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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()
353. Give priority to the value in the environment if a conflict
Ben Warrenecee9322010-04-26 11:11:46 -0700364. Program the address into hardware if the following conditions are met:
37 a) The relevant driver has a 'write_addr' function
38 b) The user hasn't set an 'ethmacskip' environment variable
39 c) The address is valid (unicast, not all-zeros)
Heiko Schocher8e64d6e2010-03-31 08:34:51 +020040
Ben Warrenecee9322010-04-26 11:11:46 -070041Previous behavior had the MAC address always being programmed into hardware
42in the device's init() function.
Heiko Schocher8e64d6e2010-03-31 08:34:51 +020043
Mike Frysinger6ff41372009-02-11 14:12:34 -050044-------
45 Usage
46-------
47
48If the hardware design mandates that the MAC address is stored in some special
49place (like EEPROM etc...), then the board specific init code (such as the
50board-specific misc_init_r() function) is responsible for locating the MAC
51address(es) and initializing the respective environment variable(s) from it.
52Note that this shall be done if, and only if, the environment does not already
53contain these environment variables, i.e. existing variable definitions must
54not be overwritten.
55
56During runtime, the ethernet layer will use the environment variables to sync
57the MAC addresses to the ethernet structures. All ethernet driver code should
58then only use the enetaddr member of the eth_device structure. This is done
59on every network command, so the ethernet copies will stay in sync.
60
61Any other code that wishes to access the MAC address should query the
62environment directly. The helper functions documented below should make
63working with this storage much smoother.
64
65---------
66 Helpers
67---------
68
69To assist in the management of these layers, a few helper functions exist. You
70should use these rather than attempt to do any kind of parsing/manipulation
71yourself as many common errors have arisen in the past.
72
73 * void eth_parse_enetaddr(const char *addr, uchar *enetaddr);
74
75Convert a string representation of a MAC address to the binary version.
76char *addr = "00:11:22:33:44:55";
77uchar enetaddr[6];
78eth_parse_enetaddr(addr, enetaddr);
79/* enetaddr now equals { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 } */
80
81 * int eth_getenv_enetaddr(char *name, uchar *enetaddr);
82
83Look up an environment variable and convert the stored address. If the address
84is valid, then the function returns 1. Otherwise, the function returns 0. In
85all cases, the enetaddr memory is initialized. If the env var is not found,
86then it is set to all zeros. The common function is_valid_ether_addr() is used
87to determine address validity.
88uchar enetaddr[6];
89if (!eth_getenv_enetaddr("ethaddr", enetaddr)) {
90 /* "ethaddr" is not set in the environment */
91 ... try and setup "ethaddr" in the env ...
92}
93/* enetaddr is now set to the value stored in the ethaddr env var */
94
95 * int eth_setenv_enetaddr(char *name, const uchar *enetaddr);
96
97Store the MAC address into the named environment variable. The return value is
98the same as the setenv() function.
99uchar enetaddr[6] = { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 };
100eth_setenv_enetaddr("ethaddr", enetaddr);
101/* the "ethaddr" env var should now be set to "00:11:22:33:44:55" */
102
103 * the %pM format modifier
104
105The %pM format modifier can be used with any standard printf function to format
106the binary 6 byte array representation of a MAC address.
107uchar enetaddr[6] = { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 };
108printf("The MAC is %pM\n", enetaddr);
109
110char buf[20];
111sprintf(buf, "%pM", enetaddr);
112/* the buf variable is now set to "00:11:22:33:44:55" */