Merge branch 'drm-fixes-mst' of git://people.freedesktop.org/~airlied/linux into drm-fixes

displayport multistream fixes from AMD.

* 'drm-fixes-mst' of git://people.freedesktop.org/~airlied/linux:
  drm/dp/mst: deallocate payload on port destruction
  drm/dp/mst: Reverse order of MST enable and clearing VC payload table.
  drm/dp/mst: move GUID storage from mgr, port to only mst branch
  drm/dp/mst: change MST detection scheme
  drm/dp/mst: Calculate MST PBN with 31.32 fixed point
  drm: Add drm_fixp_from_fraction and drm_fixp2int_ceil
  drm/mst: Add range check for max_payloads during init
  drm/mst: Don't ignore the MST PBN self-test result
  drm: fix missing reference counting decrease

3 files changed, 243 insertions, 114 deletions

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 6ed90a2437e5..8ae13de272c4 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -803,6 +803,18 @@ static struct drm_dp_mst_branch *drm_dp_add_mst_branch_device(u8 lct, u8 *rad)
         return mstb;
 }
 
+static void drm_dp_free_mst_port(struct kref *kref);
+
+static void drm_dp_free_mst_branch_device(struct kref *kref)
+{
+        struct drm_dp_mst_branch *mstb = container_of(kref, struct drm_dp_mst_branch, kref);
+        if (mstb->port_parent) {
+                if (list_empty(&mstb->port_parent->next))
+                        kref_put(&mstb->port_parent->kref, drm_dp_free_mst_port);
+        }
+        kfree(mstb);
+}
+
 static void drm_dp_destroy_mst_branch_device(struct kref *kref)
 {
         struct drm_dp_mst_branch *mstb = container_of(kref, struct drm_dp_mst_branch, kref);
@@ -810,6 +822,15 @@ static void drm_dp_destroy_mst_branch_device(struct kref *kref)
         bool wake_tx = false;
 
         /*
+         * init kref again to be used by ports to remove mst branch when it is
+         * not needed anymore
+         */
+        kref_init(kref);
+
+        if (mstb->port_parent && list_empty(&mstb->port_parent->next))
+                kref_get(&mstb->port_parent->kref);
+
+        /*
          * destroy all ports - don't need lock
          * as there are no more references to the mst branch
          * device at this point.
@@ -835,7 +856,8 @@ static void drm_dp_destroy_mst_branch_device(struct kref *kref)
 
         if (wake_tx)
                 wake_up(&mstb->mgr->tx_waitq);
-        kfree(mstb);
+
+        kref_put(kref, drm_dp_free_mst_branch_device);
 }
 
 static void drm_dp_put_mst_branch_device(struct drm_dp_mst_branch *mstb)
@@ -883,6 +905,7 @@ static void drm_dp_destroy_port(struct kref *kref)
                          * from an EDID retrieval */
 
                         mutex_lock(&mgr->destroy_connector_lock);
+                        kref_get(&port->parent->kref);
                         list_add(&port->next, &mgr->destroy_connector_list);
                         mutex_unlock(&mgr->destroy_connector_lock);
                         schedule_work(&mgr->destroy_connector_work);
@@ -1018,18 +1041,27 @@ static bool drm_dp_port_setup_pdt(struct drm_dp_mst_port *port)
         return send_link;
 }
 
-static void drm_dp_check_port_guid(struct drm_dp_mst_branch *mstb,
-                                   struct drm_dp_mst_port *port)
+static void drm_dp_check_mstb_guid(struct drm_dp_mst_branch *mstb, u8 *guid)
 {
         int ret;
-        if (port->dpcd_rev >= 0x12) {
-                port->guid_valid = drm_dp_validate_guid(mstb->mgr, port->guid);
-                if (!port->guid_valid) {
-                        ret = drm_dp_send_dpcd_write(mstb->mgr,
-                                                     port,
-                                                     DP_GUID,
-                                                     16, port->guid);
-                        port->guid_valid = true;
+
+        memcpy(mstb->guid, guid, 16);
+
+        if (!drm_dp_validate_guid(mstb->mgr, mstb->guid)) {
+                if (mstb->port_parent) {
+                        ret = drm_dp_send_dpcd_write(
+                                        mstb->mgr,
+                                        mstb->port_parent,
+                                        DP_GUID,
+                                        16,
+                                        mstb->guid);
+                } else {
+
+                        ret = drm_dp_dpcd_write(
+                                        mstb->mgr->aux,
+                                        DP_GUID,
+                                        mstb->guid,
+                                        16);
                 }
         }
 }
@@ -1086,7 +1118,6 @@ static void drm_dp_add_port(struct drm_dp_mst_branch *mstb,
         port->dpcd_rev = port_msg->dpcd_revision;
         port->num_sdp_streams = port_msg->num_sdp_streams;
         port->num_sdp_stream_sinks = port_msg->num_sdp_stream_sinks;
-        memcpy(port->guid, port_msg->peer_guid, 16);
 
