Unexpected RPi5 Behavior with Saved U-Boot Environment

[Peter Robinson]

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

> 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