Documentation: Add description of netdevsim traps

Signed-off-by: NIdo Schimmel <idosch@mellanox.com>
Acked-by: NJiri Pirko <jiri@mellanox.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Documentation/networking/devlink-trap-netdevsim.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+======================
+Devlink Trap netdevsim
+======================
+
+Driver-specific Traps
+=====================
+
+.. list-table:: List of Driver-specific Traps Registered by ``netdevsim``
+   :widths: 5 5 90
+
+   * - Name
+     - Type
+     - Description
+   * - ``fid_miss``
+     - ``exception``
+     - When a packet enters the device it is classified to a filtering
+       indentifier (FID) based on the ingress port and VLAN. This trap is used
+       to trap packets for which a FID could not be found

Documentation/networking/devlink-trap.rst

@@ -162,6 +162,17 @@ be added to the following table:
      - Traps packets that the device decided to drop because they could not be
        enqueued to a transmission queue which is full
 
+Driver-specific Packet Traps
+============================
+
+Device drivers can register driver-specific packet traps, but these must be
+clearly documented. Such traps can correspond to device-specific exceptions and
+help debug packet drops caused by these exceptions. The following list includes
+links to the description of driver-specific traps registered by various device
+drivers:
+
+  * :doc:`/devlink-trap-netdevsim`
+
 Generic Packet Trap Groups
 ==========================
 

Documentation/networking/index.rst

@@ -15,6 +15,7 @@ Contents:
    dsa/index
    devlink-info-versions
    devlink-trap
+   devlink-trap-netdevsim
    ieee802154
    kapi
    z8530book

drivers/net/netdevsim/dev.c

@@ -323,6 +323,9 @@ struct nsim_trap_data {
 	spinlock_t trap_lock;	/* Protects trap_items_arr */
 };
 
+/* All driver-specific traps must be documented in
+ * Documentation/networking/devlink-trap-netdevsim.rst
+ */
 enum {
 	NSIM_TRAP_ID_BASE = DEVLINK_TRAP_GENERIC_ID_MAX,
 	NSIM_TRAP_ID_FID_MISS,