         /* manage mstb port lists with mgr lock - take a reference
            for this list */
@@ -1099,11 +1130,9 @@ static void drm_dp_add_port(struct drm_dp_mst_branch *mstb,
 
         if (old_ddps != port->ddps) {
                 if (port->ddps) {
-                        drm_dp_check_port_guid(mstb, port);
                         if (!port->input)
                                 drm_dp_send_enum_path_resources(mstb->mgr, mstb, port);
                 } else {
-                        port->guid_valid = false;
                         port->available_pbn = 0;
                         }
         }
@@ -1130,13 +1159,11 @@ static void drm_dp_add_port(struct drm_dp_mst_branch *mstb,
                         drm_dp_put_port(port);
                         goto out;
                 }
-                if (port->port_num >= DP_MST_LOGICAL_PORT_0) {
-                        port->cached_edid = drm_get_edid(port->connector, &port->aux.ddc);
-                        drm_mode_connector_set_tile_property(port->connector);
-                }
+
+                drm_mode_connector_set_tile_property(port->connector);
+
                 (*mstb->mgr->cbs->register_connector)(port->connector);
         }
-
 out:
         /* put reference to this port */
         drm_dp_put_port(port);
@@ -1161,11 +1188,9 @@ static void drm_dp_update_port(struct drm_dp_mst_branch *mstb,
         port->ddps = conn_stat->displayport_device_plug_status;
 
         if (old_ddps != port->ddps) {
+                dowork = true;
                 if (port->ddps) {
-                        drm_dp_check_port_guid(mstb, port);
-                        dowork = true;
                 } else {
-                        port->guid_valid = false;
                         port->available_pbn = 0;
                 }
         }
@@ -1222,13 +1247,14 @@ 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 (memcmp(mstb->guid, guid, 16) == 0)
+                return mstb;
+
+
         list_for_each_entry(port, &mstb->ports, next) {
                 if (!port->mstb)
                         continue;
 
-                if (port->guid_valid && memcmp(port->guid, guid, 16) == 0)
-                        return port->mstb;
-
                 found_mstb = get_mst_branch_device_by_guid_helper(port->mstb, guid);
 
                 if (found_mstb)
@@ -1247,10 +1273,7 @@ static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device_by_guid(
         /* find the port by iterating down */
         mutex_lock(&mgr->lock);
 
-        if (mgr->guid_valid && memcmp(mgr->guid, guid, 16) == 0)
-                mstb = mgr->mst_primary;
-        else
-                mstb = get_mst_branch_device_by_guid_helper(mgr->mst_primary, guid);
+        mstb = get_mst_branch_device_by_guid_helper(mgr->mst_primary, guid);
 
         if (mstb)
                 kref_get(&mstb->kref);
@@ -1271,8 +1294,13 @@ static void drm_dp_check_and_send_link_address(struct drm_dp_mst_topology_mgr *m
                 if (port->input)
                         continue;
 
