linux-ksz8895

Microchip (formerly Micrel) KSZ8895 Linux device driver


Originally created to expand the single Ethernet port capabilities of a custom
OEM Ethernet router/gateway style device.  The device required multiple LAN
ports and a separate WAN port which is typical of these types of devices.  With
the KSZ8895, this can be achieved in two different ways:

  - Using two MACs – one connected to the 5-port switch for the LAN and the
    other connected to a 5th on-chip PHY for the WAN – the first 4 PHYs being
    attached to the switch
  - Using a single MAC and configuring VLANs on both the switch and Linux
    network interface to isolate LAN and WAN traffic.  The VLAN tags can also
    be removed on the egress of the 4 switch ports with attached PHYs.

Once upon a time, Micrel provided a driver for similar devices which they
claimed worked with earlier kernel builds.  However, it seemed to be poorly
designed, was not configurable without driver modification, and did not
function reliably.

With this driver, the switch and 5th on-chip PHY act as fake PHYs on a fake
MIIM (MDIO) bus.  This allows the switch to easily integrate with a MAC as if
it were a PHY while the driver controls the actual MIIM bus in the non-standard
SMI mode to monitor and control the switch and PHYs.  The SMI simply spreads
the switch register addresses across the register addresses of multiple PHY
addresses on the MIIM bus.

The driver should drop into the version 4.9 stable kernel without modification
as this is what it was most recently tested against.  However, it was
originally developed for 3.8; so it should also work reliably for everything
between if you give some of the API calls (which changed) a little massaging.