The sja1105 switch family has a feature called "cascade ports" which can
be used in topologies where multiple SJA1105/SJA1110 switches are daisy
chained. Upstream switches set this bit for the DSA link towards the
downstream switches. This is used when the upstream switch receives a
control packet (PTP, STP) from a downstream switch, because if the
source port for a control packet is marked as a cascade port, then the
source port, switch ID and RX timestamp will not be taken again on the
upstream switch, it is assumed that this has already been done by the
downstream switch (the leaf port in the tree) and that the CPU has
everything it needs to decode the information from this packet.
We need to distinguish between an upstream-facing DSA link and a
downstream-facing DSA link, because the upstream-facing DSA links are
"host ports" for the SJA1105/SJA1110 switches, and the downstream-facing
DSA links are "cascade ports".
Note that SJA1105 supports a single cascade port, so only daisy chain
topologies work. With SJA1110, there can be more complex topologies such
as:
eth0
|
host port
|
sw0p0 sw0p1 sw0p2 sw0p3 sw0p4
| | | |
cascade cascade user user
port port port port
| |
| |
| |
| host
| port
| |
| sw1p0 sw1p1 sw1p2 sw1p3 sw1p4
| | | | |
| user user user user
host port port port port
port
|
sw2p0 sw2p1 sw2p2 sw2p3 sw2p4
| | | |
user user user user
port port port port
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
30a100e60c