path: root/drm-dp-mst-fixes.patch

From 5118c9aeafecbfa5c2a49d757c882c6033828e7e Mon Sep 17 00:00:00 2001
From: Lyude Paul <lyude@redhat.com>
Date: Fri, 6 Mar 2020 18:46:19 -0500
Subject: [PATCH 1/4] drm/dp_mst: Rename drm_dp_mst_is_dp_mst_end_device() to
 be less redundant

It's already prefixed by dp_mst, so we don't really need to repeat
ourselves here. One of the changes I should have picked up originally
when reviewing MST DSC support.

There should be no functional changes here

Cc: Mikita Lipski <mikita.lipski@amd.com>
Cc: Sean Paul <seanpaul@google.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index cce0b1bba591..9188c53f5c96 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -1935,7 +1935,7 @@ static u8 drm_dp_calculate_rad(struct drm_dp_mst_port *port,
 	return parent_lct + 1;
 }
 
-static bool drm_dp_mst_is_dp_mst_end_device(u8 pdt, bool mcs)
+static bool drm_dp_mst_is_end_device(u8 pdt, bool mcs)
 {
 	switch (pdt) {
 	case DP_PEER_DEVICE_DP_LEGACY_CONV:
@@ -1965,13 +1965,13 @@ drm_dp_port_set_pdt(struct drm_dp_mst_port *port, u8 new_pdt,
 
 	/* Teardown the old pdt, if there is one */
 	if (port->pdt != DP_PEER_DEVICE_NONE) {
-		if (drm_dp_mst_is_dp_mst_end_device(port->pdt, port->mcs)) {
+		if (drm_dp_mst_is_end_device(port->pdt, port->mcs)) {
 			/*
 			 * If the new PDT would also have an i2c bus,
 			 * don't bother with reregistering it
 			 */
 			if (new_pdt != DP_PEER_DEVICE_NONE &&
-			    drm_dp_mst_is_dp_mst_end_device(new_pdt, new_mcs)) {
+			    drm_dp_mst_is_end_device(new_pdt, new_mcs)) {
 				port->pdt = new_pdt;
 				port->mcs = new_mcs;
 				return 0;
@@ -1991,7 +1991,7 @@ drm_dp_port_set_pdt(struct drm_dp_mst_port *port, u8 new_pdt,
 	port->mcs = new_mcs;
 
 	if (port->pdt != DP_PEER_DEVICE_NONE) {
-		if (drm_dp_mst_is_dp_mst_end_device(port->pdt, port->mcs)) {
+		if (drm_dp_mst_is_end_device(port->pdt, port->mcs)) {
 			/* add i2c over sideband */
 			ret = drm_dp_mst_register_i2c_bus(&port->aux);
 		} else {
@@ -2172,7 +2172,7 @@ drm_dp_mst_port_add_connector(struct drm_dp_mst_branch *mstb,
 	}
 
 	if (port->pdt != DP_PEER_DEVICE_NONE &&
-	    drm_dp_mst_is_dp_mst_end_device(port->pdt, port->mcs)) {
+	    drm_dp_mst_is_end_device(port->pdt, port->mcs)) {
 		port->cached_edid = drm_get_edid(port->connector,
 						 &port->aux.ddc);
 		drm_connector_set_tile_property(port->connector);
-- 
2.25.1

From 270862e1b736dc0e7c56a48fbb61b5ec76236982 Mon Sep 17 00:00:00 2001
From: Lyude Paul <lyude@redhat.com>
Date: Fri, 6 Mar 2020 18:46:20 -0500
Subject: [PATCH 2/4] drm/dp_mst: Use full_pbn instead of available_pbn for
 bandwidth checks

DisplayPort specifications are fun. For a while, it's been really
unclear to us what available_pbn actually does. There's a somewhat vague
explanation in the DisplayPort spec (starting from 1.2) that partially
explains it:

  The minimum payload bandwidth number supported by the path. Each node
  updates this number with its available payload bandwidth number if its
  payload bandwidth number is less than that in the Message Transaction
  reply.

So, it sounds like available_pbn represents the smallest link rate in
use between the source and the branch device. Cool, so full_pbn is just
the highest possible PBN that the branch device supports right?

Well, we assumed that for quite a while until Sean Paul noticed that on
some MST hubs, available_pbn will actually get set to 0 whenever there's
any active payloads on the respective branch device. This caused quite a
bit of confusion since clearing the payload ID table would end up fixing
the available_pbn value.

