README.enetaddr 4.4 KB

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  1. ---------------------------------
  2. Ethernet Address (MAC) Handling
  3. ---------------------------------
  4. There are a variety of places in U-Boot where the MAC address is used, parsed,
  5. and stored. This document covers proper usage of each location and the moving
  6. of data between them.
  7. -----------
  8. Locations
  9. -----------
  10. Here are the places where MAC addresses might be stored:
  11. - board-specific location (eeprom, dedicated flash, ...)
  12. Note: only used when mandatory due to hardware design etc...
  13. - environment ("ethaddr", "eth1addr", ...) (see CONFIG_ETHADDR)
  14. Note: this is the preferred way to permanently store MAC addresses
  15. - ethernet data (struct eth_device -> enetaddr)
  16. Note: these are temporary copies of the MAC address which exist only
  17. after the respective init steps have run and only to make usage
  18. in other places easier (to avoid constant env lookup/parsing)
  19. - struct bd_info and/or device tree
  20. Note: these are temporary copies of the MAC address only for the
  21. purpose of passing this information to an OS kernel we are about
  22. to boot
  23. Correct flow of setting up the MAC address (summarized):
  24. 1. Read from hardware in initialize() function
  25. 2. Read from environment in net/eth.c after initialize()
  26. 3. Give priority to the value in the environment if a conflict
  27. 4. Program the address into hardware if the following conditions are met:
  28. a) The relevant driver has a 'write_addr' function
  29. b) The user hasn't set an 'ethmacskip' environment variable
  30. c) The address is valid (unicast, not all-zeros)
  31. Previous behavior had the MAC address always being programmed into hardware
  32. in the device's init() function.
  33. -------
  34. Usage
  35. -------
  36. If the hardware design mandates that the MAC address is stored in some special
  37. place (like EEPROM etc...), then the board specific init code (such as the
  38. board-specific misc_init_r() function) is responsible for locating the MAC
  39. address(es) and initializing the respective environment variable(s) from it.
  40. Note that this shall be done if, and only if, the environment does not already
  41. contain these environment variables, i.e. existing variable definitions must
  42. not be overwritten.
  43. During runtime, the ethernet layer will use the environment variables to sync
  44. the MAC addresses to the ethernet structures. All ethernet driver code should
  45. then only use the enetaddr member of the eth_device structure. This is done
  46. on every network command, so the ethernet copies will stay in sync.
  47. Any other code that wishes to access the MAC address should query the
  48. environment directly. The helper functions documented below should make
  49. working with this storage much smoother.
  50. ---------
  51. Helpers
  52. ---------
  53. To assist in the management of these layers, a few helper functions exist. You
  54. should use these rather than attempt to do any kind of parsing/manipulation
  55. yourself as many common errors have arisen in the past.
  56. * void eth_parse_enetaddr(const char *addr, uchar *enetaddr);
  57. Convert a string representation of a MAC address to the binary version.
  58. char *addr = "00:11:22:33:44:55";
  59. uchar enetaddr[6];
  60. eth_parse_enetaddr(addr, enetaddr);
  61. /* enetaddr now equals { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 } */
  62. * int eth_getenv_enetaddr(char *name, uchar *enetaddr);
  63. Look up an environment variable and convert the stored address. If the address
  64. is valid, then the function returns 1. Otherwise, the function returns 0. In
  65. all cases, the enetaddr memory is initialized. If the env var is not found,
  66. then it is set to all zeros. The common function is_valid_ether_addr() is used
  67. to determine address validity.
  68. uchar enetaddr[6];
  69. if (!eth_getenv_enetaddr("ethaddr", enetaddr)) {
  70. /* "ethaddr" is not set in the environment */
  71. ... try and setup "ethaddr" in the env ...
  72. }
  73. /* enetaddr is now set to the value stored in the ethaddr env var */
  74. * int eth_setenv_enetaddr(char *name, const uchar *enetaddr);
  75. Store the MAC address into the named environment variable. The return value is
  76. the same as the setenv() function.
  77. uchar enetaddr[6] = { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 };
  78. eth_setenv_enetaddr("ethaddr", enetaddr);
  79. /* the "ethaddr" env var should now be set to "00:11:22:33:44:55" */
  80. * the %pM format modifier
  81. The %pM format modifier can be used with any standard printf function to format
  82. the binary 6 byte array representation of a MAC address.
  83. uchar enetaddr[6] = { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 };
  84. printf("The MAC is %pM\n", enetaddr);
  85. char buf[20];
  86. sprintf(buf, "%pM", enetaddr);
  87. /* the buf variable is now set to "00:11:22:33:44:55" */