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by megous 237 days ago
It's not a dependency for Linux boot at all. You can do well with serial port alone, as anyone who brought up eg. an ARM SoC in Linux will attest to.

Also it's not very interesting either. At simplest, Linux just needs to take a pointer to a beginning of a framebuffer and some metadata, and will write to the framebuffer whenever there's something to update.
3 comments
okanat 237 days ago
If you would like to see an actually "interesting" boot, I recommend checking out how Raspberry Pi's boot.

It is a unique monstrosity that boots from the video / GPU core instead of one of the ARM cores. It has an arcane undocumented architecture.

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megous 236 days ago
When I realized that, after buying my first Rpi (2B), that was the last Rpi I ever bought. :)

Thankfully, pretty much everyone else just uses U-Boot.

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superkuh 237 days ago
Maybe not linux specifically, but POST requires a video device software (BIOS Option ROM or UEFI GOP Drivers) of some sort does it not? That's been my experience with all PCs for 30 years. But maybe there are cases where it doesn't?

edit: Apparently it's a desktop motherboard firmware thing. Ubiquitous but not technically a requirement for POSTing a computer.

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GreenVulpine 237 days ago
I've found AM4/AM5 boards will still boot Linux without a discrete or integrated GPU, running a GPUless CPU, not an APU.
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p_l 237 days ago
It was sorta required by IBM PC compatibles, but is not required by UEFI which supports serial console (or other interfaces).

IBM PC assumed existence of graphic output and sometimes Option ROMs did really too crazy things with it, I still have shivers when I hear "intel raid card" because of that one with possibly Win3.x in ROM...

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edoceo 237 days ago
Soekris (rip) had an x86 network device. Four 10/100s and the disk was a CF. Could only serial console that thing - or SSH once it's running. Best router I ever had.

Also, in 2000 when Windows crashed you could get a serial debugger. Wonder if they still do that?

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okanat 237 days ago
People still need to do driver ddvelopement. So you can still set up a Windows PC to expose kernel debug interface over serial port: https://learn.microsoft.com/en-us/windows-hardware/drivers/d...
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