---------------------------------
   Ethernet Address (MAC) Handling
  ---------------------------------
  
  There are a variety of places in U-Boot where the MAC address is used, parsed,
  and stored.  This document covers proper usage of each location and the moving
  of data between them.
  
  -----------
   Locations
  -----------
  
  Here are the places where MAC addresses might be stored:
  
   - board-specific location (eeprom, dedicated flash, ...)
  	Note: only used when mandatory due to hardware design etc...

   - environment ("ethaddr", "eth1addr", ...)

  	Note: this is the preferred way to permanently store MAC addresses
  
   - ethernet data (struct eth_device -> enetaddr)
  	Note: these are temporary copies of the MAC address which exist only
  	      after the respective init steps have run and only to make usage
  	      in other places easier (to avoid constant env lookup/parsing)
  
   - struct bd_info and/or device tree
  	Note: these are temporary copies of the MAC address only for the
  	      purpose of passing this information to an OS kernel we are about
  	      to boot

  Correct flow of setting up the MAC address (summarized):
  
  1. Read from hardware in initialize() function
  2. Read from environment in net/eth.c after initialize()

  3. The environment variable will be compared to the driver initialized
     struct eth_device->enetaddr. If they differ, a warning is printed, and the
     environment variable will be used unchanged.
     If the environment variable is not set, it will be initialized from
     eth_device->enetaddr, and a warning will be printed.

     If both are invalid and CONFIG_NET_RANDOM_ETHADDR is defined, a random,
     locally-assigned MAC is written to eth_device->enetaddr.

  4. Program the address into hardware if the following conditions are met:
  	a) The relevant driver has a 'write_addr' function
  	b) The user hasn't set an 'ethmacskip' environment variable
  	c) The address is valid (unicast, not all-zeros)

  Previous behavior had the MAC address always being programmed into hardware
  in the device's init() function.

  -------
   Usage
  -------
  
  If the hardware design mandates that the MAC address is stored in some special
  place (like EEPROM etc...), then the board specific init code (such as the
  board-specific misc_init_r() function) is responsible for locating the MAC
  address(es) and initializing the respective environment variable(s) from it.
  Note that this shall be done if, and only if, the environment does not already
  contain these environment variables, i.e. existing variable definitions must
  not be overwritten.
  
  During runtime, the ethernet layer will use the environment variables to sync
  the MAC addresses to the ethernet structures.  All ethernet driver code should
  then only use the enetaddr member of the eth_device structure.  This is done
  on every network command, so the ethernet copies will stay in sync.
  
  Any other code that wishes to access the MAC address should query the
  environment directly.  The helper functions documented below should make
  working with this storage much smoother.
  
  ---------
   Helpers
  ---------
  
  To assist in the management of these layers, a few helper functions exist.  You
  should use these rather than attempt to do any kind of parsing/manipulation
  yourself as many common errors have arisen in the past.
  
  	* void eth_parse_enetaddr(const char *addr, uchar *enetaddr);
  
  Convert a string representation of a MAC address to the binary version.
  char *addr = "00:11:22:33:44:55";
  uchar enetaddr[6];
  eth_parse_enetaddr(addr, enetaddr);
  /* enetaddr now equals { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 } */

  	* int eth_env_get_enetaddr(char *name, uchar *enetaddr);

  
  Look up an environment variable and convert the stored address.  If the address
  is valid, then the function returns 1.  Otherwise, the function returns 0.  In
  all cases, the enetaddr memory is initialized.  If the env var is not found,

  then it is set to all zeros.  The common function is_valid_ethaddr() is used

  to determine address validity.
  uchar enetaddr[6];

  if (!eth_env_get_enetaddr("ethaddr", enetaddr)) {

  	/* "ethaddr" is not set in the environment */
  	... try and setup "ethaddr" in the env ...
  }
  /* enetaddr is now set to the value stored in the ethaddr env var */

  	* int eth_env_set_enetaddr(char *name, const uchar *enetaddr);

  
  Store the MAC address into the named environment variable.  The return value is

  the same as the env_set() function.

  uchar enetaddr[6] = { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 };

  eth_env_set_enetaddr("ethaddr", enetaddr);

  /* the "ethaddr" env var should now be set to "00:11:22:33:44:55" */
  
  	* the %pM format modifier
  
  The %pM format modifier can be used with any standard printf function to format
  the binary 6 byte array representation of a MAC address.
  uchar enetaddr[6] = { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 };
  printf("The MAC is %pM
  ", enetaddr);
  
  char buf[20];
  sprintf(buf, "%pM", enetaddr);
  /* the buf variable is now set to "00:11:22:33:44:55" */