So, we just went with that until commit cd82d82cbc04 ("drm/dp_mst: Add
branch bandwidth validation to MST atomic check") started breaking
people's setups due to us getting erroneous available_pbn values. So, we
did some more digging and got confused until we finally looked at the
definition for full_pbn:

  The bandwidth of the link at the trained link rate and lane count
  between the DP Source device and the DP Sink device with no time slots
  allocated to VC Payloads, represented as a Payload Bandwidth Number. As
  with the Available_Payload_Bandwidth_Number, this number is determined
  by the link with the lowest lane count and link rate.

That's what we get for not reading specs closely enough, hehe. So, since
full_pbn is definitely what we want for doing bandwidth restriction
checks - let's start using that instead and ignore available_pbn
entirely.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Fixes: cd82d82cbc04 ("drm/dp_mst: Add branch bandwidth validation to MST atomic check")
Cc: Mikita Lipski <mikita.lipski@amd.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Sean Paul <sean@poorly.run>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 15 +++++++--------
 include/drm/drm_dp_mst_helper.h       |  4 ++--
 2 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 9188c53f5c96..7df7676b45c4 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2309,7 +2309,7 @@ drm_dp_mst_handle_link_address_port(struct drm_dp_mst_branch *mstb,
 								port);
 			}
 		} else {
-			port->available_pbn = 0;
+			port->full_pbn = 0;
 		}
 	}
 
@@ -2404,7 +2404,7 @@ drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb,
 		if (port->ddps) {
 			dowork = true;
 		} else {
-			port->available_pbn = 0;
+			port->full_pbn = 0;
 		}
 	}
 
@@ -2556,7 +2556,7 @@ static int drm_dp_check_and_send_link_address(struct drm_dp_mst_topology_mgr *mg
 		if (port->input || !port->ddps)
 			continue;
 
-		if (!port->available_pbn) {
+		if (!port->full_pbn) {
 			drm_modeset_lock(&mgr->base.lock, NULL);
 			drm_dp_send_enum_path_resources(mgr, mstb, port);
 			drm_modeset_unlock(&mgr->base.lock);
@@ -3002,8 +3002,7 @@ drm_dp_send_enum_path_resources(struct drm_dp_mst_topology_mgr *mgr,
 				      path_res->port_number,
 				      path_res->full_payload_bw_number,
 				      path_res->avail_payload_bw_number);
-			port->available_pbn =
-				path_res->avail_payload_bw_number;
+			port->full_pbn = path_res->full_payload_bw_number;
 			port->fec_capable = path_res->fec_capable;
 		}
 	}
@@ -3598,7 +3597,7 @@ drm_dp_mst_topology_mgr_invalidate_mstb(struct drm_dp_mst_branch *mstb)
 
 	list_for_each_entry(port, &mstb->ports, next) {
 		/* The PBN for each port will also need to be re-probed */
-		port->available_pbn = 0;
+		port->full_pbn = 0;
 
 		if (port->mstb)
 			drm_dp_mst_topology_mgr_invalidate_mstb(port->mstb);
@@ -4842,8 +4841,8 @@ int drm_dp_mst_atomic_check_bw_limit(struct drm_dp_mst_branch *branch,
 			if (drm_dp_mst_atomic_check_bw_limit(port->mstb, mst_state))
 				return -ENOSPC;
 
-		if (port->available_pbn > 0)
-			pbn_limit = port->available_pbn;
+		if (port->full_pbn > 0)
+			pbn_limit = port->full_pbn;
 	}
 	DRM_DEBUG_ATOMIC("[MST BRANCH:%p] branch has %d PBN available\n",
 			 branch, pbn_limit);
diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index bcb39da9adb4..41725d88d27e 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -81,7 +81,7 @@ struct drm_dp_vcpi {
  * &drm_dp_mst_topology_mgr.base.lock.
  * @num_sdp_stream_sinks: Number of stream sinks. Protected by
  * &drm_dp_mst_topology_mgr.base.lock.
- * @available_pbn: Available bandwidth for this port. Protected by
+ * @full_pbn: Max possible bandwidth for this port. Protected by
  * &drm_dp_mst_topology_mgr.base.lock.
  * @next: link to next port on this branch device
  * @aux: i2c aux transport to talk to device connected to this port, protected
@@ -126,7 +126,7 @@ struct drm_dp_mst_port {
 	u8 dpcd_rev;
 	u8 num_sdp_streams;
 	u8 num_sdp_stream_sinks;
-	uint16_t available_pbn;
+	uint16_t full_pbn;
 	struct list_head next;
 	/**
 	 * @mstb: the branch device connected to this port, if there is one.
-- 
2.25.1