-                if (!port->ddps)
+                if (!port->ddps) {
+                        if (port->cached_edid) {
+                                kfree(port->cached_edid);
+                                port->cached_edid = NULL;
+                        }
                         continue;
+                }
 
                 if (!port->available_pbn)
                         drm_dp_send_enum_path_resources(mgr, mstb, port);
@@ -1283,6 +1311,12 @@ static void drm_dp_check_and_send_link_address(struct drm_dp_mst_topology_mgr *m
                                 drm_dp_check_and_send_link_address(mgr, mstb_child);
                                 drm_dp_put_mst_branch_device(mstb_child);
                         }
+                } else if (port->pdt == DP_PEER_DEVICE_SST_SINK ||
+                        port->pdt == DP_PEER_DEVICE_DP_LEGACY_CONV) {
+                        if (!port->cached_edid) {
+                                port->cached_edid =
+                                        drm_get_edid(port->connector, &port->aux.ddc);
+                        }
                 }
         }
 }
@@ -1302,6 +1336,8 @@ static void drm_dp_mst_link_probe_work(struct work_struct *work)
                 drm_dp_check_and_send_link_address(mgr, mstb);
                 drm_dp_put_mst_branch_device(mstb);
         }
+
+        (*mgr->cbs->hotplug)(mgr);
 }
 
 static bool drm_dp_validate_guid(struct drm_dp_mst_topology_mgr *mgr,
@@ -1555,10 +1591,12 @@ static void drm_dp_send_link_address(struct drm_dp_mst_topology_mgr *mgr,
                                        txmsg->reply.u.link_addr.ports[i].num_sdp_streams,
                                        txmsg->reply.u.link_addr.ports[i].num_sdp_stream_sinks);
                         }
+
+                        drm_dp_check_mstb_guid(mstb, txmsg->reply.u.link_addr.guid);
+
                         for (i = 0; i < txmsg->reply.u.link_addr.nports; i++) {
                                 drm_dp_add_port(mstb, mgr->dev, &txmsg->reply.u.link_addr.ports[i]);
                         }
-                        (*mgr->cbs->hotplug)(mgr);
                 }
         } else {
                 mstb->link_address_sent = false;
@@ -1602,6 +1640,37 @@ static int drm_dp_send_enum_path_resources(struct drm_dp_mst_topology_mgr *mgr,
         return 0;
 }
 
+static struct drm_dp_mst_port *drm_dp_get_last_connected_port_to_mstb(struct drm_dp_mst_branch *mstb)
+{
+        if (!mstb->port_parent)
+                return NULL;
+
+        if (mstb->port_parent->mstb != mstb)
+                return mstb->port_parent;
+
+        return drm_dp_get_last_connected_port_to_mstb(mstb->port_parent->parent);
+}
+
+static struct drm_dp_mst_branch *drm_dp_get_last_connected_port_and_mstb(struct drm_dp_mst_topology_mgr *mgr,
+                                                                         struct drm_dp_mst_branch *mstb,
+                                                                         int *port_num)
+{
+        struct drm_dp_mst_branch *rmstb = NULL;
+        struct drm_dp_mst_port *found_port;
+        mutex_lock(&mgr->lock);
+        if (mgr->mst_primary) {
+                found_port = drm_dp_get_last_connected_port_to_mstb(mstb);
+
+                if (found_port) {
+                        rmstb = found_port->parent;
+                        kref_get(&rmstb->kref);
+                        *port_num = found_port->port_num;
+                }
+        }
+        mutex_unlock(&mgr->lock);
+        return rmstb;
+}
+
 static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
                                    struct drm_dp_mst_port *port,
                                    int id,
@@ -1609,13 +1678,18 @@ static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
 {
         struct drm_dp_sideband_msg_tx *txmsg;
         struct drm_dp_mst_branch *mstb;
-        int len, ret;
+        int len, ret, port_num;
         u8 sinks[DRM_DP_MAX_SDP_STREAMS];
         int i;
 
+        port_num = port->port_num;
         mstb = drm_dp_get_validated_mstb_ref(mgr, port->parent);
-        if (!mstb)
-                return -EINVAL;
+        if (!mstb) {
+                mstb = drm_dp_get_last_connected_port_and_mstb(mgr, port->parent, &port_num);
+
+                if (!mstb)
+                        return -EINVAL;
+        }
 
         txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
         if (!txmsg) {
@@ -1627,7 +1701,7 @@ static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,
                 sinks[i] = i;
 
         txmsg->dst = mstb;
-        len = build_allocate_payload(txmsg, port->port_num,
+        len = build_allocate_payload(txmsg, port_num,
                                      id,
                                      pbn, port->num_sdp_streams, sinks);
 
