[PATCH] rpi: always set fdt_addr with firmware-provided FDT address

[Ricardo Salveti]

On Wed, Sep 29, 2021 at 1:49 PM Matthias Brugger <mbrugger at suse.com> wrote:
> On 29/09/2021 14:19, Mauro Salvini wrote:
> > Hi Matthias,
> >
> > On 29/09/21 13:41, Matthias Brugger wrote:
> >> Hi Mauro,
> >>
> >> On 29/09/2021 12:14, Mauro Salvini wrote:
> >>> Hi Matthias
> >>>
> >>> On 15/09/21 13:16, mbrugger at suse.com (Matthias Brugger) wrote:
> >>>> Hi Mauro,
> >>>>
> >>>> On 07/06/2021 11:27, Mauro Salvini wrote:
> >>>>> On 12/05/21 14:39, Mauro Salvini wrote:
> >>>>>> Raspberry firmware prepares the FDT blob in memory at an address
> >>>>>> that depends on both the memory size and the blob size [1].
> >>>>>> After commit ade243a211d6 ("rpi: passthrough of the firmware provided FDT
> >>>>>> blob") this FDT is passed to kernel through fdt_addr environment variable,
> >>>>>> handled in set_fdt_addr() function in board file.
> >>>>>>
> >>>>>> When u-boot environment is persistently saved, if a change happens
> >>>>>> in loaded FDT (e.g. for a new overlay applied), firmware produces a FDT
> >>>>>> address different from the saved one, but u-boot still use the saved
> >>>>>> one because set_fdt_addr() function does not overwrite the fdt_addr
> >>>>>> variable. So, for example, if there is a script that uses fdt commands for
> >>>>>> e.g. manipulate the bootargs, boot hangs with error
> >>>>>>
> >>>>>> libfdt fdt_check_header(): FDT_ERR_BADMAGIC
> >>>>>>
> >>>>>> Removing the fdt_addr variable in saved environment allows to boot.
> >>>>>>
> >>>>>> With this patch set_fdt_addr() function always overwrite fdt_addr value.
> >>>>>>
> >>>>>> [1] https://www.raspberrypi.org/forums//viewtopic.php?f=107&t=134018
> >>>>>>
> >>>>
> >>>> First of all sorry for the very late reply.
> >>>> I'm hesitant to apply this patch, basically because it can break other setups
> >>>> where people load a custom DTB to fdt_addr.
> >>>>
> >>>> I wonder why you can't erase fdt_addr from your persistent storage. There is a
> >>>> command called eraseenv that should to the job.
> >>>
> >>> Sorry me too for the late reply.
> >>>
> >>> So your suggestion is to erase the fdt_addr variable from the environment
> >>> each time one needs to "refresh" it (one example could be the situation that
> >>> I ponted out).
> >>>
> >>> Yes, this could be the solution, but the need to delete the fdt_addr variable
> >>> when e.g. one changes the dtb loaded by rpi firmware should be documented
> >>> somewhere.
> >>>
> >>
> >> Hm, maybe I didn't understand the problem. My understanding is, that when you
> >> save the environment with saveenv, you also save the fdt_addr. And that's a
> >> problem because if you add a overlay later, the fdt_addr changed, which will
> >> not be reflected. So my question was if you couldn't just delete the fdt_addr
> >> variable from you saved environment so that when lateron you load overlays,
> >> you won't hit the problem. >
> >> My understanding was that you are setting a custom environment for your
> >> boards, but later your customers might add a overlay via e.g. config.txt and
> >> that will break booting the system.
> >>
> >> But from your response it seems thats not what you are experiencing. Or do you
> >> change the DTB loaded from FW in the U-Boot shell?
> >
> >
> > Maybe I wasn't too clear in my explanation ;-)
> >
> > At every boot, u-boot executes set_fdt_addr() function. At the very first boot,
> > if nobody has changed the default u-boot environment built in u-boot, adding a
> > custom fdt_addr variable, this function saves the fdt_addr variable in
>
> Which function are we talking about? Adding a custom fdt_addr can be done via
> the CLI or by adding that to the U-Boot sources (include/configs/rpi.h) but not
> through a 'function'.
>
> Do you mean that in some script you made saveenv is called? I used overlays in
> RPi and never had that problem.
>
> Actually I'm a bit puzzled about the problem. Can you give me a step by step
> reproducer, starting with which config I should use to compile U-Boot?

Yes, this issue only happens if you save the environment at least
once, as then on following boots it won't set the address based on
what the firmware uses, but instead restore the value from the saved
environment, which can be wrong.

I noticed the same when moving one sdcard between boards, and I was
only able to get it to boot correctly after removing the saved
environment.

Cheers,
-- 
Ricardo Salveti