Feature #476: Add option to convert coreboot-inited linear frame buffer to efifb directly - coreboot - Issue Tracker

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Feature #476

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Add option to convert coreboot-inited linear frame buffer to efifb directly

Added by Bill XIE over 1 year ago. Updated 6 months ago.

Status:

New

Priority:

Normal

Assignee:

Category:

coreboot common code

Target version:

none

Start date:

03/30/2023

Due date:

% Done:

70%

Estimated time:

Affected versions:

Needs backport to:

Affected hardware:

Affected OS:

GNU/Linux

Description

Currently, the linear frame buffer that coreboot initializes should be handled by Linux kernel with dedicated driver "simplefb", but most installer of GNU/Linux distributions only enables "efifb" support, which causes a GNU/Linux installer kexec-ed from a Linux payload running atop simplefb unable to output graphics.

Currently, Grub payload could turn coreboot-initialized simplefb to efifb, which can be easily examined from the dmesg log of GNU/Linux booted from Grub payload running atop coreboot-inited linear frame buffer (simplefb). Chainloading a Linux payload with a minimal Grub payload only containing module "linux" and "cbfs" could make the Linux payload running atop efifb, of which GNU/Linux installers can make use, but the related code could be ported to coreboot to make things easier.

Related links

https://review.coreboot.org/c/coreboot/+/76428
https://review.coreboot.org/c/coreboot/+/76431
https://review.coreboot.org/c/coreboot/+/76479

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Updated by Bill XIE over 1 year ago

"Grub payload could turn coreboot-initialized simplefb to efifb" turns out that grub payload can read video mode info from the coreboot table and fill them into a struct linux_kernel_params in include/grub/i386/linux.h (corresponding to struct linux_params of util/cbfstool/linux.h and struct screen_info in include/uapi/linux/screen_info.h of Linux kernel) to boot the Linux kernel, and set the member have_vga (corresponding to orig_video_isVGA of struct linux_params and struct screen_info) to GRUB_VIDEO_LINUX_TYPE_SIMPLE (0x70, corresponding to VIDEO_TYPE_EFI in Linux kernel), allowing the driver efifb to take over the framebuffer.