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SubjectRe: [PATCH v3 net-next 19/24] net: dsa: sja1105: Add support for Spanning Tree Protocol
On Sat, Apr 13, 2019 at 04:28:17AM +0300, Vladimir Oltean wrote:
> While not explicitly documented as supported in UM10944, compliance with
> the STP states can be obtained by manipulating 3 settings at the
> (per-port) MAC config level: dynamic learning, inhibiting reception of
> regular traffic, and inhibiting transmission of regular traffic.
> In all these modes, transmission and reception of special BPDU frames
> from the stack is still enabled (not inhibited by the MAC-level
> settings).
> On ingress, BPDUs are classified by the MAC filter as link-local
> (01-80-C2-00-00-00) and forwarded to the CPU port. This mechanism works
> under all conditions (even without the custom 802.1Q tagging) because
> the switch hardware inserts the source port and switch ID into bytes 4
> and 5 of the MAC-filtered frames. Then the DSA .rcv handler needs to put
> back zeroes into the MAC address after decoding the source port
> information.
> On egress, BPDUs are transmitted using management routes from the xmit
> worker thread. Again this does not require switch tagging, as the switch
> port is programmed through SPI to hold a temporary (single-fire) route
> for a frame with the programmed destination MAC (01-80-C2-00-00-00).
> STP is activated using the following commands and was tested by
> connecting two front-panel ports together and noticing that switching
> loops were prevented (one port remains in the blocking state):
> $ ip link add name br0 type bridge stp_state 1 && ip link set br0 up
> $ for eth in $(ls /sys/devices/platform/soc/2100000.spi/spi_master/spi0/spi0.1/net/);
> do ip link set ${eth} master br0 && ip link set ${eth} up; done
> Signed-off-by: Vladimir Oltean <>

Reviewed-by: Andrew Lunn <>


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