net: ti: icssm-prueth: Add helper functions to configure and maintain FDB

net: ti: icssm-prueth: Add helper functions to configure and maintain FDB

Introduce helper functions to configure and maintain Forwarding
Database (FDB) tables to aid with the switch mode feature for PRU-ICSS
ports. The PRU-ICSS FDB is maintained such that it is always in sync with
the Linux bridge driver FDB.

The FDB is used by the driver to determine whether to flood a packet,
received from the user plane, to both ports or direct it to a specific port
using the flags in the FDB table entry.

The FDB is implemented in two main components: the Index table and the
MAC Address table. Adding, deleting, and maintaining entries are handled
by the PRUETH driver. There are two types of entries:

Dynamic: created from the received packets and are subject to aging.
Static: created by the user and these entries never age out.

8-bit hash value obtained using the source MAC address is used to identify
the index to the Index/Hash table. A bucket-based approach is used to
collate source MAC addresses with the same hash value. The Index/Hash table
holds the bucket index (16-bit value) and the number of entries in the
bucket with the same hash value (16-bit value). This table can hold up to
256 entries, with each entry consuming 4 bytes of memory. The bucket index
value points to the MAC address table indicating the start of MAC addresses
having the same hash values.

Each entry in the MAC Address table consists of:
1. 6 bytes of the MAC address,
2. 2-byte aging time, and
3. 1-byte each for port information and flags respectively.

When a new entry is added to the FDB, the hash value is calculated using an
XOR operation on the 6-byte MAC address. The result is used as an index
into the Hash/Index table to check if any entries exist. If no entries are
present, the first available empty slot in the MAC Address table is
allocated to insert this MAC address. If entries with the same hash value
are already present, the new MAC address entry is added to the MAC Address
table in such a way that it ensures all entries are grouped together and
sorted in ascending MAC address order. This approach helps efficiently
manage FDB entries.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Andrew F. Davis <afd@ti.com>
Signed-off-by: Basharath Hussain Khaja <basharath@couthit.com>
Signed-off-by: Parvathi Pudi <parvathi@couthit.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260130124559.1182780-2-parvathi@couthit.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>