I have a Librem 13 v3 with PureBoot, and trying to boot the Debian 10 installer from a USB disk.
If I select the USB disk through the PureBoot menus, it detects the GRUB configuration and shows me the various installation options. And from what I can tell, it actually boots the kernel, but the display is unreadable.
Specifically, at the very top of the screen I see a band of colorful pixels, some of which change when I press the arrow keys. So it appears that PureBoot has configured the framebuffer in some particular mode, and the Debian installer kernel is trying to reuse the same framebuffer but expects it to be a different resolution or depth or something.
This happens both for the “text mode” and “graphical” Debian installers (which use the same kernel image but different initramfses.)
Any ideas? Has anybody else encountered this?
Is there any way to get PureBoot to launch GRUB from the USB disk (rather than trying to load Linux itself)? Is there a kernel command-line option that I could pass (using kexec from the PureBoot emergency shell) to tell Linux to use the same framebuffer mode that PureBoot uses, or else to reinitialize the framebuffer in some other compatible mode? (I don’t care if it’s 640x480, I just need it to be readable!)