net: dsa: tag_rtl4_a: Implement Realtek 4 byte A tag

This implements the known parts of the Realtek 4 byte
tag protocol version 0xA, as found in the RTL8366RB
DSA switch.

It is designated as protocol version 0xA as a
different Realtek 4 byte tag format with protocol
version 0x9 is known to exist in the Realtek RTL8306
chips.

The tag and switch chip lacks public documentation, so
the tag format has been reverse-engineered from
packet dumps. As only ingress traffic has been available
for analysis an egress tag has not been possible to
develop (even using educated guesses about bit fields)
so this is as far as it gets. It is not known if the
switch even supports egress tagging.

Excessive attempts to figure out the egress tag format
was made. When nothing else worked, I just tried all bit
combinations with 0xannp where a is protocol and p is
port. I looped through all values several times trying
to get a response from ping, without any positive
result.

Using just these ingress tags however, the switch
functionality is vastly improved and the packets find
their way into the destination port without any
tricky VLAN configuration. On the D-Link DIR-685 the
LAN ports now come up and respond to ping without
any command line configuration so this is a real
improvement for users.

Egress packets need to be restricted to the proper
target ports using VLAN, which the RTL8366RB DSA
switch driver already sets up.

Cc: DENG Qingfang <dqfext@gmail.com>
Cc: Mauri Sandberg <sandberg@mailfence.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 0 deletions

diff --git a/net/dsa/Kconfig b/net/dsa/Kconfig
index d5bc6ac599ef..1f9b9b11008c 100644
--- a/net/dsa/Kconfig
+++ b/net/dsa/Kconfig
@@ -86,6 +86,13 @@ config NET_DSA_TAG_KSZ
 	  Say Y if you want to enable support for tagging frames for the
 	  Microchip 8795/9477/9893 families of switches.
 
+config NET_DSA_TAG_RTL4_A
+	tristate "Tag driver for Realtek 4 byte protocol A tags"
+	help
+	  Say Y or M if you want to enable support for tagging frames for the
+	  Realtek switches with 4 byte protocol A tags, sich as found in
+	  the Realtek RTL8366RB.
+
 config NET_DSA_TAG_OCELOT
 	tristate "Tag driver for Ocelot family of switches"
 	select PACKING