@@ -1983,31 +2057,17 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms
                 mgr->mst_primary = mstb;
                 kref_get(&mgr->mst_primary->kref);
 
-                {
-                        struct drm_dp_payload reset_pay;
-                        reset_pay.start_slot = 0;
-                        reset_pay.num_slots = 0x3f;
-                        drm_dp_dpcd_write_payload(mgr, 0, &reset_pay);
-                }
-
                 ret = drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL,
-                                         DP_MST_EN | DP_UP_REQ_EN | DP_UPSTREAM_IS_SRC);
+                                                         DP_MST_EN | DP_UP_REQ_EN | DP_UPSTREAM_IS_SRC);
                 if (ret < 0) {
                         goto out_unlock;
                 }
 
-
-                /* sort out guid */
-                ret = drm_dp_dpcd_read(mgr->aux, DP_GUID, mgr->guid, 16);
-                if (ret != 16) {
-                        DRM_DEBUG_KMS("failed to read DP GUID %d\n", ret);
-                        goto out_unlock;
-                }
-
-                mgr->guid_valid = drm_dp_validate_guid(mgr, mgr->guid);
-                if (!mgr->guid_valid) {
-                        ret = drm_dp_dpcd_write(mgr->aux, DP_GUID, mgr->guid, 16);
-                        mgr->guid_valid = true;
+                {
+                        struct drm_dp_payload reset_pay;
+                        reset_pay.start_slot = 0;
+                        reset_pay.num_slots = 0x3f;
+                        drm_dp_dpcd_write_payload(mgr, 0, &reset_pay);
                 }
 
                 queue_work(system_long_wq, &mgr->work);
@@ -2231,9 +2291,8 @@ static int drm_dp_mst_handle_up_req(struct drm_dp_mst_topology_mgr *mgr)
                         }
 
                         drm_dp_update_port(mstb, &msg.u.conn_stat);
-                        DRM_DEBUG_KMS("Got CSN: pn: %d ldps:%d ddps: %d mcs: %d ip: %d pdt: %d\n", msg.u.conn_stat.port_number, msg.u.conn_stat.legacy_device_plug_status, msg.u.conn_stat.displayport_device_plug_status, msg.u.conn_stat.message_capability_status, msg.u.conn_stat.input_port, msg.u.conn_stat.peer_device_type);
-                        (*mgr->cbs->hotplug)(mgr);
 
+                        DRM_DEBUG_KMS("Got CSN: pn: %d ldps:%d ddps: %d mcs: %d ip: %d pdt: %d\n", msg.u.conn_stat.port_number, msg.u.conn_stat.legacy_device_plug_status, msg.u.conn_stat.displayport_device_plug_status, msg.u.conn_stat.message_capability_status, msg.u.conn_stat.input_port, msg.u.conn_stat.peer_device_type);
                 } else if (msg.req_type == DP_RESOURCE_STATUS_NOTIFY) {
                         drm_dp_send_up_ack_reply(mgr, mgr->mst_primary, msg.req_type, seqno, false);
                         if (!mstb)
@@ -2320,10 +2379,6 @@ enum drm_connector_status drm_dp_mst_detect_port(struct drm_connector *connector
 
         case DP_PEER_DEVICE_SST_SINK:
                 status = connector_status_connected;
-                /* for logical ports - cache the EDID */
-                if (port->port_num >= 8 && !port->cached_edid) {
-                        port->cached_edid = drm_get_edid(connector, &port->aux.ddc);
-                }
                 break;
         case DP_PEER_DEVICE_DP_LEGACY_CONV:
                 if (port->ldps)
@@ -2378,10 +2433,7 @@ struct edid *drm_dp_mst_get_edid(struct drm_connector *connector, struct drm_dp_
 
