NixOS on ARM/Raspberry Pi 5: Difference between revisions
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=== Generic UEFI boot support === | === Generic UEFI boot support === | ||
NixOS doesn't run out-of-box, but relies on several tweaks on the boot process that are maintained by different individuals and spread over multiple repositories. The Raspberry Pi 5's boot process follows the [https://youtu.be/UvFG76qM6co?t=308 typical boot stages on embedded devices], and has the following boot loader steps by default: | NixOS doesn't run out-of-box, but relies on several tweaks on the boot process that are maintained by different individuals and spread over multiple repositories. The Raspberry Pi 5's boot process follows the [https://youtu.be/UvFG76qM6co?t=308 typical boot stages on embedded devices], and has the following boot loader steps by default:{{caption|align=center|{{mermaid|flowchart LR| | ||
[[ | ROM --> EEPROM | ||
EEPROM --> FK[Firmware / Kernel] | |||
FK --> OS[Raspberry Pi OS] | |||
}}|The normal boot process of a Raspberry Pi 5|alt=A flowchart showing 4 boxes with text in each, one leading to another. In the first box, ROM. In the second, EEPROM. In the third, Firmware / Kernel. In the fourth, Raspberry Pi OS.}} | |||
The pain points for NixOS support are the Pi's [https://github.com/raspberrypi/rpi-eeprom custom EEPROM boot bootloader], its [https://github.com/raspberrypi/firmware proprietary, closed-source firmware] (code to use to hardware components) and [https://github.com/raspberrypi/linux its separately maintained Linux kernel], all of which we would need to update, build and test constantly and separately from the other NixOS Linux kernel variations, which is a large, unmaintainable burden for the NixOS community when the Pi 5 is not the only supported SoC. | The pain points for NixOS support are the Pi's [https://github.com/raspberrypi/rpi-eeprom custom EEPROM boot bootloader], its [https://github.com/raspberrypi/firmware proprietary, closed-source firmware] (code to use to hardware components) and [https://github.com/raspberrypi/linux its separately maintained Linux kernel], all of which we would need to update, build and test constantly and separately from the other NixOS Linux kernel variations, which is a large, unmaintainable burden for the NixOS community when the Pi 5 is not the only supported SoC. | ||
The more sustainable goal would be to move towards UEFI support, which would mimic how desktop computers boot into the NixOS operating system, thus minimising the amount of bespoke maintenance needed for the development board. This is what this process would look like: | The more sustainable goal would be to move towards UEFI support, which would mimic how desktop computers boot into the NixOS operating system, thus minimising the amount of bespoke maintenance needed for the development board. This is what this process would look like: | ||
[[ | {{caption|align=center|{{mermaid|flowchart LR| | ||
ROM --> EEPROM | |||
EEPROM --> UEFI[UEFI Bootloader] | |||
UEFI --> SD[Systemd Bootloader] | |||
SD --> LK[Generic Linux Kernel] | |||
LK --> OS[Raspberry Pi OS] | |||
}}|The ideal Raspberry Pi 5 boot process|alt=A flowchart containing 5 boxes with text. In this order, each box contains the following: ROM, EEPROM, UEFI Bootloader, Systemd Bootloader, Generic Linux Kernel, and NixOS.}} | |||
The ROM and EEPROM can't be modified, as they are built into the hardware on the development board. However, [https://de.wikipedia.org/wiki/Unified_Extensible_Firmware_Interface UEFI] is also used for booting normal Intel/AMD computers, and the [https://www.freedesktop.org/software/systemd/man/latest/systemd-boot.html systemd-boot] boot loader is THE software that allows us to have and select from multiple NixOS generations on boot (and perform rollbacks if we messed up). Further details about the steps involved in achieving this can be found in the ''Other Solutions'' section, under ''Generic UEFI Boot.'' | The ROM and EEPROM can't be modified, as they are built into the hardware on the development board. However, [https://de.wikipedia.org/wiki/Unified_Extensible_Firmware_Interface UEFI] is also used for booting normal Intel/AMD computers, and the [https://www.freedesktop.org/software/systemd/man/latest/systemd-boot.html systemd-boot] boot loader is THE software that allows us to have and select from multiple NixOS generations on boot (and perform rollbacks if we messed up). Further details about the steps involved in achieving this can be found in the ''Other Solutions'' section, under ''Generic UEFI Boot.'' | ||
Finally, there should also be [https://github.com/u-boot/u-boot U-Boot] support soon, as most development boards are widely supported by the project. In that case, the boot process would look like: | Finally, there should also be [https://github.com/u-boot/u-boot U-Boot] support soon, as most development boards are widely supported by the project. In that case, the boot process would look like: | ||
[[ | {{caption|align=center|{{mermaid|flowchart LR| | ||
ROM --> EEPROM | |||
EEPROM --> FK[Firmware / Kernel] | |||
FK --> U[U-Boot Bootloader] | |||
U --> OS[Raspberry Pi OS] | |||
}}|Theoretical Raspberry Pi 5 U-Boot boot process|alt=A flowchart showing 5 boxes containing text. In this order, each box contains the following text: ROM, EEPROM, Firmware or Kernel, U-Boot, and NixOS.}} | |||
== Proposed Solution == | == Proposed Solution == | ||