Boot the kernel directly off the optical disk drive

[frno7]

Explain on the wiki how to install Linux on a DVD, similar to #4 (comment) but with a 5.x kernel. A guide has now been written for creating a bootable DVD for PlayStation 2 Linux. Plan:

• Linux 2.x with Black Rhino on models SCPH-7xxxx and SCPH-900xx;
• Linux 5.x with Gentoo Linux for the PlayStation 2;
• ...

[faissaloo]

I've created a basic tutorial that should work: https://github.com/frno7/linux/wiki/Creating-a-bootable-PS2-Slim-DVD

[frno7]

@faissaloo, perhaps we should make a note about what version of the Linux kernel the basic tutorial currently covers?

[faissaloo]

The tutorial should be version agnostic

[frno7]

Sure, but BOOT/VMLINUZ.GZ from the ISO must have some version? Something like this:

5. Replace ./BOOT/VMLINUZ.GZ (Linux kernel version 2.x.y) with your version of vmlinuz.gz

Also, the Black Rhino distribution won’t run properly with 4.x and 5.x kernels, because it uses R5900 128-bit multimedia instructions (LQ, SQ, PEXTLB, PEXTLW and so on in for instance /lib/ld.so). MMIs aren’t currently supported, see issue #5. Linux 2.x kernels are not IEEE 754 compatible, unlike 5.x kernels, as explained in issue #3. So versions are quite important until we have sorted out the issues, at the very least.

The initial patch submission, as discussed with kernel maintainers regarding issue #1, will be limited to the o32 psABI. In this regard, the Black Rhino build is nonstandard.

[faissaloo]

Oh sure, this tutorial isn't supposed to produce a Black Rhino iso, I've written it such that you replace/delete all the BlackRhino specific files. I've added some more detail now, let me know what you think. As long as this kernel can be booted with KernelLoader there should be no issues.

[frno7]

Thanks! I added a section Notes about R5900 Linux distributions and kernel versions to the guide. Last time I tried the Kernel Loader program it crashed when attempting to boot Linux 4.x and 5.x, so I assume that this will be a problem as well? In that case the kernel ought to be launched from wLaunchELF directly (as is usually done when launching 5.x kernels from a USB drive).

Eventually the kernel ought to be able to bypass even wLaunchELF and boot directly regardless of hardware state, but as noted in #4 we have a couple of initialisation issues to sort out first, starting with #9.

[faissaloo]

When it comes to launching directly, how do you handle passing kernel parameters? That's the main thing KernelLoader is for. I've added some information about what to do if you the disk to start a different ELF.

[frno7]

One more thing, I strongly suggest that the step 2 ought to be something like this:

2. Verify that the downloaded 7z archive file has SHA256 xxx.

The URL itself doesn’t look particularly trustworthy, and one should always verify downloads anyway!

[frno7]

When it comes to launching directly, how do you handle passing kernel parameters? That's the main thing KernelLoader is for.

Oh, that’s rather easy. Simply enable CMDLINE_BOOL and set CMDLINE to whatever parameters you need in your kernel config:

linux/arch/mips/Kconfig.debug

Lines 33 to 67 in 59a11ab

	config CMDLINE_BOOL
	bool "Built-in kernel command line"
	default n
	help
	For most systems, it is firmware or second stage bootloader that
	by default specifies the kernel command line options. However,
	it might be necessary or advantageous to either override the
	default kernel command line or add a few extra options to it.
	For such cases, this option allows you to hardcode your own
	command line options directly into the kernel. For that, you
	should choose 'Y' here, and fill in the extra boot arguments
	in CONFIG_CMDLINE.
	The built-in options will be concatenated to the default command
	line if CMDLINE_OVERRIDE is set to 'N'. Otherwise, the default
	command line will be ignored and replaced by the built-in string.
	Most MIPS systems will normally expect 'N' here and rely upon
	the command line from the firmware or the second-stage bootloader.
	config CMDLINE
	string "Default kernel command string"
	depends on CMDLINE_BOOL
	default ""
	help
	On some platforms, there is currently no way for the boot loader to
	pass arguments to the kernel. For these platforms, and for the cases
	when you want to add some extra options to the command line or ignore
	the default command line, you can supply some command-line options at
	build time by entering them here. In other cases you can specify
	kernel args so that you don't have to set them up in board prom
	initialization routines.
	For more information, see the CMDLINE_BOOL and CMDLINE_OVERRIDE
	options.

[frno7]

Additionally, as per #33 (comment), one can pass parameters to kernel modules in the initialisation scripts, like this:

modprobe ps2fb mode_option=1920x1080p@50 mode_margin=+13+0

The line above would load the Graphics Synthesizer frame buffer device driver and set the default video resolution to progressive 1920×1080 at 50 Hz, and then do some minor pixel adjustments as explained in:

linux/drivers/video/fbdev/ps2fb.c

Lines 2352 to 2358 in 00a55c7

	/*
	* Analogue devices are frequently a few pixels off. Use this mode_margin
	* option to make necessary device dependent adjustments to the built-in modes.
	*/
	module_param(mode_margin, charp, 0);
	MODULE_PARM_DESC(mode_margin,
	"Adjust initial video mode margin as \"<-|+><dx><-|+><dy>\"");

Video modelines are very flexible with 5.x kernels, unlike 2.x kernels that don’t handle 1920×1080.

[frno7]

Some more: I think the guide should be renamed by omitting the word slim so that we have a general DVD guide (incidentally, slim has unfortunate connotations that would best to avoid).

Then a step 0 ought to be to review the PlayStation 2 Linux hardware model compatibility, and make sure that one has SCPH-7xxxx or possibly SCPH-900xx. I know that 2.x kernels are fiddly getting to work with various models. 5.x kernels should be much better at this, in the sense that they shouldn’t be possible to misconfigure for any particular model (that is, if it boots on one, it should boot on all).

I put the USB alternative in the header. Eventually we should to link to a USB guide there (and vice versa, have the USB guide link to the DVD dito).

[frno7]

Ah, regarding spelling: all other wiki pages spell out PlayStation 2 in the titles, with no abbreviation like PS2. The DVD guide ought to follow suit.

[faissaloo]

I didn't even realise you could hardcode the kernel config. Thanks to your suggestion regarding verifying downloads I realised the download link I was using previous had truncated the file lol, so I've switched it to another site and added the SHA. I've also linked to the hardware compatibility for this kernel and fixed the abbreviations.