[bug#44543] [PATCH] gnu: raspberry-pi: Add helpers for config.txt file generation.

[Stefan]

Hi Léo!

> I have a Raspberry Pi 3B+ here at home, how can I test these changes?
> 
> I don't feel capable to review this without testing something as a
> whole verifying that it works then inspecting these things that make it
> work.

The support for the Raspberry is still not complete. I’m using mine without an 
SD card, booting it over TFTP with an NFS root mount.

Installing on an SD card is not tested and certainly not working yet.

One of my next patches will be several u-boot packages for different Raspberry 
models. To build them I need to do changes to the defconfig file of u-boot. 
Therefore another ticket is pending, which eases defconfig modifications 
(<http://issues.guix.gnu.org/45046>, and I hope this can also be used to modify 
Linux). When that one is done, then I will send that next patch to add the 
u-boot packages. 

My bootloader currently looks like this, but I’m using already further 
modifications, mainly for GRUB, so this will not work for you, but you can get 
an impression of the final intended use of all patches:

  (bootloader
    (bootloader-configuration
      (target "/boot")
      (bootloader (efi-bootloader-chain
                   grub-efi-netboot-removable-bootloader
                   ;; Packages needed to boot the Raspberry.
                   #:packages (list raspberrypi-firmware 
                                    u-boot-rpi-efi-64)
                   ;; Additional files for configuration.
                   #:files (list ;; Detects 32 or 64 bit, includes other txt 
files.
                                 raspi-config-txt
                                 ;; Use the downstream device tree (upstream is 
bcm28).
                                 raspi-bcm27-dtb-txt
                                 ;; This is the next boot stage.
                                 raspi-u-boot-bootloader-txt 
                                 ;; Additional configurations to use.
                                 (raspi-custom-txt '("disable_overscan=1"
                                                     "hdmi_force_hotplug=1"
                                                     "audio=on"
                                                     "dtoverlay=gpio-ir"
                                                     "dtoverlay=disable-wifi"
                                                     
"dtoverlay=vc4-fkms-v3d,cma-64")))))))

Your bootloader configuration would need to look like this, and you may get it 
running from an SD card:

  (bootloader
    (bootloader-configuration
      (target "/boot")
      (bootloader
        (efi-bootloader-chain
          (list (file-append firmware "/boot/")
                (file-append u-boot-my-scb "/libexec/u-boot.bin")
                raspi-config-txt
                raspi-bcm27-dtb-txt
                raspi-u-boot-bootloader-txt)
          grub-efi-netboot-bootloader
          #:installer
           (chain-efi-bootloader-installer (install-grub-efi-netboot 
"efi/boot")))))

So you need to provide firmware and u-boot (still) yourself. As a short cut you 
may omit both (file-append …) functions and copy both parts by hand from some 
other distribution, maybe openSUSE – this is basically how I got started.

If you mount an ext4-partition of an SD card to e.g. /my-target/ and the FAT 
partition to /my-target/boot, then you may try a ‘guix system init … 
/my-target’.

If this succeeds, then it may be possible that adding the file 
/my-target/boot/efi/boot/grub.cfg with this content gets you to a system 
booting from an SD card:

search --file /boot/grub/grub.cfg
configfile /boot/grub/grub.cfg

But this is all untested, it certainly fails. :-)

At least – regarding this patch – I can ensure that the three config files as 
used in these bootloader examples are properly generated working.
 

Bye

Stefan