112 lines
4.4 KiB
Text
112 lines
4.4 KiB
Text
---------------------------------
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Ethernet Address (MAC) Handling
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---------------------------------
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There are a variety of places in U-Boot where the MAC address is used, parsed,
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and stored. This document covers proper usage of each location and the moving
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of data between them.
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-----------
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Locations
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-----------
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Here are the places where MAC addresses might be stored:
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- board-specific location (eeprom, dedicated flash, ...)
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Note: only used when mandatory due to hardware design etc...
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- environment ("ethaddr", "eth1addr", ...) (see CONFIG_ETHADDR)
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Note: this is the preferred way to permanently store MAC addresses
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- ethernet data (struct eth_device -> enetaddr)
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Note: these are temporary copies of the MAC address which exist only
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after the respective init steps have run and only to make usage
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in other places easier (to avoid constant env lookup/parsing)
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- struct bd_info and/or device tree
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Note: these are temporary copies of the MAC address only for the
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purpose of passing this information to an OS kernel we are about
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to boot
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Correct flow of setting up the MAC address (summarized):
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1. Read from hardware in initialize() function
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2. Read from environment in net/eth.c after initialize()
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3. Give priority to the value in the environment if a conflict
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4. Program the address into hardware if the following conditions are met:
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a) The relevant driver has a 'write_addr' function
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b) The user hasn't set an 'ethmacskip' environment variable
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c) The address is valid (unicast, not all-zeros)
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Previous behavior had the MAC address always being programmed into hardware
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in the device's init() function.
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-------
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Usage
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-------
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If the hardware design mandates that the MAC address is stored in some special
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place (like EEPROM etc...), then the board specific init code (such as the
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board-specific misc_init_r() function) is responsible for locating the MAC
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address(es) and initializing the respective environment variable(s) from it.
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Note that this shall be done if, and only if, the environment does not already
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contain these environment variables, i.e. existing variable definitions must
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not be overwritten.
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During runtime, the ethernet layer will use the environment variables to sync
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the MAC addresses to the ethernet structures. All ethernet driver code should
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then only use the enetaddr member of the eth_device structure. This is done
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on every network command, so the ethernet copies will stay in sync.
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Any other code that wishes to access the MAC address should query the
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environment directly. The helper functions documented below should make
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working with this storage much smoother.
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---------
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Helpers
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---------
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To assist in the management of these layers, a few helper functions exist. You
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should use these rather than attempt to do any kind of parsing/manipulation
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yourself as many common errors have arisen in the past.
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* void eth_parse_enetaddr(const char *addr, uchar *enetaddr);
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Convert a string representation of a MAC address to the binary version.
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char *addr = "00:11:22:33:44:55";
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uchar enetaddr[6];
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eth_parse_enetaddr(addr, enetaddr);
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/* enetaddr now equals { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 } */
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* int eth_getenv_enetaddr(char *name, uchar *enetaddr);
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Look up an environment variable and convert the stored address. If the address
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is valid, then the function returns 1. Otherwise, the function returns 0. In
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all cases, the enetaddr memory is initialized. If the env var is not found,
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then it is set to all zeros. The common function is_valid_ether_addr() is used
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to determine address validity.
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uchar enetaddr[6];
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if (!eth_getenv_enetaddr("ethaddr", enetaddr)) {
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/* "ethaddr" is not set in the environment */
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... try and setup "ethaddr" in the env ...
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}
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/* enetaddr is now set to the value stored in the ethaddr env var */
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* int eth_setenv_enetaddr(char *name, const uchar *enetaddr);
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Store the MAC address into the named environment variable. The return value is
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the same as the setenv() function.
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uchar enetaddr[6] = { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 };
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eth_setenv_enetaddr("ethaddr", enetaddr);
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/* the "ethaddr" env var should now be set to "00:11:22:33:44:55" */
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* the %pM format modifier
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The %pM format modifier can be used with any standard printf function to format
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the binary 6 byte array representation of a MAC address.
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uchar enetaddr[6] = { 0x00, 0x11, 0x22, 0x33, 0x44, 0x55 };
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printf("The MAC is %pM\n", enetaddr);
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char buf[20];
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sprintf(buf, "%pM", enetaddr);
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/* the buf variable is now set to "00:11:22:33:44:55" */
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