The Gianfar Ethernet Driver
  Sysfs File description
  
  Author: Andy Fleming <afleming@freescale.com>
  Updated: 2005-07-28
  
  SYSFS
  
  Several of the features of the gianfar driver are controlled
  through sysfs files.  These are:
  
  bd_stash:
  To stash RX Buffer Descriptors in the L2, echo 'on' or '1' to
  bd_stash, echo 'off' or '0' to disable
  
  rx_stash_len:
  To stash the first n bytes of the packet in L2, echo the number
  of bytes to buf_stash_len.  echo 0 to disable.
  
  WARNING: You could really screw these up if you set them too low or high!
  fifo_threshold:
  To change the number of bytes the controller needs in the
  fifo before it starts transmission, echo the number of bytes to 
  fifo_thresh.  Range should be 0-511.
  
  fifo_starve:
  When the FIFO has less than this many bytes during a transmit, it
  enters starve mode, and increases the priority of TX memory
  transactions.  To change, echo the number of bytes to
  fifo_starve.  Range should be 0-511.
  
  fifo_starve_off:
  Once in starve mode, the FIFO remains there until it has this
  many bytes.  To change, echo the number of bytes to
  fifo_starve_off.  Range should be 0-511.
  
  CHECKSUM OFFLOADING
  
  The eTSEC controller (first included in parts from late 2005 like
  the 8548) has the ability to perform TCP, UDP, and IP checksums
  in hardware.  The Linux kernel only offloads the TCP and UDP
  checksums (and always performs the pseudo header checksums), so
  the driver only supports checksumming for TCP/IP and UDP/IP
  packets.  Use ethtool to enable or disable this feature for RX
  and TX.
  
  VLAN
  
  In order to use VLAN, please consult Linux documentation on
  configuring VLANs.  The gianfar driver supports hardware insertion and
  extraction of VLAN headers, but not filtering.  Filtering will be
  done by the kernel.
  
  MULTICASTING
  
  The gianfar driver supports using the group hash table on the
  TSEC (and the extended hash table on the eTSEC) for multicast
  filtering.  On the eTSEC, the exact-match MAC registers are used
  before the hash tables.  See Linux documentation on how to join
  multicast groups.
  
  PADDING
  
  The gianfar driver supports padding received frames with 2 bytes
  to align the IP header to a 16-byte boundary, when supported by
  hardware.
  
  ETHTOOL
  
  The gianfar driver supports the use of ethtool for many
  configuration options.  You must run ethtool only on currently
  open interfaces.  See ethtool documentation for details.