Installing a PlayStation 2 Linux initramfs root filesystem

The initramfs is an initial root filesystem to be compiled into the PlayStation 2 Linux kernel.

There are two alternative guides to installing an initramfs root filesystem:

• downloading a precompiled initramfs archive from the actions menu, for either PAL or NTSC systems, or
• installing an initramfs with Gentoo.

Next, proceed by building a PlayStation 2 Linux kernel.

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Make sure that you have

• an R5900 Busybox, or proceed by installing an R5900 Busybox;
• the input/output processor (IOP) modules as IRX files to be installed as firmware in the root filesystem, or proceed by installing PlayStation 2 IOP modules.

Contents

• Install Busybox
• Create root filesystem
• Install /init
• Install /sbin/init
• Install IOP modules
• Install kernel modules

Install Busybox

In case you were building the busybox following the building an R5900 Busybox from sources guide, move the folder _install to the folder level near the kernel source folder; next, rename the folder _install into initramfs/ps2;

In case you were building the busybox following the building an R5900 Busybox using Gentoo Linux guide, copy the R5900 Busybox executable file into bin/. If Busybox is dynamically linked, copy related libraries into lib/.

Create root filesystem

In case you were building the busybox following the building an R5900 Busybox using Gentoo Linux guide, create the folder structure initramfs/ps2 so that it is reachable from the Linux kernel source directory using ../initramfs/ps2. This is the root directory of the initial root filesystem. Now do cd initramfs/ps2 and then

mkdir bin dev etc lib mnt proc root sbin sys tmp usr usr/bin usr/sbin var

In case you were building the busybox following the building an R5900 Busybox from sources guide, you already have the properly named initramfs/ps2 . But you should check for the absent folders noted in Gentoo Linux'es busybox case above. So just create the absent one's folders.

Pay attention to the file and directory ownerships, the UID and GID. In the kernel configuation file .config, set

CONFIG_INITRAMFS_ROOT_UID=1000
CONFIG_INITRAMFS_ROOT_GID=1000

if UID and GID are 1000, for instance. Review the Linux kernel documentation for CONFIG_INITRAMFS_ROOT_UID and CONFIG_INITRAMFS_ROOT_GID for details.

Install /init

Create an init text file with

#!/bin/busybox sh

/bin/busybox --install -s

/bin/mount -t devtmpfs devtmpfs /dev

exec 0</dev/console
exec 1>/dev/console
exec 2>/dev/console

exec /sbin/init $*

Then do chmod a+x init.

Install /sbin/init

Create an sbin/init text file with

#!/bin/sh

PATH=/usr/sbin:/usr/bin:/sbin:/bin
export PATH

mount -t sysfs none /sys
mount -t tmpfs none /var
mount -t tmpfs none /tmp
mount -t proc none /proc
mkdir /dev/pts
mount -t devpts none /dev/pts
mount -t debugfs none /sys/kernel/debug

depmod

modprobe ps2fb mode_option=1920x1080p@60

modprobe sif
modprobe iop-memory
modprobe iop-module
modprobe iop-irq

modprobe sd_mod
modprobe ohci-ps2
modprobe ums-usbat
modprobe usbhid
modprobe hid-generic

uname -a

sh

while :
do
	sleep 1
done

Then do chmod a+x sbin/init. The mode_option parameter to ps2fb can be adjusted, or removed, as necessary. The depmod command is most likely required to make kernel module dependencies compatible with the Busybox variant of modprobe, as it seems incompatible with the counterparts in kmod that is used with make modules_install. Most modprobe commands can be omitted, if kernel module dependencies are working properly.

Install IOP modules

Go into initramfs/ps2 folder. Assume that all 3 folders are on the same level: initramfs, iopmod, linux . Do mkdir -p lib/firmware/ps2 and copy the IRX files to this directory, for example using

cp ../../iopmod/module/*.irx lib/firmware/ps2/

Install kernel modules

As the initramfs is to be compiled into our kernel AND initramfs requires the kernel modules installed, first, we must build the kernel before we finalize the initramfs that we'll embed - so proceed with Building a PlayStation 2 Linux kernel. Once the kernel is built initially, return here and install the kernel modules using

make ARCH=mips CROSS_COMPILE=mipsr5900el-unknown-linux-gnu- INSTALL_MOD_PATH=../initramfs/ps2 INSTALL_MOD_STRIP=1 modules_install

To enlight the resulting kernel which includes the initramfs, you may remove the unneeded for the launch modules from the initramfs/lib/modules/ directory

The INITRAMFS is to be installed when building a PlayStation 2 Linux kernel.