docs: add doc for using rpi4 as server.

This guide explains how to use RPI4 as servers when using sidero.

Closes: siderolabs/talos#3621

Signed-off-by: Kevin Hellemun <17928966+OGKevin@users.noreply.github.com>

website/content/docs/v0.3/Guides/rpi4-as-servers.md

@@ -0,0 +1,186 @@
+---
+description: "Using Raspberrypi pi 4 as servers"
+weight: 6
+---
+
+# Raspberrypi4 as servers
+
+This guide will explain on how to use Sidero to manage Raspberrypi-4's as
+servers. This guide goes  hand in hand with the [bootstrapping
+guide](/docs/v0.3/guides/bootstrapping).
+
+From the bootstrapping guide, reach "Install Sidero" and come back to this
+guide. Once you finish with this guide, you will need to go back to the
+bootstrapping guide and continue with "Register the servers".
+
+The rest of this guide goes with the assumption that you've a cluster setup with
+sidero and ready to accept servers. This guide will explain the changes that
+needs to be made to be able to accept RPI4 as server.
+
+# RPI4 boot process
+To be able to boot talos on the Pi4 via network, we need to undergo a 2 step
+boot process. The Pi4 has an EEPROM which contains code to boot up the Pi. This
+EEPROM expects a specific boot folder structure as explained on
+[this](https://www.raspberrypi.org/documentation/configuration/boot_folder.md) page.
+We will use the EEPROM to boot into UEFI, which we will then use to PXE and iPXE boot into sidero & talos.
+
+# Prerequisites
+## Update EEPROM
+To enable the EEPROM on the Pi to support network booting, we must update it to
+the latest version. Visit the
+[release](https://github.com/raspberrypi/rpi-eeprom/releases) page and grab the
+latest `rpi-boot-eeprom-recovery-*-network.zip` (as of time of writing,
+v2021.0v.29-138a1 was used). Put this on a SD card and plug it into the Pi. The
+Pi's status light will flash rapidly after a few seconds, this indicates that
+the EEPROM has been updated.
+
+This operation needs to be done once per Pi.
+
+## Serial number
+Power on the Pi without an SD card in it and hook it up to a monitor,
+
+<!-- todo: Explain how to get serial number from this page -->
+
+## talos-systems/pkg
+Clone the [talos-systems/pkg](https://github.com/talos-systems/pkgs) repo.
+Create a new folder called `raspberrypi4-eufi` and `raspberrypi4-eufi/serials`.
+Create a file `raspberrypi4-eufi/pkg.yaml` containing the following:
+```
+name: raspberrypi4-eufi
+variant: alpine
+install:
+  - unzip
+steps:
+# {{ if eq .ARCH "aarch64" }} This in fact is YAML comment, but Go templating instruction is evaluated by bldr restricting build to arm64 only
+  - sources:
+      - url: https://github.com/pftf/RPi4/releases/download/v1.26/RPi4_UEFI_Firmware_v1.26.zip # <-- update version NR accordingly.
+        destination: RPi4_UEFI_Firmware.zip
+        sha256: d6db87484dd98dfbeb64eef203944623130cec8cb71e553eab21f8917e0285f7
+        sha512: 96a71086cdd062b51ef94726ebcbf15482b70c56262555a915499bafc04aff959d122410af37214760eda8534b58232a64f6a8a0a8bb99aba6de0f94c739fe98
+    prepare:
+      - |
+        unzip RPi4_UEFI_Firmware.zip
+        rm RPi4_UEFI_Firmware.zip
+        mkdir /rpi4
+        mv ./* /rpi4
+    install:
+      - |
+        mkdir /rootfs
+        ls /pkg/serials | while read serial; do mkdir /rootfs/$serial && cp -r /rpi4/* /rootfs/$serial && cp -r /pkg/serials/$serial/* /rootfs/$serial/; done
+# {{ else }}
+  - install:
+      - |
+        mkdir -p /rootfs
+# {{ end }}
+finalize:
+  - from: /rootfs
+    to: /
+```
+
+# EUFI / RPi4
+
+Now that the EEPROM can network boot, we need to prepare the structure of our
