Re: Unexpected RPi5 Behavior with Saved U-Boot Environment

[Mauro Salvini <m.salvini@koansoftware.com>]

On 21/04/25 12:15, Peter Robinson wrote:
> Hi Mauro,
> 
>>> We recently started using U-Boot on various Raspberry Pi 5 boards
>>> with different hardware configurations.
>>>
>>> While testing, Simon noticed unusual boot failures, such as the kernel
>>> failing to boot with no output or U-Boot reporting:
>>> "ERROR: Did not find a cmdline Flattened Device Tree."
>>>
>>> Today, I spent time investigating these issues. It appears that U-Boot
>>> retrieves several variables from the Raspberry Pi firmware, with fdt_addr
>>> being particularly important.
>>> If the environment is saved, fdt_addr gets stored and takes precedence
>>> over what the firmware provides to U-Boot.
>>>
>>> Interestingly, the RPi firmware seems to modify fdt_addr based on connected
>>> hardware.  Our experiments showed that even attaching an RPi camera module
>>> changes the computed fdt_addr and U-Boot reads from the wrong memory location.
>>>
>>> As a result, saving the environment, whether via the saveenv command in U-Boot
>>> or fw_setenv in Linux, can lead to boot failures if the hardware configuration changes.
>>>
>>> Do you have any suggestions for mitigating this issue?
>>> In my opinion, U-Boot should not override such critical variables.
>>>
>>> Thanks,
>>> //richard
>>>
>>
>> Hi Richard,
>>
>> could be related tho this [1]?
>>
>> I sent this patch some years ago but was never accepted in u-boot tree.
>> But meta-rpi uses it in u-boot recipe [2].
> 
> After digging into this and a discussion with Tom we decided this is
> the correct fix so I've pulled that patch in for 2025.07.
> 
> Thanks,
> Peter
> 

Hi Peter,

thank you.

Regards

Mauro

>> Regards
>>
>> [1] https://lists.denx.de/pipermail/u-boot/2021-May/449609.html
>> [2]
>> https://github.com/agherzan/meta-raspberrypi/blob/master/recipes-bsp/u-boot/files/0001-rpi-always-set-fdt_addr-with-firmware-provided-FDT-address.patch
>>
>> --
>> Mauro
>