linux-phytec-ti

HACK: net: netcp: add special handling for broadcast/multicast

This is a hack to implement special packet processing for specific marked
packets. The intended use is:

  1. Ethernet interfaces are part of a bridge
  2. The switch is enabled (by default it is not) through sysfs command
  3. ALE is enabled through sysfs command
  4. Bridge forwarding is disabled  Bridge forwarding disabled via
     "ebtables -P FORWARD DROP

In this rather odd situation, the bridge will transmit multicast packets
(and broadcast) by sending one on each of the slaved interfaces.
This results in multiple packets through QoS, which is considered "bad".
To avoid this, multicast/broadcast packets can be marked via ebtables for
special processing in the NetCP PA module before the packets are queued
for transmission. Packets thus recognized are NOT marked for egress via a
specific slave port, and thus will be transmitted through all slave ports
by the ALE in NetCP switch.

To check if the interface is part of a bridge, a netcp_netdevice_event()
handler is added to mark the interface part of a bridge or not and is
used by the PA module. A new sysfs interface "mcast_filter" has been added
to allow user to configure two u32 values: a "match" value and a "mask".

As part of the pa tx hook, it checks if the interface is bridged. If true,
it checks if special processing is needed by looking at the skb->mark
field, it bitwise-ANDs the skb->mark value with the "mask" value and
then compares the result with the "match" value. If these do not match,
the mark is ignored and the packet is processed normally.

However, if the "match" value matches, then the low-order 8 bits of the
skb->mark field is used as a bitmask to determine whether the packet
should be dropped. If the packet would normally have been directed to
slave port 1, then bit 0 of skb->mark is checked; slave port 2 checks
bit 1, etc. If the bit is set, then the packet is enqueued; If the bit
is NOT set, the packet is silently dropped.

    An example...

  User enter
    echo "12345600 ffffff00" >
	/sys/devices/platform/soc/2620110.netcp/mcast_filter

The runtime configuration scripts execute this command:

 ebtables -A OUTPUT -d Multicast -j mark \
                --mark-set 0x12345601 --mark-target ACCEPT

When the bridge attempts to send multicast packet, it will send
one packet to each of the slave interfaces. The packet sent by the bridge
to slave interface eth0 (ethss slave port 1) will be passed to the NetCP
switch, and the ALE will send this packet on all slave ports. The packets
sent by the bridge to other slave interfaces (eth1, NetCP switch slave
port 2) will be silently dropped.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Reece R. Pollack <x0183204@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Tested-by: Wingman Kwok <w-kwok2@ti.com>