+boot folder. Essentially what the bootloader will do is look for the this folder
+on the network rather than on the SD card.
+
+Visit the [release page of RPi4](https://github.com/pftf/RPi4/releases) and grab
+the latest `RPi4_UEFI_Firmware_v*.zip` (at the time of writing, v1.26 was used).
+Extract the zip into a folder, the structure will look like the following:
+
+```
+.
+├── RPI_EFI.fd
+├── RPi4_UEFI_Firmware_v1.26.zip
+├── Readme.md
+├── bcm2711-rpi-4-b.dtb
+├── bcm2711-rpi-400.dtb
+├── bcm2711-rpi-cm4.dtb
+├── config.txt
+├── firmware
+│   ├── LICENCE.txt
+│   ├── Readme.txt
+│   ├── brcmfmac43455-sdio.bin
+│   ├── brcmfmac43455-sdio.clm_blob
+│   └── brcmfmac43455-sdio.txt
+├── fixup4.dat
+├── overlays
+│   └── miniuart-bt.dtbo
+└── start4.elf
+```
+As a one time operation, we need to configure EUFI to do network booting by
+default, remove the 3gb mem limit if it's set and optionally set the CPU clock to
+max.
+Take these files and put them on the SD card and boot the Pi. You will see
+the Pi logo and the option to hit `esc`.
+
+<!-- todo: explain how to change boot order, mem, and cpu -->
+
+When you hit `reset`, the settings will be save to the `RPI_EFI.fd` file on the
+SD card. This is where we will run into a limitation that is explained in the
+following issue: https://github.com/pftf/RPi4/issues/59. What this mean is that
+we need to create a `RPI_EFI.fd` file for each Pi that we want to use as server.
+This is because that the MAC address is also stored in the `RPI_EFI.fd` file,
+which makes it invalid when you try to use it in a different Pi.
+
+Plug the SD card back into your computer and extract the `RPI_EFI.fd` file from
+it and place it into the `raspberrypi4-eufi/serials/<serial>/`. The dir should
+look like this:
+```
+raspberrypi4-eufi/
+├── pkg.yaml
+└── serials
+    └─── XXXXXXXX
+        └── RPI_EFI.fd
+```
+
+# Build the image with the boot folder contents
+Now that we have the `RPI_EFI.fd` of our Pi in the correct location, we must now
+build a docker image containing the boot folder for the EEPROM. To do this, run
+the following command in the pkgs repo:
+
+`make PLATFORM=linux/arm64 USERNAME=$USERNAME PUSH=true TARGETS=raspberrypi4-eufi`
+
+This will build and push the following image:
+`ghcr.io/ogkevin/raspberrypi4-eufi:<tag>`
+
+_If you need to change some other settings like registry etc, have a look in the
+Makefile to see the available variables that you can override._
+
+The content of the image will be the following:
+
+```
+280b960e
+├── RPI_EFI.fd
+├── Readme.md
+├── bcm2711-rpi-4-b.dtb
+├── bcm2711-rpi-400.dtb
+├── bcm2711-rpi-cm4.dtb
+├── config.txt
+├── firmware
+│   ├── LICENCE.txt
+│   ├── Readme.txt
+│   ├── brcmfmac43455-sdio.bin
+│   ├── brcmfmac43455-sdio.clm_blob
+│   └── brcmfmac43455-sdio.txt
+├── fixup4.dat
+├── overlays
+│   └── miniuart-bt.dtbo
+└── start4.elf
+```
+
+# Patch metal controller
+To enable the 2 boot process, we need to include this EEPROM boot folder into
+the sidero's tftp folder. To achieve this, we will use a init container using
+the image we created above to copy the contents of it into the tftp folder.
+
+<!-- todo: explain how to create init container  with shared empty dir between
+sidero and init container -->
+
+<!-- cp / /var/lib/sidero/tftp should be it-->
+
+# Profit
+
+With the patched metal controller, you should not be able to register the Pi4 to
+sidero by just connecting it to the network. From this point you can continue
+with the [bootstrapping
+guide](/docs/v0.3/guides/bootstrapping) at "Register the servers".