u-boot: Error: Can't overwrite "ethaddr"

When try to execute following command, It reports error as following:

--->8---

U-Boot> setenv ethaddr 4a:74:1f:75:31:56

## Error: Can't overwrite "ethaddr"

## Error inserting "ethaddr" variable, errno=1

---8<---

细致阅读README文件，有例如以下描写叙述：

－－－>8－－－

- Vendor Parameter Protection:





                U-Boot considers the values of the environment

                variables "serial#" (Board Serial Number) and

                "ethaddr" (Ethernet Address) to be parameters that

                are set once by the board vendor / manufacturer, and

                protects these variables from casual modification by

                the user. Once set, these variables are read-only,

                and write or delete attempts are rejected. You can

                change this behaviour:





                If CONFIG_ENV_OVERWRITE is #defined in your config

                file, the write protection for vendor parameters is

                completely disabled. Anybody can change or delete

                these parameters.





                Alternatively, if you #define _both_ CONFIG_ETHADDR

                _and_ CONFIG_OVERWRITE_ETHADDR_ONCE, a default

                Ethernet address is installed in the environment,

                which can be changed exactly ONCE by the user. [The

                serial# is unaffected by this, i. e. it remains

                read-only.]





                The same can be accomplished in a more flexible way

                for any variable by configuring the type of access

                to allow for those variables in the ".flags" variable

                or define CONFIG_ENV_FLAGS_LIST_STATIC.

－－－8<－－－

这样，最简单的方法是增加板相关文件：CONFIG_ENV_OVERWRITE 再次编译u-boot。写重启的问题得到解决。