_SST_SIDEBAND_MSG;
+
+	return DRM_DP_SST;
 }
 EXPORT_SYMBOL(drm_dp_read_mst_cap);
 
@@ -4197,7 +4219,7 @@ drm_dp_mst_detect_port(struct drm_connector *connector,
 	case DP_PEER_DEVICE_SST_SINK:
 		ret = connector_status_connected;
 		/* for logical ports - cache the EDID */
-		if (port->port_num >= DP_MST_LOGICAL_PORT_0 && !port->cached_edid)
+		if (drm_dp_mst_port_is_logical(port) && !port->cached_edid)
 			port->cached_edid = drm_edid_read_ddc(connector, &port->aux.ddc);
 		break;
 	case DP_PEER_DEVICE_DP_LEGACY_CONV:
@@ -4335,7 +4357,7 @@ int drm_dp_atomic_find_time_slots(struct drm_atomic_state *state,
 		}
 	}
 
-	req_slots = DIV_ROUND_UP(pbn, topology_state->pbn_div);
+	req_slots = DIV_ROUND_UP(dfixed_const(pbn), topology_state->pbn_div.full);
 
 	drm_dbg_atomic(mgr->dev, "[CONNECTOR:%d:%s] [MST PORT:%p] TU %d -> %d\n",
 		       port->connector->base.id, port->connector->name,
@@ -4718,35 +4740,36 @@ EXPORT_SYMBOL(drm_dp_check_act_status);
 
 /**
  * drm_dp_calc_pbn_mode() - Calculate the PBN for a mode.
- * @clock: dot clock for the mode
- * @bpp: bpp for the mode.
- * @dsc: DSC mode. If true, bpp has units of 1/16 of a bit per pixel
+ * @clock: dot clock
+ * @bpp: bpp as .4 binary fixed point
  *
  * This uses the formula in the spec to calculate the PBN value for a mode.
  */
-int drm_dp_calc_pbn_mode(int clock, int bpp, bool dsc)
+int drm_dp_calc_pbn_mode(int clock, int bpp)
 {
 	/*
-	 * margin 5300ppm + 300ppm ~ 0.6% as per spec, factor is 1.006
 	 * The unit of 54/64Mbytes/sec is an arbitrary unit chosen based on
 	 * common multiplier to render an integer PBN for all link rate/lane
 	 * counts combinations
 	 * calculate
-	 * peak_kbps *= (1006/1000)
-	 * peak_kbps *= (64/54)
-	 * peak_kbps *= 8    convert to bytes
-	 *
-	 * If the bpp is in units of 1/16, further divide by 16. Put this
-	 * factor in the numerator rather than the denominator to avoid
-	 * integer overflow
+	 * peak_kbps = clock * bpp / 16
+	 * peak_kbps *= SSC overhead / 1000000
+	 * peak_kbps /= 8    convert to Kbytes
+	 * peak_kBps *= (64/54) / 1000    convert to PBN
 	 */
+	/*
+	 * TODO: Use the actual link and mode parameters to calculate
+	 * the overhead. For now it's assumed that these are
+	 * 4 link lanes, 4096 hactive pixels, which don't add any
+	 * significant data padding overhead and that there is no DSC
+	 * or FEC overhead.
+	 */
+	int overhead = drm_dp_bw_overhead(4, 4096, 0, bpp,
+					  DRM_DP_BW_OVERHEAD_MST |
+					  DRM_DP_BW_OVERHEAD_SSC_REF_CLK);
 
-	if (dsc)
-		return DIV_ROUND_UP_ULL(mul_u32_u32(clock * (bpp / 16), 64 * 1006),
-					8 * 54 * 1000 * 1000);
-
-	return DIV_ROUND_UP_ULL(mul_u32_u32(clock * bpp, 64 * 1006),
-				8 * 54 * 1000 * 1000);
+	return DIV64_U64_ROUND_UP(mul_u32_u32(clock * bpp, 64 * overhead >> 4),
+				  1000000ULL * 8 * 54 * 1000);
 }
 EXPORT_SYMBOL(drm_dp_calc_pbn_mode);
 
@@ -4871,7 +4894,8 @@ void drm_dp_mst_dump_topology(struct seq_file *m,
 	state = to_drm_dp_mst_topology_state(mgr->base.state);
 	seq_printf(m, "\n*** Atomic state info ***\n");
 	seq_printf(m, "payload_mask: %x, max_payloads: %d, start_slot: %u, pbn_div: %d\n",
-		   state->payload_mask, mgr->max_payloads, state->start_slot, state->pbn_div);
+		   state->payload_mask, mgr->max_payloads, state->start_slot,
+		   dfixed_trunc(state->pbn_div));
 
 	seq_printf(m, "\n| idx | port | vcpi | slots | pbn | dsc | status |     sink name     |\n");
 	for (i = 0; i < mgr->max_payloads; i++) {
@@ -5136,13 +5160,67 @@ static bool drm_dp_mst_port_downstream_of_branch(struct drm_dp_mst_port *port,
 	return false;
 }
 
