如何从NAND中已安装的U-Boot自动设置环境？CONFIG_EXTRA_ENV_SETTINGS相关疑问

Let's tackle your questions one by one, since I've run into this exact scenario with NAND-based U-Boot setups before.

First, let's clear up the confusion: this macro defines default environment variables that are compiled directly into the U-Boot binary, not written automatically to your ubootenv NAND partition. Here's how it works at boot:

• U-Boot first tries to read the environment from your ubootenv partition. If that partition is valid (has a valid environment header/data), it uses those variables and ignores the compiled-in defaults.
• If the ubootenv partition is empty, corrupted, or this is the first boot, U-Boot falls back to the variables defined in CONFIG_EXTRA_ENV_SETTINGS—but it only loads them into memory for that boot session. It does not automatically write these defaults to the ubootenv partition, which is why you're not seeing them persist.

There are a few reliable ways to do this, depending on your use case (development vs mass production):

Option 1: Add auto-save logic to your board initialization code #

This is the most flexible approach for development or custom boards. You'll need to modify your board's post-relocation initialization code to check if the environment is valid, and save the defaults if it's not.

First, make sure your U-Boot config has the correct ubootenv partition settings (match your NAND layout):

#define CONFIG_ENV_OFFSET 0x400000  // Start address of your ubootenv partition
#define CONFIG_ENV_SIZE 0x100000    // Size of your ubootenv partition
#define CONFIG_ENV_IS_IN_NAND       // Tell U-Boot environment is in NAND

Then, in your board's board_init_r function (usually in board/<vendor>/<board>/board.c), add this logic after basic initialization:

#include <env.h>

void board_init_r(gd_t *gd, ulong dest_addr) {
    // ... existing board initialization code ...

    // Check if the environment partition is valid
    if (env_init() != 0) {
        // Environment is invalid/empty—load compiled defaults
        env_set_defaults(NULL, 0);
        // Save the defaults to the NAND ubootenv partition
        if (saveenv() == 0) {
            printf("Saved default environment to NAND ubootenv partition\n");
        } else {
            printf("Warning: Failed to save default environment!\n");
        }
    }

    // ... rest of your initialization code ...
}

Note: Depending on your U-Boot version, you might need to use env_valid() instead of checking env_init()'s return value—double-check the API docs for your specific U-Boot release.

Option 2: Pre-program the ubootenv partition during manufacturing #

For mass production, you can pre-generate an environment image and flash it alongside the U-Boot boot partition. Here's how:

1. Create a text file u-boot-env.txt with your desired variables:

bootargs=your_custom_boot_args_here
bootcmd=your_custom_boot_cmd_here

2. Generate a binary environment image using U-Boot's tools:
   • If you have fw_printenv/fw_setenv installed, configure a fw_env.config file matching your NAND layout, then run:

     fw_setenv -f -s u-boot-env.txt u-boot-env.bin
     

   • Alternatively, use mkimage (adjust architecture flags if needed):

     mkimage -A arm -O u-boot -T env -C none -a 0 -e 0 -n "U-Boot Environment" -d u-boot-env.txt u-boot-env.bin
     

3. Flash this u-boot-env.bin to the ubootenv partition (starting at 0x400000 in your layout) using your NAND flashing tool (like nandwrite in U-Boot or a factory programmer).

Option 3: Use CONFIG_AUTO_SAVE_ENV (if supported) #

Some newer U-Boot versions include a CONFIG_AUTO_SAVE_ENV config option. When enabled, U-Boot will automatically save the compiled-in default environment to the ubootenv partition if no valid environment is found. This is the simplest option if your U-Boot version supports it—just add the define to your config:

#define CONFIG_AUTO_SAVE_ENV

Note: This option isn't available in all U-Boot branches, so check your version's configs/<board>_defconfig or documentation first.

内容的提问来源于stack exchange，提问作者user157912