U-Boot writes incorrect CRC in env - environment-variables

Question

I'm using u-boot on raspberry pi 4, A/B booting from USB attached SSD, integrated with mender without yocto. Everything works fine except the env saving: initially configured to use MMC and offsets, fw_printenv complained about a bad CRC and output the default config instead. I changed the env saving to FAT files on the boot partition, and I'm now troubleshooting 2 issues:
uboot.env does not get written by issuing saveenv in the u-boot prompt
uboot-redund.env gets written but its CRC is incorrect.
I'm checking the CRC by issuing the fw_printenv command from linux. Its config file states:
/boot/u-boot/uboot-redund.env 0x0000 0x4000
U-Boot is compiled with 0x4000 as env size, and using hexdump to check the file shows a correct file with a length of 0x4000.
When booting up, u-boot outputs the following log over TTL serial:
U-Boot 2021.07-rc2-00246-gd64b3c608d-dirty (Jun 16 2021 - 12:16:24 +0200)
DRAM: 7.9 GiB
RPI 4 Model B (0xd03114)
MMC: mmcnr#7e300000: 1, emmc2#7e340000: 0
Loading Environment from FAT... In: serial
Out: vidconsole
Err: vidconsole
Net: eth0: ethernet#7d580000
PCIe BRCM: link up, 5.0 Gbps x1 (SSC)
starting USB...
Bus xhci_pci: Register 5000420 NbrPorts 5
Starting the controller
USB XHCI 1.00
scanning bus xhci_pci for devices... 3 USB Device(s) found
scanning usb for storage devices... 1 Storage Device(s) found
Hit any key to stop autoboot: 0
which shows that u-boot does load the env from FAT correctly.
How can I investigate further why u-boot does not write uboot.env, and why when it does write uboot-redund.env, writes it with a wrong CRC from fw_printenv's point of view?

Answer 1

env save
In function env_fat_save only one file is written. If CONFIG_SYS_REDUNDAND_ENVIRONMENT is defined, alternatively either file CONFIG_ENV_FAT_FILE_REDUND or file CONFIG_ENV_FAT_FILE is written.
You have to execute the command env save twice if you want to write both files.
Command env infoindicates which instance was written last via field env_valid:
=> env select FAT
Select Environment on FAT: OK
=> env info
env_valid = invalid
env_ready = true
env_use_default = false
=> env save
Saving Environment to FAT... OK
=> env info
env_valid = redundant
env_ready = true
env_use_default = false
=> env save
Saving Environment to FAT... OK
=> env info
env_valid = valid
env_ready = true
env_use_default = false
=>
fw_printenv
When using fw_printenv you must specify the configuration which matches your U-Boot build. By default file /etc/fw_env.config is used. You can pass the configuration file on the command line:
tools/env/fw_printenv -c fw_env.config
This is what your configuration file could look like:
uboot.env 0x0000 0x2000
uboot-redund.env 0x0000 0x2000
There is an example file in tools/env/fw_env.config explaining the available fields.