From 6fceb6d9d9cdef2e26558f6b75700cc0f07a812c Mon Sep 17 00:00:00 2001
From: Lyude Paul <lyude@redhat.com>
Date: Fri, 6 Mar 2020 18:46:21 -0500
Subject: [PATCH 3/4] drm/dp_mst: Reprobe path resources in CSN handler

We used to punt off reprobing path resources to the link address probe
work, but now that we handle CSNs asynchronously from the driver's HPD
handling we can do whatever the heck we want from the CSN!

So, reprobe the path resources from drm_dp_mst_handle_conn_stat(). Also,
get rid of the path resource reprobing code in
drm_dp_check_and_send_link_address() since it's needlessly complicated
when we already reprobe path resources from
drm_dp_handle_link_address_port(). And finally, teach
drm_dp_send_enum_path_resources() to return 1 on PBN changes so we know
if we need to send another hotplug or not.

This fixes issues where we've indicated to userspace that a port has
just been connected, before we actually probed it's available PBN -
something that results in unexpected atomic check failures.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Fixes: cd82d82cbc04 ("drm/dp_mst: Add branch bandwidth validation to MST atomic check")
Cc: Mikita Lipski <mikita.lipski@amd.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Sean Paul <sean@poorly.run>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 48 ++++++++++++++-------------
 1 file changed, 25 insertions(+), 23 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 7df7676b45c4..112972031a84 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2302,12 +2302,16 @@ drm_dp_mst_handle_link_address_port(struct drm_dp_mst_branch *mstb,
 		mutex_unlock(&mgr->lock);
 	}
 
-	if (old_ddps != port->ddps) {
-		if (port->ddps) {
-			if (!port->input) {
-				drm_dp_send_enum_path_resources(mgr, mstb,
-								port);
-			}
+	/*
+	 * Reprobe PBN caps on both hotplug, and when re-probing the link
+	 * for our parent mstb
+	 */
+	if (old_ddps != port->ddps || !created) {
+		if (port->ddps && !port->input) {
+			ret = drm_dp_send_enum_path_resources(mgr, mstb,
+							      port);
+			if (ret == 1)
+				changed = true;
 		} else {
 			port->full_pbn = 0;
 		}
@@ -2401,11 +2405,10 @@ drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb,
 	port->ddps = conn_stat->displayport_device_plug_status;
 
 	if (old_ddps != port->ddps) {
-		if (port->ddps) {
-			dowork = true;
-		} else {
+		if (port->ddps && !port->input)
+			drm_dp_send_enum_path_resources(mgr, mstb, port);
+		else
 			port->full_pbn = 0;
-		}
 	}
 
 	new_pdt = port->input ? DP_PEER_DEVICE_NONE : conn_stat->peer_device_type;
@@ -2556,13 +2559,6 @@ static int drm_dp_check_and_send_link_address(struct drm_dp_mst_topology_mgr *mg
 		if (port->input || !port->ddps)
 			continue;
 
-		if (!port->full_pbn) {
-			drm_modeset_lock(&mgr->base.lock, NULL);
-			drm_dp_send_enum_path_resources(mgr, mstb, port);
-			drm_modeset_unlock(&mgr->base.lock);
-			changed = true;
-		}
-
 		if (port->mstb)
 			mstb_child = drm_dp_mst_topology_get_mstb_validated(
 			    mgr, port->mstb);
@@ -2990,6 +2986,7 @@ drm_dp_send_enum_path_resources(struct drm_dp_mst_topology_mgr *mgr,
 
 	ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
 	if (ret > 0) {
+		ret = 0;
 		path_res = &txmsg->reply.u.path_resources;
 
 		if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) {
@@ -3002,13 +2999,22 @@ drm_dp_send_enum_path_resources(struct drm_dp_mst_topology_mgr *mgr,
 				      path_res->port_number,
 				      path_res->full_payload_bw_number,
 				      path_res->avail_payload_bw_number);
+
+			/*
+			 * If something changed, make sure we send a
+			 * hotplug
+			 */
+			if (port->full_pbn != path_res->full_payload_bw_number ||
+			    port->fec_capable != path_res->fec_capable)
+				ret = 1;
+
 			port->full_pbn = path_res->full_payload_bw_number;
 			port->fec_capable = path_res->fec_capable;
 		}
 	}
 
 	kfree(txmsg);
-	return 0;
+	return ret;
 }
 
 static struct drm_dp_mst_port *drm_dp_get_last_connected_port_to_mstb(struct drm_dp_mst_branch *mstb)
@@ -3595,13 +3601,9 @@ drm_dp_mst_topology_mgr_invalidate_mstb(struct drm_dp_mst_branch *mstb)
 	/* The link address will need to be re-sent on resume */
 	mstb->link_address_sent = false;
 