+static bool
+drm_dp_mst_port_downstream_of_parent_locked(struct drm_dp_mst_topology_mgr *mgr,
+					    struct drm_dp_mst_port *port,
+					    struct drm_dp_mst_port *parent)
+{
+	if (!mgr->mst_primary)
+		return false;
+
+	port = drm_dp_mst_topology_get_port_validated_locked(mgr->mst_primary,
+							     port);
+	if (!port)
+		return false;
+
+	if (!parent)
+		return true;
+
+	parent = drm_dp_mst_topology_get_port_validated_locked(mgr->mst_primary,
+							       parent);
+	if (!parent)
+		return false;
+
+	if (!parent->mstb)
+		return false;
+
+	return drm_dp_mst_port_downstream_of_branch(port, parent->mstb);
+}
+
+/**
+ * drm_dp_mst_port_downstream_of_parent - check if a port is downstream of a parent port
+ * @mgr: MST topology manager
+ * @port: the port being looked up
+ * @parent: the parent port
+ *
+ * The function returns %true if @port is downstream of @parent. If @parent is
+ * %NULL - denoting the root port - the function returns %true if @port is in
+ * @mgr's topology.
+ */
+bool
+drm_dp_mst_port_downstream_of_parent(struct drm_dp_mst_topology_mgr *mgr,
+				     struct drm_dp_mst_port *port,
+				     struct drm_dp_mst_port *parent)
+{
+	bool ret;
+
+	mutex_lock(&mgr->lock);
+	ret = drm_dp_mst_port_downstream_of_parent_locked(mgr, port, parent);
+	mutex_unlock(&mgr->lock);
+
+	return ret;
+}
+EXPORT_SYMBOL(drm_dp_mst_port_downstream_of_parent);
+
 static int
 drm_dp_mst_atomic_check_port_bw_limit(struct drm_dp_mst_port *port,
-				      struct drm_dp_mst_topology_state *state);
+				      struct drm_dp_mst_topology_state *state,
+				      struct drm_dp_mst_port **failing_port);
 
 static int
 drm_dp_mst_atomic_check_mstb_bw_limit(struct drm_dp_mst_branch *mstb,
-				      struct drm_dp_mst_topology_state *state)
+				      struct drm_dp_mst_topology_state *state,
+				      struct drm_dp_mst_port **failing_port)
 {
 	struct drm_dp_mst_atomic_payload *payload;
 	struct drm_dp_mst_port *port;
@@ -5171,7 +5249,7 @@ drm_dp_mst_atomic_check_mstb_bw_limit(struct drm_dp_mst_branch *mstb,
 		drm_dbg_atomic(mstb->mgr->dev, "[MSTB:%p] Checking bandwidth limits\n", mstb);
 
 	list_for_each_entry(port, &mstb->ports, next) {
-		ret = drm_dp_mst_atomic_check_port_bw_limit(port, state);
+		ret = drm_dp_mst_atomic_check_port_bw_limit(port, state, failing_port);
 		if (ret < 0)
 			return ret;
 
@@ -5183,7 +5261,8 @@ drm_dp_mst_atomic_check_mstb_bw_limit(struct drm_dp_mst_branch *mstb,
 
 static int
 drm_dp_mst_atomic_check_port_bw_limit(struct drm_dp_mst_port *port,
-				      struct drm_dp_mst_topology_state *state)
+				      struct drm_dp_mst_topology_state *state,
+				      struct drm_dp_mst_port **failing_port)
 {
 	struct drm_dp_mst_atomic_payload *payload;
 	int pbn_used = 0;
@@ -5204,13 +5283,15 @@ drm_dp_mst_atomic_check_port_bw_limit(struct drm_dp_mst_port *port,
 			drm_dbg_atomic(port->mgr->dev,
 				       "[MSTB:%p] [MST PORT:%p] no BW available for the port\n",
 				       port->parent, port);
+			*failing_port = port;
 			return -EINVAL;
 		}
 
 		pbn_used = payload->pbn;
 	} else {
 		pbn_used = drm_dp_mst_atomic_check_mstb_bw_limit(port->mstb,
-								 state);
+								 state,
+								 failing_port);
 		if (pbn_used <= 0)
 			return pbn_used;
 	}
@@ -5219,6 +5300,7 @@ drm_dp_mst_atomic_check_port_bw_limit(struct drm_dp_mst_port *port,
 		drm_dbg_atomic(port->mgr->dev,
 			       "[MSTB:%p] [MST PORT:%p] required PBN of %d exceeds port limit of %d\n",
 			       port->parent, port, pbn_used, port->full_pbn);
+		*failing_port = port;
 		return -ENOSPC;
 	}
 
