docs/arm: add info on Raspberry Pi 4

Change-Id: Ic8cc47394c9e49f05e30b5ba54ff70557b1e2c47
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5237
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

docs/develop/kernel/arch/arm/overview.rst

@@ -37,6 +37,7 @@ We have accumulated some notes and documentation on some of them.
    /kernel/arch/arm/rpi1
    /kernel/arch/arm/rpi2
    /kernel/arch/arm/rpi3
+   /kernel/arch/arm/rpi4
 
 TODO list
 ---------

docs/develop/kernel/arch/arm/rpi4.rst

@@ -0,0 +1,95 @@
+Raspberry Pi 4
+##############
+
+-  http://raspberrypi.org
+
+Hardware Information
+====================
+
+-  ARMv8 Architecture (64-bit)
+-  Broadcom BCM2711 (SoC)
+
+   -  Includes Quad ARM Cortex-A72 CPU @ 1.8 GHz
+   -  Includes VideoCore VI GPU
+
+-  SD Card Storage
+-  1, 2, 4 or 8 GB RAM
+-  Video Outputs
+
+   -  2x HDMI Video Output via micro-HDMI
+   -  Composite Video Output
+
+-  Ethernet 10/100/1000 Mbit/s
+-  Wifi b/g/n/ac dual band 2.4/5 GHz
+-  Bluetooth 5.0
+-  2x USB 2.0, 2x USB 3.0
+
+Setting up the Haiku SD card
+============================
+
+The Raspberry Pi SD card generally uses the MBR file system layout
+below. Partition 1 is all that is required to boot an OS.
+
+-  partition 1 – FAT32, bootable flag, type ‘ef’
+-  partition 2 – BeFS, Haiku filesystem, type ‘eb’
+
+Boot Partition
+--------------
+
+Required Files
+~~~~~~~~~~~~~~
+
+-  start4.elf: The GPU binary firmware image
+-  fixup4.dat: Additional code for the GPU
+-  bcm2711-rpi-4-b.dtb: FDT binary for the Raspberry Pi 4B
+-  bcm2711-rpi-400.dtb: FDT binary for the Raspberry Pi 400
+-  config.txt: A configuration file read by the Pi to start u-boot.bin
+-  u-boot.bin: u-boot loader for the Pi 4
+-  boot.scr: u-boot loader script for starting Haiku Loader
+-  uEnv.txt: configuration file for the boot.scr script
+-  haiku_loader.efi: Haiku Loader
+
+Note: unlike previous Raspberry Pi models, there's no bootcode.bin on the
+Raspberry Pi 4 as it's replaced by a boot EEPROM.
+
+Optional Files
+~~~~~~~~~~~~~~
+
+-  vlls directory: Additional GPU code, e.g. extra codecs.
+-  uEnv.txt: u-boot configuration script to automate boot.
+
+Compiling Haiku and preparing SD card
+=====================================
+
+-  Create your ARM work directory
+   ``mkdir generated.arm; cd generated.arm``
+-  Build an ARM toolchain using
+   ``../configure --build-cross-tools arm --cross-tools-source ../../buildtools``
+-  Build SD card image using ``jam -q -j6 @minimum-mmc``
+-  Prepare customized SD card using the ``rune`` tool. E.g. ``rune -b rpi4 -i haiku-mmc.image /dev/mmcblk0``
+
+Booting
+=======
+
+1. SOC starts the boot EEPROM
+2. Boot EEPROM runs start4.elf
+3. start4.elf reads config.txt and start u-boot
+4. u-boot.bin starts the Haiku loader
+5. Haiku loader boots Haiku kernel
+
+config.txt Options
+------------------
+
+::
+
+   uart_2ndstage=1
+   enable_uart=1
+   kernel=u-boot.bin
+
+
+Additional Information
+======================
+
+-  `Latest Raspberry Pi
+   firmware <http://github.com/raspberrypi/firmware/tree/master/boot>`__
+-  `config.txt options <http://www.elinux.org/RPiconfig>`__