branch Attitude Adjustment

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