** Description changed:
Binary package hint: usplash
Ubuntu 8.10
Linux 2.6.27-14-generic #1 SMP Wed Apr 15 18:59:16 UTC 2009
linux-image-2.6.27-14-generic, Version: 2.6.27-14.33
usplash, Version 0.5.25
After booting a recent kernel with usplash ("splash") and no frame
buffer ("nofb"), when using 512-character console fonts (like
Uni1-Fixed16), glyphs in the second half of the font are always
displayed highlighted (that is, bright white, not dull white). This can
best be seen by switching to the console immediately after booting and
running showconsolefont. (If you have not patched the kernel to fix the
font corruption issue with the 512-character fonts, you may need to
first run setfont Uni1-Fixed16 to see all of the characters.)
Some background: Normally, in text mode, the VGA hardware can only
display 256 unique characters, since only 8 bits are available for each
character in text memory. In order to display 512 unique characters, a
bit must be "stolen" from the attribute memory, which normally is used
for the character's foreground and background colors. The bit that is
"stolen" is normally used to define the brightness of the character's
foreground color. In fact, thanks to this bug, we see that it still can
affect the character's brightness even after it has been "stolen". In
order to get all 512 characters to be displayed at the same intensity,
the kernel clears a bit in the VGA's Color Plane Enable Register to
disable the corresponding bit plane. Now when a binary 1111 (bright
white) is passed to the color palette, only 0111 (dull white) gets
through.
At boot time, console-setup is run very early, even before usplash. If
the font loaded by console-setup is a 512-character font, the kernel
clears the necessary bit, as discussed above. Then usplash runs,
switches to a graphics mode, does its thing, then exits. When it exits
it puts the console back into text mode and restores the font to the VGA
memory, but it never restores the VGA registers. Most of the VGA
registers are set up fine, just by switching to text mode, but not the
one we are interested in here.
Oddly enough, usplash does save the VGA registers -- it just never
restores them. It did up until a few years ago, but that was changed.
I am including a couple of patches for consideration. Either one should fix
the problem. One patch, "restore_all_regs.patch", simply restores the code
that restores all of the VGA registers. The other patch,
"restore_cpe_reg.patch", restores only the Color Plane Enable Register -- the
one register that relates to this bug. I think the first patch is probably the
better patch, and could make usplash a little more robust by possibly
preventing other bugs from cropping up in the future due to registers that were
not restored. On the other hand, there is something to be said for making the
smallest change necessary to fix a bug, and thus reduce the chances of creating
others, which is why I've included the second patch.
This problem is mentioned by Uwe Geuder in a comment to LP:355057:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/355057/comments/12
Reports for other bugs that also happen to mention a similar problem which
may or may not be related to this bug:
https://bugs.launchpad.net/bugs/303561
https://bugs.launchpad.net/bugs/159053
Note that this problem does not occur when booting the 8.10 Live CD. This is
only because there was a problem with an initramfs script which prevented the
font from being loaded before usplash was run. That problem was fixed last
November. So you need a kernel newer than that to test this.
To reproduce:
1. grep CODESET /etc/default/console-setup
2. If CODESET is not a 512-character codeset (like Uni1, Uni2, or Uni3), run
sudo dpkg-reconfigure console-setup
to change it.
3. Ensure that the /boot/initrd... file that you boot with was the one that
was
updated by dpkg-reconfigure (it isn't always)
4. Boot using the nofb and splash options. (You have a recent kernel, right?)
5. Wait for system to fully boot up, then switch to a text console and log-in.
6. showconsolefont
7. Ignore the garbage between the columns of characters -- that's another bug.
8. If the 256 characters on the right are missing or trashed, run
setfont Uni1-Fixed16
- 9. If the 256 characters on the right are brighter than the 256 on the right,
+ 9. If the 256 characters on the right are brighter than the 256 on the left,
you have this bug.
--
Some characters always display highlighted on VGA console.
https://bugs.launchpad.net/bugs/392795
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