I've been analysing the kernel's start-up code that sets the console.
The selection of the dummy console occurs in
drivers/video/console/vgacon.c::vgacon_startup()
There is a code label "novga" which results in the VGA console driver
not being used:
if (screen_info.orig_video_isVGA == VIDEO_TYPE_VLFB ||
screen_info.orig_video_isVGA == VIDEO_TYPE_EFI) {
no_vga:
#ifdef CONFIG_DUMMY_CONSOLE
conswitchp = &dummy_con;
return conswitchp->con_startup();
#else
return NULL;
#endif
The "novga" label is also reached from later code that checks
boot_params.screen_info has been initialized, and then whether the
screen is in a VGA16 mode not handled by VGACON.
/* boot_params.screen_info initialized? */
if ((screen_info.orig_video_mode == 0) &&
(screen_info.orig_video_lines == 0) &&
(screen_info.orig_video_cols == 0))
goto no_vga;
/* VGA16 modes are not handled by VGACON */
if ((screen_info.orig_video_mode == 0x0D) || /* 320x200/4 */
(screen_info.orig_video_mode == 0x0E) || /* 640x200/4 */
(screen_info.orig_video_mode == 0x10) || /* 640x350/4 */
(screen_info.orig_video_mode == 0x12) || /* 640x480/4 */
(screen_info.orig_video_mode == 0x6A)) /* 800x600/4 (VESA) */
goto no_vga;
For a while I was chasing a presumption that
arch/x86/kernel/setup.c::setup_arch() was enabling EFI support with
efi_enabled=1;
After a lot of analysis of boot_params.efi_info I arrived at the
"novga" code and realised it can also be triggered by the boot-loader
leaving the display in a graphic mode.
I then investigated the GRUB configuration and discovered the
GRUB_GFXPAYLOAD_LINUX option, described in the blueprint
https://blueprints.launchpad.net/ubuntu/+spec/packageselection-
foundations-n-grub2-boot-framebuffer
The bug can be fixed in "/etc/default/grub" by adding
GRUB_GFXPAYLOAD_LINUX=text
However, this is a local workaround. The blueprint refers to the file
"/boot/grub/gfxblacklist" which is generated by a script in the package
"grub-gfxpayload-lists". The file contains PCI IDs of video devices that
GRUB should not leave in graphics mode. These are declared in
"/usr/share/grub-gfxpayload-lists/blacklist/"
The attached patch adds a new file "20_intel" to the blacklisted devices
in the package.
If adding it manually to a system, place it in the "/usr/share/grub-
gfxpayload-lists/blacklist/" directory.
To add the new device to "/boot/grub/gfxblacklist.txt" run:
sudo update-grub-gfxpayload
** Patch added: "Blacklist Intel 815 devices from GRUB GFX handover"
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/907446/+attachment/2645278/+files/0001-LP907446-corrupt-consoles-on-Intel-i815-device.patch
** Also affects: grub-gfxpayload-lists (Ubuntu)
Importance: Undecided
Status: New
** Changed in: grub-gfxpayload-lists (Ubuntu)
Status: New => Confirmed
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https://bugs.launchpad.net/bugs/907446
Title:
Corrupt ttys, splash; Console colour dummy device
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