LXR uboot/doc/README.enetaddr

   1---------------------------------
   2 Ethernet Address (MAC) Handling
   3---------------------------------
   4
   5There are a variety of places in U-Boot where the MAC address is used, parsed,
   6and stored.  This document covers proper usage of each location and the moving
   7of data between them.
   8
   9-----------
  10 Locations
  11-----------
  12
  13Here are the places where MAC addresses might be stored:
  14
  15 - board-specific location (eeprom, dedicated flash, ...)
  16        Note: only used when mandatory due to hardware design etc...
  17
  18 - environment ("ethaddr", "eth1addr", ...)
  19        Note: this is the preferred way to permanently store MAC addresses
  20
  21 - ethernet data (struct eth_device -> enetaddr)
  22        Note: these are temporary copies of the MAC address which exist only
  23              after the respective init steps have run and only to make usage
  24              in other places easier (to avoid constant env lookup/parsing)
  25
  26 - struct bd_info and/or device tree
  27        Note: these are temporary copies of the MAC address only for the
  28              purpose of passing this information to an OS kernel we are about
  29              to boot
  30
  31Correct flow of setting up the MAC address (summarized):
  32
  331. Read from hardware in initialize() function
  342. Read from environment in net/eth.c after initialize()
  353. The environment variable will be compared to the driver initialized
  36   struct eth_device->enetaddr. If they differ, a warning is printed, and the
  37   environment variable will be used unchanged.
  38   If the environment variable is not set, it will be initialized from
  39   eth_device->enetaddr, and a warning will be printed.
  40   If both are invalid and CONFIG_NET_RANDOM_ETHADDR is defined, a random,
  41   locally-assigned MAC is written to eth_device->enetaddr.
  424. Program the address into hardware if the following conditions are met:
  43        a) The relevant driver has a 'write_addr' function
  44        b) The user hasn't set an 'ethmacskip' environment variable
  45        c) The address is valid (unicast, not all-zeros)
  46
  47Previous behavior had the MAC address always being programmed into hardware
  48in the device's init() function.
  49
  50-------
  51 Usage
  52-------
  53
  54If the hardware design mandates that the MAC address is stored in some special
  55place (like EEPROM etc...), then the board specific init code (such as the
  56board-specific misc_init_r() function) is responsible for locating the MAC
  57address(es) and initializing the respective environment variable(s) from it.
  58Note that this shall be done if, and only if, the environment does not already
  59contain these environment variables, i.e. existing variable definitions must
  60not be overwritten.
  61
  62During runtime, the ethernet layer will use the environment variables to sync
  63the MAC addresses to the ethernet structures.  All ethernet driver code should
  64then only use the enetaddr member of the eth_device structure.  This is done
  65on every network command, so the ethernet copies will stay in sync.
  66
  67Any other code that wishes to access the MAC address should query the
  68environment directly.  The helper functions documented below should make
  69working with this storage much smoother.
  70
  71---------
  72 Helpers
  73---------
  74
  75To assist in the management of these layers, a few helper functions exist.  You
  76should use these rather than attempt to do any kind of parsing/manipulation
  77yourself as many common errors have arisen in the past.
  78
  79        * void string_to_enetaddr(const char *addr, uchar *enetaddr);
  80
  81Convert a string representation of a MAC address to the binary version.
  82char *addr = "00:11:22:33:44:55";
  83uchar enetaddr[6];
  84string_to_enetaddr(addr, enetaddr);
  85/* enetaddr now equals { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 } */
  86
  87        * int eth_env_get_enetaddr(char *name, uchar *enetaddr);
  88
  89Look up an environment variable and convert the stored address.  If the address
  90is valid, then the function returns 1.  Otherwise, the function returns 0.  In
  91all cases, the enetaddr memory is initialized.  If the env var is not found,
  92then it is set to all zeros.  The common function is_valid_ethaddr() is used
  93to determine address validity.
  94uchar enetaddr[6];
  95if (!eth_env_get_enetaddr("ethaddr", enetaddr)) {
  96        /* "ethaddr" is not set in the environment */
  97        ... try and setup "ethaddr" in the env ...
  98}
  99/* enetaddr is now set to the value stored in the ethaddr env var */
 100
 101        * int eth_env_set_enetaddr(char *name, const uchar *enetaddr);
 102
 103Store the MAC address into the named environment variable.  The return value is
 104the same as the env_set() function.
 105uchar enetaddr[6] = { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 };
 106eth_env_set_enetaddr("ethaddr", enetaddr);
 107/* the "ethaddr" env var should now be set to "00:11:22:33:44:55" */
 108
 109        * the %pM format modifier
 110
 111The %pM format modifier can be used with any standard printf function to format
 112the binary 6 byte array representation of a MAC address.
 113uchar enetaddr[6] = { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 };
 114printf("The MAC is %pM\n", enetaddr);
 115
 116char buf[20];
 117sprintf(buf, "%pM", enetaddr);
 118/* the buf variable is now set to "00:11:22:33:44:55" */
 119