-	list_for_each_entry(port, &mstb->ports, next) {
-		/* The PBN for each port will also need to be re-probed */
-		port->full_pbn = 0;
-
+	list_for_each_entry(port, &mstb->ports, next)
 		if (port->mstb)
 			drm_dp_mst_topology_mgr_invalidate_mstb(port->mstb);
-	}
 }
 
 /**
-- 
2.25.1

From 20c8afc6f3f18187517411323a125dfff3c014e7 Mon Sep 17 00:00:00 2001
From: Lyude Paul <lyude@redhat.com>
Date: Fri, 6 Mar 2020 18:46:22 -0500
Subject: [PATCH 4/4] drm/dp_mst: Rewrite and fix bandwidth limit checks
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Sigh, this is mostly my fault for not giving commit cd82d82cbc04
("drm/dp_mst: Add branch bandwidth validation to MST atomic check")
enough scrutiny during review. The way we're checking bandwidth
limitations here is mostly wrong:

For starters, drm_dp_mst_atomic_check_bw_limit() determines the
pbn_limit of a branch by simply scanning each port on the current branch
device, then uses the last non-zero full_pbn value that it finds. It
then counts the sum of the PBN used on each branch device for that
level, and compares against the full_pbn value it found before.

This is wrong because ports can and will have different PBN limitations
on many hubs, especially since a number of DisplayPort hubs out there
will be clever and only use the smallest link rate required for each
downstream sink - potentially giving every port a different full_pbn
value depending on what link rate it's trained at. This means with our
current code, which max PBN value we end up with is not well defined.

Additionally, we also need to remember when checking bandwidth
limitations that the top-most device in any MST topology is a branch
device, not a port. This means that the first level of a topology
doesn't technically have a full_pbn value that needs to be checked.
Instead, we should assume that so long as our VCPI allocations fit we're
within the bandwidth limitations of the primary MSTB.

We do however, want to check full_pbn on every port including those of
the primary MSTB. However, it's important to keep in mind that this
value represents the minimum link rate /between a port's sink or mstb,
and the mstb itself/. A quick diagram to explain:

                                MSTB #1
                               /       \
                              /         \
                           Port #1    Port #2
       full_pbn for Port #1 → |          | ← full_pbn for Port #2
                           Sink #1    MSTB #2
                                         |
                                       etc...

Note that in the above diagram, the combined PBN from all VCPI
allocations on said hub should not exceed the full_pbn value of port #2,
and the display configuration on sink #1 should not exceed the full_pbn
value of port #1. However, port #1 and port #2 can otherwise consume as
much bandwidth as they want so long as their VCPI allocations still fit.

And finally - our current bandwidth checking code also makes the mistake
of not checking whether something is an end device or not before trying
to traverse down it.

So, let's fix it by rewriting our bandwidth checking helpers. We split
the function into one part for handling branches which simply adds up
the total PBN on each branch and returns it, and one for checking each
port to ensure we're not going over its PBN limit. Phew.

This should fix regressions seen, where we erroneously reject display
configurations due to thinking they're going over our bandwidth limits
when they're not.

Changes since v1:
* Took an even closer look at how PBN limitations are supposed to be
  handled, and did some experimenting with Sean Paul. Ended up rewriting
  these helpers again, but this time they should actually be correct!

Signed-off-by: Lyude Paul <lyude@redhat.com>
Fixes: cd82d82cbc04 ("drm/dp_mst: Add branch bandwidth validation to MST atomic check")
Cc: Mikita Lipski <mikita.lipski@amd.com>
Cc: Sean Paul <seanpaul@google.com>
Cc: Hans de Goede <hdegoede@redhat.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 120 ++++++++++++++++++++------
 1 file changed, 94 insertions(+), 26 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 112972031a84..415bd0770eab 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -4830,41 +4830,103 @@ static bool drm_dp_mst_port_downstream_of_branch(struct drm_dp_mst_port *port,
 	return false;
 }
 
