176 lines
7.5 KiB
Markdown
176 lines
7.5 KiB
Markdown
---
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title: BSD operating systems
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x-toc-enable: true
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...
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Guide last updated on 16 November 2022.
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NOTE: This guide pertains to x86 hosts, and does not cover supported CrOS/ARM
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chromebooks. For ARM targets, you should refer to u-boot documentation.
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libreboot is capable of booting many BSD systems. This section mostly documents
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the peculiarities of libreboot as it pertains to BSD; you can otherwise refer to
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the official documentation for whatever BSD system you would like to use.
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Kernel Mode Setting
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===================
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Your BSD system *must* support Kernel Mode Setting for your graphics
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device (most of them do nowadays). The reasons will become apparent, as
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you read this article.
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Boot BSD, using SeaBIOS
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=======================
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On x86 platforms, Libreboot provides the choice of GRUB and/or
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SeaBIOS payload. GRUB can technically boot BSD kernels, but the code is
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poorly maintained and unreliable for this use-case scenario; on BIOS systems,
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GRUB can chainload BSD bootloaders, but on bare metal (as coreboot payload),
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GRUB can only chainload other coreboot payloads or boot Linux/BSD kernels
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directly (but direct booting is only really reliable for Linux, in GRUB).
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It is recommended that you boot in text mode, with SeaBIOS. You can literally
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just follow the official installation guides for your BSD system, whether it
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be FreeBSD, OpenBSD or others.
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If you don't plan to set up Xorg/Wayland, then that's all you really need to
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do. For example, you might want to run a headless server, in which case you
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probably don't mind running in text mode all the time.
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OpenBSD and corebootfb
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----------------------
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It's still recommended to use SeaBIOS in text mode, but OpenBSD specifically
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can work with SeaBIOS booting in a coreboot framebuffer, with SeaVGABIOS. In
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Libreboot ROM images, this would be SeaBIOS images with `corebootfb` in the
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file name.
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Make sure to select MBR-style partitioning on the installer, and it will
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Just Work.
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If you're using the GRUB payload but SeaBIOS is available in the boot menu,
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you can just select SeaBIOS at said menu, and OpenBSD will work fine.
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FreeBSD and corebootfb
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----------------------
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Assumed broken, so please ensure that you boot with SeaBIOS payload in text
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mode (lbmk ROM images with `txtmode` in the file name, not `corebootfb`).
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Warnings for X11 users
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----------------------
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One important peculiarity of most libreboot and libreboot systems is: VGA mode
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support exists, if booting with corebootfb (coreboot's own framebuffer) and
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the SeaVGABIOS option ROM used in the SeaBIOS payload; however, the ability
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to switch modes is not present, which means you can't switch to text mode
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either.
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Coreboot can start in framebuffer (corebootfb) or INT10H text mode, and it
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stays in whatever mode was set, unless KMS is used to change the mode. It
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should be noted that the coreboot framebuffer is not a VGA mode, but instead
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coreboot implements minimal drivers for hardware that it supports, providing
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a framebuffer directly in memory, which software (such as GRUB) can simply
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use.
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The BSD bootloaders on x86, in BIOS systems, typically expect text mode
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startup. It is usually possible to set the console to higher VGA modes,
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on most systems, but not on most coreboot systems with native video
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initialisation used, due to the quirks already described. If you see any
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documentation (in BSD land) pertaining to VESA modes, ignore it entirely;
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unless you're using the proprietary VGA ROM for your device, it won't work,
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and Libreboot doesn't distribute these (instead, coreboot's own video
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initialisation is used where possible, or a headless SeaBIOS payload setup
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is provided, where you would either run it headless or install a graphics
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card).
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Now, this would otherwise mean: no X11/Wayland. If you start in corebootfb
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mode with SeaVGABIOS, you won't get a display in BSD bootloaders, and if you
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boot in text mode, you can't set VESA modes from BSD. However, you're in luck:
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At least OpenBSD and FreeBSD (possibly others) all have excellent KMS
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support nowadays; short for `Kernel Mode Setting`. This avoids the inefficiency
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of BIOS/UEFI methods, by having the kernel set modes directly. It is based on
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KMS drivers that the BSD projects ported over from the Linux kernel. With this,
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you can use X11/Wayland in FreeBSD (and just X11 in OpenBSD, for now).
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For example: on FreeBSD, you can install `graphics/drm-kmod` as a package
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or from ports, and (for Intel GPUs) do this:
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sysrc kld_list+="i915kms"
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This creates the following entry in `/etc/rc.conf`:
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kld_list="i915kms"
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On FreeBSD it is also recommended that you switch to KMS on the console/TTY;
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add this to `/boot/loader.conf` so that you can still use the console after
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terminating Xorg:
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kern.vty=vt
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You should not rely on the above instruction (for FreeBSD), because the exact
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step might change, and it does not go into full detail either. Refer to the
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documentation provided by your system, to know how KMS is configured.
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ALWAYS READ THE MANUAL
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----------------------
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All of the BSDs have *excellent* documentation; it's one of the defining
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characteristics, versus typical Linux distros.
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Aside from this quirk in coreboot, regarding *BIOS* video modes, the BSDs
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otherwise work in exactly the same way as you would expect, and you can
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follow along to their official documentation without much fuss.
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No specific or detailed guides will be provided here, because SeaBIOS is
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fairly self-explanatory; you can otherwise refer to the SeaBIOS
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documentation.
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If you're flashing a ROM for a machine where `seabios_withgrub`
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and `seabios_grubfirst` ROMs are available, choose `seabios_withgrub`.
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DO NOT USE ROM IMAGES WITH `seabios_grubfirst` IN THE FILE NAME! These were
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present in older Libreboot releases, and supported in previous revisions
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of the build system, but they did not work for the intended purpose. More
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info is written on the [Libreboot installation guide](../install/). ROM
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images with `seabios_grubfirst` in the filename will NOT be included in
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future Libreboot releases.
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Dubious mention: Tianocore
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--------------------------
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Tianocore is extremely bloated, and unauditable, so it is not included
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in Libreboot firmware, but it is the reference UEFI implementation by
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Intel and contributors. It can boot most BSD systems very well.
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More robust ways to provide UEFI services in Libreboot are to be investigated.
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Tianocore integration will not be provided officially, in any current or future
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releases of Libreboot.
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Desktop users
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-------------
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NOTE: This section may not be full accurate; for example, the hardware page
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about HP Elite 8200 SFF talks about use of graphics cards on both corebootfb
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and txtmode setups, and seems to work fine with SeaBIOS in both cases.
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Desktop users on Libreboot should just install a graphics card,
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and again boot with SeaBIOS in text mode; however, when you do this,
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SeaBIOS will execute the VGA option ROM on the card which will provide
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early video initialisation instead of coreboot's initialisation, and that
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VGA ROM will usually implement full INT10H modes, including the ability
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to set modes in the BIOS (using interrupts), in which case you don't
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need to worry about Kernel Mode Setting, but you should still use KMS
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anyway.
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The reason to use KMS is because it's more efficient. The INT10H service can
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only be called in Real Mode or Virtual 8086 mode; v8086 is unavailable in
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long mode (x86\_64) and switching into Real Mode just to set VGA modes is
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extremely expensive computationally speaking. This is why modern kernels
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(Linux and BSD one) do mode setting themselves.
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You can learn more about INT10H text/VGA modes here:
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<https://en.wikipedia.org/wiki/INT_10H>
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