mctpd: add autonomous periodic discovery for point-to-point links

CHANGELOG.md

@@ -18,6 +18,11 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
    To support this, the minimum meson version has been bumped to 0.60,
    previously 0.59.
 
+3. `mctpd` now supports autonomous discovery on addressless point-to-point
+   physical links (Serial and USB, per Issue #174 Point 3) operating in Bus
+   Owner mode. Background periodic probing automatically discovers and assigns
+   EIDs once the interface is brought UP.
+
 ### Fixes
 
 1. In v2.6. we lost the peer initial MTU sematics, which gave us a safe minimum

conf/mctpd.conf

@@ -20,3 +20,17 @@ max_pool_size = 15
 # Bus Owner/bridge polling interval (ms) to check endpoint accessibility.
 # A value of 0 disables polling.
 endpoint_poll_ms = 0
+
+# Autonomous periodic discovery for point-to-point interfaces with no physical
+# addressing requirements (Serial and USB, per Issue #174 Point 3).
+# Default is false.
+auto_discovery = false
+
+# Periodic probing interval (ms) for point-to-point interfaces (100 - 60000 ms)
+probe_interval_ms = 1000
+
+# Example: enable autonomous discovery on serial point-to-point interfaces
+# [[interface]]
+# match = { phys-type = "serial" }
+# auto_discovery = true
+# probe_interval_ms = 500

docs/mctpd.md

@@ -434,6 +434,33 @@ Such periodic polling is common for all the briged endpoints among allocated
 pool space [`.PoolStart` - `.PoolEnd`] of the bridge.
 Polling could be provisioned to be disabled via setting the value as ```0```.
 
+#### `auto_discovery`: Autonomous discovery on point-to-point links
+
+* type: boolean
+* default: `false`
+
+Enables autonomous discovery (`Get Endpoint ID` 0x02) for point-to-point links
+without physical addressing requirements (Serial and USB, per Issue #174 Point 3)
+running in `bus-owner` mode.
+
+For addressless point-to-point transports (Serial and USB), `mctpd` periodically probes the link
+once brought `IFF_UP` until the endpoint responds and an EID is assigned. Probing begins
+automatically once the interface is brought administratively `IFF_UP` by system network
+configuration (e.g. via `systemd-networkd` or `udev`).
+
+Similar to bridged endpoint polling, collision prevention with external management
+tools (such as manual D-Bus `SetupEndpoint` calls) is not enforced by the daemon;
+applications must not concurrently configure endpoints on interfaces managed by
+autonomous discovery.
+
+#### `probe_interval_ms`: Periodic probing interval for point-to-point links
+
+* type: integer, in milliseconds
+* default: 1000
+
+Specifies the period between probe attempts on point-to-point links. Valid range is
+`100` ms to `60000` ms.
+
 ### `[[interface]]`: per-interface configuration
 
 The `[[interface]]` table allows configuration to be applied to specific
@@ -444,8 +471,10 @@ Matches are processed in the order they appear in the configuration file;
 the first `[[interface]]` section that matches is applied.
 
 Other content of the interface table is configuration to be applied. The
-only setting currently supported is `role`, to set mctpd's role as
-either bus-owner or endpoint on this interface.
+settings currently supported are:
+* `role`: sets mctpd's role as either `bus-owner` or `endpoint` on this interface.
+* `auto_discovery`: enables or disables autonomous periodic probing (`true` or `false`).
+* `probe_interval_ms`: periodic probing interval in milliseconds (100 - 60000 ms).
 
 For example, to apply a `bus-owner` role globally, with interface-specific
 `endpoint` roles for all i2c devices, and one particular (USB) device:
@@ -460,6 +489,12 @@ role = "endpoint"
 [[interface]]
 match = { path = "/devices/pci0000:00/0000:00:08.3/usb10/10-0:1.0" }
 role = "endpoint"
+
+# Enable auto-discovery on serial links with a faster probe interval:
+[[interface]]
+match = { phys-type = "serial" }
+auto_discovery = true
+probe_interval_ms = 500
 ```
 
 #### Match types