@@ -5271,10 +5353,10 @@ drm_dp_mst_atomic_check_payload_alloc_limits(struct drm_dp_mst_topology_mgr *mgr
 	}
 
 	if (!payload_count)
-		mst_state->pbn_div = 0;
+		mst_state->pbn_div.full = dfixed_const(0);
 
 	drm_dbg_atomic(mgr->dev, "[MST MGR:%p] mst state %p TU pbn_div=%d avail=%d used=%d\n",
-		       mgr, mst_state, mst_state->pbn_div, avail_slots,
+		       mgr, mst_state, dfixed_trunc(mst_state->pbn_div), avail_slots,
 		       mst_state->total_avail_slots - avail_slots);
 
 	return 0;
@@ -5397,19 +5479,83 @@ int drm_dp_mst_atomic_enable_dsc(struct drm_atomic_state *state,
 EXPORT_SYMBOL(drm_dp_mst_atomic_enable_dsc);
 
 /**
+ * drm_dp_mst_atomic_check_mgr - Check the atomic state of an MST topology manager
+ * @state: The global atomic state
+ * @mgr: Manager to check
+ * @mst_state: The MST atomic state for @mgr
+ * @failing_port: Returns the port with a BW limitation
+ *
+ * Checks the given MST manager's topology state for an atomic update to ensure
+ * that it's valid. This includes checking whether there's enough bandwidth to
+ * support the new timeslot allocations in the atomic update.
+ *
+ * Any atomic drivers supporting DP MST must make sure to call this or
+ * the drm_dp_mst_atomic_check() function after checking the rest of their state
+ * in their &drm_mode_config_funcs.atomic_check() callback.
+ *
+ * See also:
+ * drm_dp_mst_atomic_check()
+ * drm_dp_atomic_find_time_slots()
+ * drm_dp_atomic_release_time_slots()
+ *
+ * Returns:
+ *   - 0 if the new state is valid
+ *   - %-ENOSPC, if the new state is invalid, because of BW limitation
+ *         @failing_port is set to:
+ *
+ *         - The non-root port where a BW limit check failed
+ *           with all the ports downstream of @failing_port passing
+ *           the BW limit check.
+ *           The returned port pointer is valid until at least
+ *           one payload downstream of it exists.
+ *         - %NULL if the BW limit check failed at the root port
+ *           with all the ports downstream of the root port passing
+ *           the BW limit check.
+ *
+ *   - %-EINVAL, if the new state is invalid, because the root port has
+ *     too many payloads.
+ */
+int drm_dp_mst_atomic_check_mgr(struct drm_atomic_state *state,
+				struct drm_dp_mst_topology_mgr *mgr,
+				struct drm_dp_mst_topology_state *mst_state,
+				struct drm_dp_mst_port **failing_port)
+{
+	int ret;
+
+	*failing_port = NULL;
+
+	if (!mgr->mst_state)
+		return 0;
+
+	mutex_lock(&mgr->lock);
+	ret = drm_dp_mst_atomic_check_mstb_bw_limit(mgr->mst_primary,
+						    mst_state,
+						    failing_port);
+	mutex_unlock(&mgr->lock);
+
+	if (ret < 0)
+		return ret;
+
+	return drm_dp_mst_atomic_check_payload_alloc_limits(mgr, mst_state);
+}
+EXPORT_SYMBOL(drm_dp_mst_atomic_check_mgr);
+
+/**
  * drm_dp_mst_atomic_check - Check that the new state of an MST topology in an
  * atomic update is valid
  * @state: Pointer to the new &struct drm_dp_mst_topology_state
  *
  * Checks the given topology state for an atomic update to ensure that it's
- * valid. This includes checking whether there's enough bandwidth to support
- * the new timeslot allocations in the atomic update.
+ * valid, calling drm_dp_mst_atomic_check_mgr() for all MST manager in the
+ * atomic state. This includes checking whether there's enough bandwidth to
+ * support the new timeslot allocations in the atomic update.
  *
  * Any atomic drivers supporting DP MST must make sure to call this after
  * checking the rest of their state in their
  * &drm_mode_config_funcs.atomic_check() callback.
  *
  * See also:
+ * drm_dp_mst_atomic_check_mgr()
  * drm_dp_atomic_find_time_slots()
  * drm_dp_atomic_release_time_slots()
  *
@@ -5424,21 +5570,11 @@ int drm_dp_mst_atomic_check(struct drm_atomic_state *state)
 	int i, ret = 0;
 
 	for_each_new_mst_mgr_in_state(state, mgr, mst_state, i) {
-		if (!mgr->mst_state)
-			continue;
+		struct drm_dp_mst_port *tmp_port;
 