         if (port->cached_edid)
                 edid = drm_edid_duplicate(port->cached_edid);
-        else {
-                edid = drm_get_edid(connector, &port->aux.ddc);
-                drm_mode_connector_set_tile_property(connector);
-        }
+
         port->has_audio = drm_detect_monitor_audio(edid);
         drm_dp_put_port(port);
         return edid;
@@ -2446,6 +2498,7 @@ bool drm_dp_mst_allocate_vcpi(struct drm_dp_mst_topology_mgr *mgr, struct drm_dp
                 DRM_DEBUG_KMS("payload: vcpi %d already allocated for pbn %d - requested pbn %d\n", port->vcpi.vcpi, port->vcpi.pbn, pbn);
                 if (pbn == port->vcpi.pbn) {
                         *slots = port->vcpi.num_slots;
+                        drm_dp_put_port(port);
                         return true;
                 }
         }
@@ -2605,32 +2658,31 @@ EXPORT_SYMBOL(drm_dp_check_act_status);
  */
 int drm_dp_calc_pbn_mode(int clock, int bpp)
 {
-        fixed20_12 pix_bw;
-        fixed20_12 fbpp;
-        fixed20_12 result;
-        fixed20_12 margin, tmp;
-        u32 res;
-
-        pix_bw.full = dfixed_const(clock);
-        fbpp.full = dfixed_const(bpp);
-        tmp.full = dfixed_const(8);
-        fbpp.full = dfixed_div(fbpp, tmp);
-
-        result.full = dfixed_mul(pix_bw, fbpp);
-        margin.full = dfixed_const(54);
-        tmp.full = dfixed_const(64);
-        margin.full = dfixed_div(margin, tmp);
-        result.full = dfixed_div(result, margin);
-
-        margin.full = dfixed_const(1006);
-        tmp.full = dfixed_const(1000);
-        margin.full = dfixed_div(margin, tmp);
-        result.full = dfixed_mul(result, margin);
-
-        result.full = dfixed_div(result, tmp);
-        result.full = dfixed_ceil(result);
-        res = dfixed_trunc(result);
-        return res;
+        u64 kbps;
+        s64 peak_kbps;
+        u32 numerator;
+        u32 denominator;
+
+        kbps = clock * 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
+         */
+
+        numerator = 64 * 1006;
+        denominator = 54 * 8 * 1000 * 1000;
+
+        kbps *= numerator;
+        peak_kbps = drm_fixp_from_fraction(kbps, denominator);
+
+        return drm_fixp2int_ceil(peak_kbps);
 }
 EXPORT_SYMBOL(drm_dp_calc_pbn_mode);
 
@@ -2638,11 +2690,23 @@ static int test_calc_pbn_mode(void)
 {
         int ret;
         ret = drm_dp_calc_pbn_mode(154000, 30);
-        if (ret != 689)
+        if (ret != 689) {
+                DRM_ERROR("PBN calculation test failed - clock %d, bpp %d, expected PBN %d, actual PBN %d.\n",
+                                154000, 30, 689, ret);
                 return -EINVAL;
+        }
         ret = drm_dp_calc_pbn_mode(234000, 30);
-        if (ret != 1047)
+        if (ret != 1047) {
+                DRM_ERROR("PBN calculation test failed - clock %d, bpp %d, expected PBN %d, actual PBN %d.\n",
+                                234000, 30, 1047, ret);
                 return -EINVAL;
+        }
+        ret = drm_dp_calc_pbn_mode(297000, 24);
+        if (ret != 1063) {
+                DRM_ERROR("PBN calculation test failed - clock %d, bpp %d, expected PBN %d, actual PBN %d.\n",
+                                297000, 24, 1063, ret);
+                return -EINVAL;
+        }
         return 0;
 }
 
@@ -2783,6 +2847,13 @@ static void drm_dp_tx_work(struct work_struct *work)
         mutex_unlock(&mgr->qlock);
 }
 
+static void drm_dp_free_mst_port(struct kref *kref)
+{
+        struct drm_dp_mst_port *port = container_of(kref, struct drm_dp_mst_port, kref);
+        kref_put(&port->parent->kref, drm_dp_free_mst_branch_device);
+        kfree(port);
+}
+
 static void drm_dp_destroy_connector_work(struct work_struct *work)
 {
         struct drm_dp_mst_topology_mgr *mgr = container_of(work, struct drm_dp_mst_topology_mgr, destroy_connector_work);
@@ -2803,13 +2874,22 @@ static void drm_dp_destroy_connector_work(struct work_struct *work)
                 list_del(&port->next);
                 mutex_unlock(&mgr->destroy_connector_lock);
 
