I see the sibling comment, so here's my two cents -
I wonder if there's some confusion because LinuxBoot is being talked about relative to Oxide. LinuxBoot isn't trying to do that.
It was originally a project called "LinuxBIOS" at Los Alamos National Labs to get their supercomputer to boot up in a reasonable amount of time. Once the team started down the path of "rip out the legacy BIOS" they discovered that a lot of things become simpler.
LinuxBoot was written with the goal of booting up the machine to GRUB, like this:
(CPU Reset) > LinuxBIOS > GRUB > Linux
See the description of this video (though the video is worth the watch): https://vimeo.com/724454408 "Why Linux? Because firmware always evolves to become an operating system. Rather than wait for evolution to take its course, LANL decided to save some time and use Linux as the BIOS: hence LinuxBIOS."
And the answer to your question: "could you start booting up userland directly?" I think if the LinuxBoot authors were around they would mention something about how constrained the on-board flash chip is (SPI Flash). There's room for LinuxBoot and maybe GRUB, but there is not room for all the drivers needed to get to userland.
I wonder if there's some confusion because LinuxBoot is being talked about relative to Oxide. LinuxBoot isn't trying to do that.
It was originally a project called "LinuxBIOS" at Los Alamos National Labs to get their supercomputer to boot up in a reasonable amount of time. Once the team started down the path of "rip out the legacy BIOS" they discovered that a lot of things become simpler.
LinuxBoot was written with the goal of booting up the machine to GRUB, like this:
(CPU Reset) > LinuxBIOS > GRUB > Linux
See the description of this video (though the video is worth the watch): https://vimeo.com/724454408 "Why Linux? Because firmware always evolves to become an operating system. Rather than wait for evolution to take its course, LANL decided to save some time and use Linux as the BIOS: hence LinuxBIOS."
See also https://lwn.net/Articles/10590/
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And the answer to your question: "could you start booting up userland directly?" I think if the LinuxBoot authors were around they would mention something about how constrained the on-board flash chip is (SPI Flash). There's room for LinuxBoot and maybe GRUB, but there is not room for all the drivers needed to get to userland.