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Mike Frysinger6ff41372009-02-11 14:12:34 -05001---------------------------------
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", ...) (see CONFIG_ETHADDR)
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
Heiko Schocher8e64d6e2010-03-31 08:34:51 +020031Correct 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()
Rob Herringc88ef3c2012-04-14 18:06:49 +0000353. 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.
Ben Warrenecee9322010-04-26 11:11:46 -0700404. Program the address into hardware if the following conditions are met:
41 a) The relevant driver has a 'write_addr' function
42 b) The user hasn't set an 'ethmacskip' environment variable
43 c) The address is valid (unicast, not all-zeros)
Heiko Schocher8e64d6e2010-03-31 08:34:51 +020044
Ben Warrenecee9322010-04-26 11:11:46 -070045Previous behavior had the MAC address always being programmed into hardware
46in the device's init() function.
Heiko Schocher8e64d6e2010-03-31 08:34:51 +020047
Mike Frysinger6ff41372009-02-11 14:12:34 -050048-------
49 Usage
50-------
51
52If the hardware design mandates that the MAC address is stored in some special
53place (like EEPROM etc...), then the board specific init code (such as the
54board-specific misc_init_r() function) is responsible for locating the MAC
55address(es) and initializing the respective environment variable(s) from it.
56Note that this shall be done if, and only if, the environment does not already
57contain these environment variables, i.e. existing variable definitions must
58not be overwritten.
59
60During runtime, the ethernet layer will use the environment variables to sync
61the MAC addresses to the ethernet structures. All ethernet driver code should
62then only use the enetaddr member of the eth_device structure. This is done
63on every network command, so the ethernet copies will stay in sync.
64
65Any other code that wishes to access the MAC address should query the
66environment directly. The helper functions documented below should make
67working with this storage much smoother.
68
69---------
70 Helpers
71---------
72
73To assist in the management of these layers, a few helper functions exist. You
74should use these rather than attempt to do any kind of parsing/manipulation
75yourself as many common errors have arisen in the past.
76
77 * void eth_parse_enetaddr(const char *addr, uchar *enetaddr);
78
79Convert a string representation of a MAC address to the binary version.
80char *addr = "00:11:22:33:44:55";
81uchar enetaddr[6];
82eth_parse_enetaddr(addr, enetaddr);
83/* enetaddr now equals { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 } */
84
85 * int eth_getenv_enetaddr(char *name, uchar *enetaddr);
86
87Look up an environment variable and convert the stored address. If the address
88is valid, then the function returns 1. Otherwise, the function returns 0. In
89all cases, the enetaddr memory is initialized. If the env var is not found,
Joe Hershberger0adb5b72015-04-08 01:41:04 -050090then it is set to all zeros. The common function is_valid_ethaddr() is used
Mike Frysinger6ff41372009-02-11 14:12:34 -050091to determine address validity.
92uchar enetaddr[6];
93if (!eth_getenv_enetaddr("ethaddr", enetaddr)) {
94 /* "ethaddr" is not set in the environment */
95 ... try and setup "ethaddr" in the env ...
96}
97/* enetaddr is now set to the value stored in the ethaddr env var */
98
99 * int eth_setenv_enetaddr(char *name, const uchar *enetaddr);
100
101Store the MAC address into the named environment variable. The return value is
102the same as the setenv() function.
103uchar enetaddr[6] = { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 };
104eth_setenv_enetaddr("ethaddr", enetaddr);
105/* the "ethaddr" env var should now be set to "00:11:22:33:44:55" */
106
107 * the %pM format modifier
108
109The %pM format modifier can be used with any standard printf function to format
110the binary 6 byte array representation of a MAC address.
111uchar enetaddr[6] = { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 };
112printf("The MAC is %pM\n", enetaddr);
113
114char buf[20];
115sprintf(buf, "%pM", enetaddr);
116/* the buf variable is now set to "00:11:22:33:44:55" */