+                kref_init(&port->kref);
+                INIT_LIST_HEAD(&port->next);
+
                 mgr->cbs->destroy_connector(mgr, port->connector);
 
                 drm_dp_port_teardown_pdt(port, port->pdt);
 
-                if (!port->input && port->vcpi.vcpi > 0)
-                        drm_dp_mst_put_payload_id(mgr, port->vcpi.vcpi);
-                kfree(port);
+                if (!port->input && port->vcpi.vcpi > 0) {
+                        if (mgr->mst_state) {
+                                drm_dp_mst_reset_vcpi_slots(mgr, port);
+                                drm_dp_update_payload_part1(mgr);
+                                drm_dp_mst_put_payload_id(mgr, port->vcpi.vcpi);
+                        }
+                }
+
+                kref_put(&port->kref, drm_dp_free_mst_port);
                 send_hotplug = true;
         }
         if (send_hotplug)
@@ -2847,6 +2927,9 @@ int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr,
         mgr->max_dpcd_transaction_bytes = max_dpcd_transaction_bytes;
         mgr->max_payloads = max_payloads;
         mgr->conn_base_id = conn_base_id;
+        if (max_payloads + 1 > sizeof(mgr->payload_mask) * 8 ||
+            max_payloads + 1 > sizeof(mgr->vcpi_mask) * 8)
+                return -EINVAL;
         mgr->payloads = kcalloc(max_payloads, sizeof(struct drm_dp_payload), GFP_KERNEL);
         if (!mgr->payloads)
                 return -ENOMEM;
@@ -2854,7 +2937,9 @@ int drm_dp_mst_topology_mgr_init(struct drm_dp_mst_topology_mgr *mgr,
         if (!mgr->proposed_vcpis)
                 return -ENOMEM;
         set_bit(0, &mgr->payload_mask);
-        test_calc_pbn_mode();
+        if (test_calc_pbn_mode() < 0)
+                DRM_ERROR("MST PBN self-test failed\n");
+
         return 0;
 }
 EXPORT_SYMBOL(drm_dp_mst_topology_mgr_init);
diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index 24ab1787b771..fdb47051d549 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -44,8 +44,6 @@ struct drm_dp_vcpi {
 /**
  * struct drm_dp_mst_port - MST port
  * @kref: reference count for this port.
- * @guid_valid: for DP 1.2 devices if we have validated the GUID.
- * @guid: guid for DP 1.2 device on this port.
  * @port_num: port number
  * @input: if this port is an input port.
  * @mcs: message capability status - DP 1.2 spec.
@@ -70,10 +68,6 @@ struct drm_dp_vcpi {
 struct drm_dp_mst_port {
         struct kref kref;
 
-        /* if dpcd 1.2 device is on this port - its GUID info */
-        bool guid_valid;
-        u8 guid[16];
-
         u8 port_num;
         bool input;
         bool mcs;
@@ -110,10 +104,12 @@ struct drm_dp_mst_port {
  * @tx_slots: transmission slots for this device.
  * @last_seqno: last sequence number used to talk to this.
  * @link_address_sent: if a link address message has been sent to this device yet.
+ * @guid: guid for DP 1.2 branch device. port under this branch can be
+ * identified by port #.
  *
  * This structure represents an MST branch device, there is one
- * primary branch device at the root, along with any others connected
- * to downstream ports
+ * primary branch device at the root, along with any other branches connected
+ * to downstream port of parent branches.
  */
 struct drm_dp_mst_branch {
         struct kref kref;
@@ -132,6 +128,9 @@ struct drm_dp_mst_branch {
         struct drm_dp_sideband_msg_tx *tx_slots[2];
         int last_seqno;
         bool link_address_sent;
+
+        /* global unique identifier to identify branch devices */
+        u8 guid[16];
 };
 