-static inline
-int drm_dp_mst_atomic_check_bw_limit(struct drm_dp_mst_branch *branch,
-				     struct drm_dp_mst_topology_state *mst_state)
+static int
+drm_dp_mst_atomic_check_port_bw_limit(struct drm_dp_mst_port *port,
+				      struct drm_dp_mst_topology_state *state);
+
+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_port *port;
 	struct drm_dp_vcpi_allocation *vcpi;
-	int pbn_limit = 0, pbn_used = 0;
+	struct drm_dp_mst_port *port;
+	int pbn_used = 0, ret;
+	bool found = false;
 
-	list_for_each_entry(port, &branch->ports, next) {
-		if (port->mstb)
-			if (drm_dp_mst_atomic_check_bw_limit(port->mstb, mst_state))
-				return -ENOSPC;
+	/* Check that we have at least one port in our state that's downstream
+	 * of this branch, otherwise we can skip this branch
+	 */
+	list_for_each_entry(vcpi, &state->vcpis, next) {
+		if (!vcpi->pbn ||
+		    !drm_dp_mst_port_downstream_of_branch(vcpi->port,
+							  mstb))
+			continue;
 
-		if (port->full_pbn > 0)
-			pbn_limit = port->full_pbn;
+		found = true;
+		break;
 	}
-	DRM_DEBUG_ATOMIC("[MST BRANCH:%p] branch has %d PBN available\n",
-			 branch, pbn_limit);
+	if (!found)
+		return 0;
 
-	list_for_each_entry(vcpi, &mst_state->vcpis, next) {
-		if (!vcpi->pbn)
-			continue;
+	if (mstb->port_parent)
+		DRM_DEBUG_ATOMIC("[MSTB:%p] [MST PORT:%p] Checking bandwidth limits on [MSTB:%p]\n",
+				 mstb->port_parent->parent, mstb->port_parent,
+				 mstb);
+	else
+		DRM_DEBUG_ATOMIC("[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);
+		if (ret < 0)
+			return ret;
 
-		if (drm_dp_mst_port_downstream_of_branch(vcpi->port, branch))
-			pbn_used += vcpi->pbn;
+		pbn_used += ret;
 	}
-	DRM_DEBUG_ATOMIC("[MST BRANCH:%p] branch used %d PBN\n",
-			 branch, pbn_used);
 
-	if (pbn_used > pbn_limit) {
-		DRM_DEBUG_ATOMIC("[MST BRANCH:%p] No available bandwidth\n",
-				 branch);
+	return pbn_used;
+}
+
+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_vcpi_allocation *vcpi;
+	int pbn_used = 0;
+
+	if (port->pdt == DP_PEER_DEVICE_NONE)
+		return 0;
+
+	if (drm_dp_mst_is_end_device(port->pdt, port->mcs)) {
+		bool found = false;
+
+		list_for_each_entry(vcpi, &state->vcpis, next) {
+			if (vcpi->port != port)
+				continue;
+			if (!vcpi->pbn)
+				return 0;
+
+			found = true;
+			break;
+		}
+		if (!found)
+			return 0;
+
+		/* This should never happen, as it means we tried to
+		 * set a mode before querying the full_pbn
+		 */
+		if (WARN_ON(!port->full_pbn))
+			return -EINVAL;
+
+		pbn_used = vcpi->pbn;
+	} else {
+		pbn_used = drm_dp_mst_atomic_check_mstb_bw_limit(port->mstb,
+								 state);
+		if (pbn_used <= 0)
+			return 0;
+	}
+
+	if (pbn_used > port->full_pbn) {
+		DRM_DEBUG_ATOMIC("[MSTB:%p] [MST PORT:%p] required PBN of %d exceeds port limit of %d\n",
+				 port->parent, port, pbn_used,
+				 port->full_pbn);
 		return -ENOSPC;
 	}
-	return 0;
+
+	DRM_DEBUG_ATOMIC("[MSTB:%p] [MST PORT:%p] uses %d out of %d PBN\n",
+			 port->parent, port, pbn_used, port->full_pbn);
+
+	return pbn_used;
 }
 
 static inline int
@@ -5062,9 +5124,15 @@ int drm_dp_mst_atomic_check(struct drm_atomic_state *state)
 		ret = drm_dp_mst_atomic_check_vcpi_alloc_limit(mgr, mst_state);
 		if (ret)
 			break;
-		ret = drm_dp_mst_atomic_check_bw_limit(mgr->mst_primary, mst_state);
-		if (ret)
+
+		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;
-- 
2.25.1