111 lines
5.2 KiB
Plaintext
111 lines
5.2 KiB
Plaintext
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ADM6996FC / ADM6996M switch chip driver
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1. General information
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This driver supports the FC and M models only. The ADM6996F and L are
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completely different chips.
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Support for the FC model is extremely limited at the moment. There is no VLAN
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support as of yet. The driver will not offer an swconfig interface for the FC
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chip.
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1.1 VLAN IDs
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It is possible to define 16 different VLANs. Every VLAN has an identifier, its
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VLAN ID. It is easiest if you use at most VLAN IDs 0-15. In that case, the
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swconfig based configuration is very straightforward. To define two VLANs with
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IDs 4 and 5, you can invoke, for example:
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# swconfig dev ethX vlan 4 set ports '0 1t 2 5t'
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# swconfig dev ethX vlan 5 set ports '0t 1t 5t'
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The swconfig framework will automatically invoke 'port Y set pvid Z' for every
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port that is an untagged member of VLAN Y, setting its Primary VLAN ID. In
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this example, ports 0 and 2 would get "pvid 4". The Primary VLAN ID of a port
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is the VLAN ID associated with untagged packets coming in on that port.
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But if you wish to use VLAN IDs outside the range 0-15, this automatic
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behaviour of the swconfig framework becomes a problem. The 16 VLANs that
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swconfig can configure on the ADM6996 also have a "vid" setting. By default,
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this is the same as the number of the VLAN entry, to make the simple behaviour
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above possible. To still support a VLAN with a VLAN ID higher than 15
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(presumably because you are in a network where such VLAN IDs are already in
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use), you can change the "vid" setting of the VLAN to anything in the range
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0-1023. But suppose you did the following:
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# swconfig dev ethX vlan 0 set vid 998
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# swconfig dev ethX vlan 0 set ports '0 2 5t'
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Now the swconfig framework will issue 'port 0 set pvid 0' and 'port 2 set pvid
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0'. But the "pvid" should be set to 998, so you are responsible for manually
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fixing this!
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1.2 VLAN filtering
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The switch is configured to apply source port filtering. This means that
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packets are only accepted when the port the packets came in on is a member of
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the VLAN the packet should go to.
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Only membership of a VLAN is tested, it does not matter whether it is a tagged
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or untagged membership.
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For untagged packets, the destination VLAN is the Primary VLAN ID of the
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incoming port. So if the PVID of a port is 0, but that port is not a member of
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the VLAN with ID 0, this means that untagged packets on that port are dropped.
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This can be used as a roundabout way of dropping untagged packets from a port,
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a mode often referred to as "Admit only tagged packets".
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1.3 Reset
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The two supported chip models do not have a sofware-initiated reset. When the
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driver is initialised, as well as when the 'reset' swconfig option is invoked,
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the driver will set those registers it knows about and supports to the correct
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default value. But there are a lot of registers in the chip that the driver
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does not support. If something changed those registers, invoking 'reset' or
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performing a warm reboot might still leave the chip in a "broken" state. Only
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a hardware reset will bring it back in the default state.
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2. Technical details on PHYs and the ADM6996
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From the viewpoint of the Linux kernel, it is common that an Ethernet adapter
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can be seen as a separate MAC entity and a separate PHY entity. The PHY entity
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can be queried and set through registers accessible via an MDIO bus. A PHY
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normally has a single address on that bus, in the range 0 through 31.
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The ADM6996 has special-purpose registers in the range of PHYs 0 through 10.
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Even though all these registers control a single ADM6996 chip, the Linux
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kernel treats this as 11 separate PHYs. The driver will bind to these
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addresses to prevent a different PHY driver from binding and corrupting these
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registers.
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What Linux sees as the PHY on address 0 is meant for the Ethernet MAC
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connected to the CPU port of the ADM6996 switch chip (port 5). This is the
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Ethernet MAC you will use to send and receive data through the switch.
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The PHYs at addresses 16 through 20 map to the PHYs on ports 0 through 4 of
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the switch chip. These can be accessed with the Generic PHY driver, as the
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registers have the common layout.
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If a second Ethernet MAC on your board is wired to the port 4 PHY, that MAC
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needs to bind to PHY address 20 for the port to work correctly.
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The ADM6996 switch driver will reset the ports 0 through 3 on startup and when
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'reset' is invoked. This could clash with a different PHY driver if the kernel
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binds a PHY driver to address 16 through 19.
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If Linux binds a PHY on addresses 1 through 10 to an Ethernet MAC, the ADM6996
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driver will simply always report a connected 100 Mbit/s full-duplex link for
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that PHY, and provide no other functionality. This is most likely not what you
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want. So if you see a message in your log
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ethX: PHY overlaps ADM6996, providing fixed PHY yy.
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This is most likely an indication that ethX will not work properly, and your
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kernel needs to be configured to attach a different PHY to that Ethernet MAC.
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Controlling the mapping between MACs and PHYs is usually done in platform- or
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board-specific fixup code. The ADM6996 driver has no influence over this.
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