 
@@ -406,11 +405,9 @@ struct drm_dp_payload {
  * @conn_base_id: DRM connector ID this mgr is connected to.
  * @down_rep_recv: msg receiver state for down replies.
  * @up_req_recv: msg receiver state for up requests.
- * @lock: protects mst state, primary, guid, dpcd.
+ * @lock: protects mst state, primary, dpcd.
  * @mst_state: if this manager is enabled for an MST capable port.
  * @mst_primary: pointer to the primary branch device.
- * @guid_valid: GUID valid for the primary branch device.
- * @guid: GUID for primary port.
  * @dpcd: cache of DPCD for primary port.
  * @pbn_div: PBN to slots divisor.
  *
@@ -432,13 +429,11 @@ struct drm_dp_mst_topology_mgr {
         struct drm_dp_sideband_msg_rx up_req_recv;
 
         /* pointer to info about the initial MST device */
-        struct mutex lock; /* protects mst_state + primary + guid + dpcd */
+        struct mutex lock; /* protects mst_state + primary + dpcd */
 
         bool mst_state;
         struct drm_dp_mst_branch *mst_primary;
-        /* primary MST device GUID */
-        bool guid_valid;
-        u8 guid[16];
+
         u8 dpcd[DP_RECEIVER_CAP_SIZE];
         u8 sink_count;
         int pbn_div;
diff --git a/include/drm/drm_fixed.h b/include/drm/drm_fixed.h
index d639049a613d..553210c02ee0 100644
--- a/include/drm/drm_fixed.h
+++ b/include/drm/drm_fixed.h
@@ -73,18 +73,28 @@ static inline u32 dfixed_div(fixed20_12 A, fixed20_12 B)
 #define DRM_FIXED_ONE           (1ULL << DRM_FIXED_POINT)
 #define DRM_FIXED_DECIMAL_MASK  (DRM_FIXED_ONE - 1)
 #define DRM_FIXED_DIGITS_MASK   (~DRM_FIXED_DECIMAL_MASK)
+#define DRM_FIXED_EPSILON       1LL
+#define DRM_FIXED_ALMOST_ONE    (DRM_FIXED_ONE - DRM_FIXED_EPSILON)
 
 static inline s64 drm_int2fixp(int a)
 {
         return ((s64)a) << DRM_FIXED_POINT;
 }
 
-static inline int drm_fixp2int(int64_t a)
+static inline int drm_fixp2int(s64 a)
 {
         return ((s64)a) >> DRM_FIXED_POINT;
 }
 
-static inline unsigned drm_fixp_msbset(int64_t a)
+static inline int drm_fixp2int_ceil(s64 a)
+{
+        if (a > 0)
+                return drm_fixp2int(a + DRM_FIXED_ALMOST_ONE);
+        else
+                return drm_fixp2int(a - DRM_FIXED_ALMOST_ONE);
+}
+
+static inline unsigned drm_fixp_msbset(s64 a)
 {
         unsigned shift, sign = (a >> 63) & 1;
 
@@ -136,6 +146,45 @@ static inline s64 drm_fixp_div(s64 a, s64 b)
         return result;
 }
 
+static inline s64 drm_fixp_from_fraction(s64 a, s64 b)
+{
+        s64 res;
+        bool a_neg = a < 0;
+        bool b_neg = b < 0;
+        u64 a_abs = a_neg ? -a : a;
+        u64 b_abs = b_neg ? -b : b;
+        u64 rem;
+
+        /* determine integer part */
+        u64 res_abs  = div64_u64_rem(a_abs, b_abs, &rem);
+
+        /* determine fractional part */
+        {
+                u32 i = DRM_FIXED_POINT;
+
+                do {
+                        rem <<= 1;
+                        res_abs <<= 1;
+                        if (rem >= b_abs) {
+                                res_abs |= 1;
+                                rem -= b_abs;
+                        }
+                } while (--i != 0);
+        }
+
+        /* round up LSB */
+        {
+                u64 summand = (rem << 1) >= b_abs;
+
+                res_abs += summand;
+        }
+
+        res = (s64) res_abs;
+        if (a_neg ^ b_neg)
+                res = -res;
+        return res;
+}
+
 static inline s64 drm_fixp_exp(s64 x)
 {
         s64 tolerance = div64_s64(DRM_FIXED_ONE, 1000000);