From 0e2d9407659ddcb2e07e843afab386e28daeaea3 Mon Sep 17 00:00:00 2001
From: d00f <8052722+DrDoof@users.noreply.github.com>
Date: Tue, 13 Oct 2026 03:25:53 +0200
Subject: [PATCH] lldp: advertise system capabilities and the management
 address

Neighbours could not tell a bridge from a host and had no address to
reach us on. Add the System Capabilities TLV (bridge, enabled) and a
Management Address TLV with the IPv4 address, left out while the
address is still 0.0.0.0. Size the payload buffer for the frame it can
now hold: 64 bytes did not cover a 23 character hostname next to the
longer model names.
---
 rtl837x_lldp.c | 26 +++++++++++++++++++++++++-
 rtl837x_lldp.h | 12 ++++++++++++
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/rtl837x_lldp.c b/rtl837x_lldp.c
index 3eb644ea..590e15b2 100644
--- a/rtl837x_lldp.c
+++ b/rtl837x_lldp.c
@@ -42,7 +42,7 @@ struct lldp_pkt {
     struct rtl_tag rtl_tag;
     uint16_t ether_type;
 
-    uint8_t payload[64];
+    uint8_t payload[LLDP_MAX_PAYLOAD];
 };
 
 #define LLDP_O ((__xdata struct lldp_pkt *)&uip_buf[RTL_FRAME_DESC_SIZE])
@@ -90,6 +90,30 @@ void lldp_send(void) __banked __reentrant
     p += lldp_sysname(p);
     p += lldp_sysdesc(p);
 
+    //System Capabilities: supported, enabled
+    *p++ = LLDP_TYPE(LLDP_CAPABILITIES_TLV_TYPE);
+    *p++ = LLDP_CAPABILITIES_TLV_LENGTH;
+    *p++ = LLDP_CAPABILITY_BRIDGE >> 8;
+    *p++ = LLDP_CAPABILITY_BRIDGE & 0xff;
+    *p++ = LLDP_CAPABILITY_BRIDGE >> 8;
+    *p++ = LLDP_CAPABILITY_BRIDGE & 0xff;
+
+    //Management Address: IPv4
+    if (uip_hostaddr[0] | uip_hostaddr[1]) {
+        *p++ = LLDP_TYPE(LLDP_MGMT_ADDR_TLV_TYPE);
+        *p++ = LLDP_MGMT_ADDR_TLV_LENGTH;
+        *p++ = LLDP_MGMT_ADDR_STR_LENGTH;
+        *p++ = LLDP_MGMT_ADDR_SUBTYPE_IPV4;
+        memcpy(p, (__xdata uint8_t *)uip_hostaddr, sizeof(uip_ipaddr_t));
+        p += sizeof(uip_ipaddr_t);
+        *p++ = LLDP_MGMT_IF_NUMBERING_UNKNOWN;
+        *p++ = 0; //interface number
+        *p++ = 0;
+        *p++ = 0;
+        *p++ = 0;
+        *p++ = 0; //OID length
+    }
+
     // End of LLDPDU TLV
     *p++ = 0x00; //padding
     *p++ = 0x00; //padding
diff --git a/rtl837x_lldp.h b/rtl837x_lldp.h
index 4a48e121..8adc4a6f 100644
--- a/rtl837x_lldp.h
+++ b/rtl837x_lldp.h
@@ -27,6 +27,18 @@
 #define LLDP_SYSNAME_TLV_TYPE 5
 #define LLDP_SYSDESC_TLV_TYPE 6
 
+#define LLDP_CAPABILITIES_TLV_TYPE 7
+#define LLDP_CAPABILITIES_TLV_LENGTH 4
+#define LLDP_CAPABILITY_BRIDGE 0x0004
+
+#define LLDP_MGMT_ADDR_TLV_TYPE 8
+#define LLDP_MGMT_ADDR_TLV_LENGTH 12
+#define LLDP_MGMT_ADDR_STR_LENGTH 5
+#define LLDP_MGMT_ADDR_SUBTYPE_IPV4 1
+#define LLDP_MGMT_IF_NUMBERING_UNKNOWN 1
+
+#define LLDP_MAX_PAYLOAD 128
+
 void lldp_init(void) __banked;
 void lldp_tick(void) __banked;
 void lldp_send(void) __banked;