Mctp bridge support

CHANGELOG.md

@@ -27,6 +27,11 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 5. When in endpoint mode, `mctpd` now handles to Set Endpoint ID messages,
    assigning an EID to local interfaces.
 
+6. `mctpd` now handles downstream MCTP bridges, which may request an EID
+   pool from their Set Endpoint ID response. It will attempt an EID allocation
+   from the dynamic range, and pass this to the bridge using a subsequent
+   Allocate Endpoint IDs command.
+
 ## [2.2] - 2025-07-28
 
 ### Fixed

docs/mctpd.md

@@ -126,7 +126,11 @@ busctl call au.com.codeconstruct.MCTP1 \
 
 Similar to SetupEndpoint, but will always assign an EID rather than querying for
 existing ones. Will return `new = false` when an endpoint is already known to
-`mctpd`.
+`mctpd`. If the endpoint is an MCTP bridge (indicated by requesting a pool size
+in its Set Endpoint ID response), this method attempts to allocate a contiguous
+range of EIDs for the bridge's downstream endpoints. If sufficient contiguous
+EIDs are not available within the dynamic allocation pool for the network, only
+the bridge's own EID will be assigned, and downstream EID allocation will fail.
 
 #### `.AssignEndpointStatic`: `ayy` → `yisb`
 
@@ -148,6 +152,14 @@ Like SetupEndpoint but will not assign EIDs, will only query endpoints for a
 current EID. The `new` return value is set to `false` for an already known
 endpoint, or `true` when an endpoint's EID is newly discovered.
 
+Because we are not issuing a Set Endpoint ID as part of the LearnEndpoint call,
+we do not have any details of the endpoint's bridge pool range. So,
+LearnEndpoint is unsuitable for use with bridge endpoints - it cannot provide
+the bridge with its own EID pool. `mctpd` will warn if the device type
+reports as a bridge.
+
+Bridge endpoints should be initialised with `AssignEndpoint` instead.
+
 ## Network objects: `/au/com/codeconstruct/networks/<net>`
 
 These objects represent MCTP networks which have been added use `mctp link`
@@ -215,6 +227,23 @@ busctl call au.com.codeconstruct.MCTP1 \
 
 Removes the MCTP endpoint from `mctpd`, and deletes routes and neighbour entries.
 
+### MCTP bridge interface: `au.com.codeconstruct.MCTP.Bridge1` interface
+
+MCTP endpoints that are set up as a bridge device (and therefore have an
+EID pool allocated to them, for downstream devices) also carry the
+`MCTP.Bridge1` interface. This provides details of the allocated EID pool, via
+two properties:
+
+### `.PoolStart`: `y`
+
+A constant property representing the first EID in the range allocated for
+downstream endpoints.
+
+### `.PoolEnd`: `y`
+
+A constant property representing the last EID in the range allocated for
+downstream endpoints.
+
 ## Configuration
 
 `mctpd` reads configuration data from a TOML file, typically `/etc/mctpd.conf`.

src/mctp-control-spec.h

@@ -183,6 +183,28 @@ struct mctp_ctrl_resp_resolve_endpoint_id {
 	// ... uint8_t physical_address[N]
 } __attribute__((__packed__));
 
+typedef enum {
+	mctp_ctrl_cmd_allocate_eids_alloc_eids = 0,
+	mctp_ctrl_cmd_allocate_eids_force_alloc = 1,
+	mctp_ctrl_cmd_allocate_eids_get_alloc_info = 2,
+	mctp_ctrl_cmd_allocate_eids_reserved = 3
+} mctp_ctrl_cmd_allocate_eids_op;
+
+struct mctp_ctrl_cmd_allocate_eids {
+	struct mctp_ctrl_msg_hdr ctrl_hdr;
+	uint8_t alloc_eid_op;
+	uint8_t pool_size;
+	uint8_t start_eid;
+} __attribute__((__packed__));
+
+struct mctp_ctrl_resp_allocate_eids {
+	struct mctp_ctrl_msg_hdr ctrl_hdr;
+	uint8_t completion_code;
+	uint8_t status;
+	uint8_t eid_pool_size;
+	uint8_t eid_set;
+} __attribute__((__packed__));
+
 #define MCTP_CTRL_HDR_MSG_TYPE 0
 #define MCTP_CTRL_HDR_FLAG_REQUEST (1 << 7)
 #define MCTP_CTRL_HDR_FLAG_DGRAM (1 << 6)
@@ -257,6 +279,28 @@ struct mctp_ctrl_resp_resolve_endpoint_id {
 #define MCTP_SET_EID_ACCEPTED 0x0
 #define MCTP_SET_EID_REJECTED 0x1
 
+/* MCTP Get Endpoint ID request and response fields
+ * See DSP0236 v1.3.0 Table 15.
+ */
+#define MCTP_GET_EID_EP_TYPE_SHIFT 4
+#define MCTP_GET_EID_EP_TYPE_MASK 0x03
+#define GET_MCTP_GET_EID_EP_TYPE(field) \
+	(((field) >> MCTP_GET_EID_EP_TYPE_SHIFT) & MCTP_GET_EID_EP_TYPE_MASK)
+#define MCTP_GET_EID_EP_TYPE_EP 0
+#define MCTP_GET_EID_EP_TYPE_BRIDGE 1
+
+#define MCTP_GET_EID_EID_TYPE_SHIFT 0
+#define MCTP_GET_EID_EID_TYPE_MASK 0x03
+#define GET_MCTP_GET_EID_EID_TYPE(field) \
+	(((field) >> MCTP_GET_EID_EID_TYPE_SHIFT) & MCTP_GET_EID_EID_TYPE_MASK)
+#define MCTP_GET_EID_EID_TYPE_DYNAMIC 0
+/* Static EID is supported, may or may not match current */
+#define MCTP_GET_EID_EID_TYPE_STATIC 1
+/* Current eid is the same as static */
+#define MCTP_GET_EID_EID_TYPE_STATIC_SAME 2
+/* Current eid is different from static */
+#define MCTP_GET_EID_EID_TYPE_STATIC_DIFFERENT 3
+
 #define MCTP_EID_ALLOCATION_STATUS_SHIFT 0x0
 #define MCTP_EID_ALLOCATION_STATUS_MASK 0x3
 #define SET_MCTP_EID_ALLOCATION_STATUS(status)        \