U-Boot启动报错：已存在设备树却无法识别的原因排查

Alright, let's dig into why your custom Linux system on the Pynq Zynq board is hitting that frustrating device tree error—even though you've got devicetree.dtb sitting in your BOOT folder. Here are the most likely culprits to check:

1. U-Boot environment or config isn't pointing to the right DTB file #

U-Boot relies on either built-in config options or environment variables to know where to find the device tree.

• First, boot into U-Boot's command line (interrupt the boot process by pressing a key when prompted) and run printenv fdtfile. If this variable is set to something other than devicetree.dtb, that's the problem. Fix it with:

  setenv fdtfile devicetree.dtb
  saveenv
  

• If the fdtfile variable doesn't exist at all, check your U-Boot build config. Make sure CONFIG_DEFAULT_FDT_FILE is set to "devicetree.dtb" in your .config file before recompiling U-Boot.

2. The DTB file isn't in the right location on the BOOT partition #

Zynq's U-Boot expects the DTB to be in the root directory of the FAT32-formatted BOOT partition (usually the first partition on your SD card).

• Double-check that devicetree.dtb isn't tucked away in a subfolder.
• Verify the SD card is properly formatted as FAT32—some filesystems or corrupted partitions can prevent U-Boot from reading the file.
• Try re-copying the DTB file to the SD card to rule out a corrupted transfer.

3. Your U-Boot binary isn't configured to load an external DTB #

The error message explicitly mentions options like CONFIG_OF_EMBED or using u-boot-dtb.bin. This means your current u-boot.elf might be built to only look for an embedded device tree, not an external one.

• Option 1: Recompile U-Boot with CONFIG_OF_EMBED disabled and ensure options for external FDT loading (like CONFIG_OF_BOARD_SETUP) are enabled.
• Option 2: Create a u-boot-dtb.bin by embedding your devicetree.dtb directly into the U-Boot binary during compilation. This avoids relying on external file loading entirely.

4. FSBL isn't passing the DTB location to U-Boot #

If you're using a BOOT.BIN file (which packages FSBL, U-Boot, and optionally the DTB), make sure the DTB is included in the package and that FSBL is configured to load it into memory and pass its address to U-Boot.

• When building BOOT.BIN with tools like Xilinx SDK or bootgen, ensure you add the devicetree.dtb as a separate component and set the correct memory load address for it.
• If you're loading FSBL, U-Boot, and DTB separately via JTAG or SD card, confirm FSBL is loading the DTB to a memory address that U-Boot expects (check your U-Boot config for CONFIG_FDT_ADDR to find the expected address).

5. The DTB file itself is corrupted or incompatible #

Even if the file exists, it might be broken or not matched to your hardware/U-Boot version:

• Try replacing your custom devicetree.dtb with the official Pynq DTB file (from the Pynq repository) to see if the error goes away. This will rule out issues with your custom DTB.
• You can also validate the DTB by decompiling it:

  dtc -I dtb -O dts devicetree.dtb > devicetree.dts
  

  Open the resulting .dts file and check for syntax errors or missing nodes that U-Boot requires.

内容的提问来源于stack exchange，提问作者Leos313