-		ret = drm_dp_mst_atomic_check_payload_alloc_limits(mgr, mst_state);
+		ret = drm_dp_mst_atomic_check_mgr(state, mgr, mst_state, &tmp_port);
 		if (ret)
 			break;
-
-		mutex_lock(&mgr->lock);
-		ret = drm_dp_mst_atomic_check_mstb_bw_limit(mgr->mst_primary,
-							    mst_state);
-		mutex_unlock(&mgr->lock);
-		if (ret < 0)
-			break;
-		else
-			ret = 0;
 	}
 
 	return ret;
@@ -5803,7 +5939,6 @@ static int drm_dp_mst_register_i2c_bus(struct drm_dp_mst_port *port)
 	aux->ddc.algo_data = aux;
 	aux->ddc.retries = 3;
 
-	aux->ddc.class = I2C_CLASS_DDC;
 	aux->ddc.owner = THIS_MODULE;
 	/* FIXME: set the kdev of the port's connector as parent */
 	aux->ddc.dev.parent = parent_dev;
@@ -5848,7 +5983,7 @@ static bool drm_dp_mst_is_virtual_dpcd(struct drm_dp_mst_port *port)
 		return false;
 
 	/* Virtual DP Sink (Internal Display Panel) */
-	if (port->port_num >= 8)
+	if (drm_dp_mst_port_is_logical(port))
 		return true;
 
 	/* DP-to-HDMI Protocol Converter */
@@ -5876,6 +6011,22 @@ static bool drm_dp_mst_is_virtual_dpcd(struct drm_dp_mst_port *port)
 }
 
 /**
+ * drm_dp_mst_aux_for_parent() - Get the AUX device for an MST port's parent
+ * @port: MST port whose parent's AUX device is returned
+ *
+ * Return the AUX device for @port's parent or NULL if port's parent is the
+ * root port.
+ */
+struct drm_dp_aux *drm_dp_mst_aux_for_parent(struct drm_dp_mst_port *port)
+{
+	if (!port->parent || !port->parent->port_parent)
+		return NULL;
+
+	return &port->parent->port_parent->aux;
+}
+EXPORT_SYMBOL(drm_dp_mst_aux_for_parent);
+
+/**
  * drm_dp_mst_dsc_aux_for_port() - Find the correct aux for DSC
  * @port: The port to check. A leaf of the MST tree with an attached display.
  *
@@ -5894,6 +6045,7 @@ static bool drm_dp_mst_is_virtual_dpcd(struct drm_dp_mst_port *port)
 struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port)
 {
 	struct drm_dp_mst_port *immediate_upstream_port;
+	struct drm_dp_aux *immediate_upstream_aux;
 	struct drm_dp_mst_port *fec_port;
 	struct drm_dp_desc desc = {};
 	u8 endpoint_fec;
@@ -5958,21 +6110,25 @@ struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port)
 	 * - Port is on primary branch device
 	 * - Not a VGA adapter (DP_DWN_STRM_PORT_TYPE_ANALOG)
 	 */
-	if (drm_dp_read_desc(port->mgr->aux, &desc, true))
+	if (immediate_upstream_port)
+		immediate_upstream_aux = &immediate_upstream_port->aux;
+	else
+		immediate_upstream_aux = port->mgr->aux;
+
+	if (drm_dp_read_desc(immediate_upstream_aux, &desc, true))
 		return NULL;
 
-	if (drm_dp_has_quirk(&desc, DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD) &&
-	    port->mgr->dpcd[DP_DPCD_REV] >= DP_DPCD_REV_14 &&
-	    port->parent == port->mgr->mst_primary) {
+	if (drm_dp_has_quirk(&desc, DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD)) {
 		u8 dpcd_ext[DP_RECEIVER_CAP_SIZE];
 
-		if (drm_dp_read_dpcd_caps(port->mgr->aux, dpcd_ext) < 0)
+		if (drm_dp_read_dpcd_caps(immediate_upstream_aux, dpcd_ext) < 0)
 			return NULL;
 
-		if ((dpcd_ext[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT) &&
+		if (dpcd_ext[DP_DPCD_REV] >= DP_DPCD_REV_14 &&
+		    ((dpcd_ext[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT) &&
 		    ((dpcd_ext[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_TYPE_MASK)
-		     != DP_DWN_STRM_PORT_TYPE_ANALOG))
-			return port->mgr->aux;
+		     != DP_DWN_STRM_PORT_TYPE_ANALOG)))
+			return immediate_upstream_aux;
 	}
 
 	/*