[Ubuntu-x-swat] [Bug 1168967] Re: regression: no video after upgrading kernel, mesa, libc, and several other packages (ThinkPad T500)

2013-04-17 Thread Greg Ward 
Workaround #1:

 I guess I'll repartition and try installing raring in the new
partition.

success! the bug has been fixed in Ubuntu 13.04. This is still an update
regression with 12.10; my ThinkPad T500 worked just fine on March 31 and
video stopped working on April 13. But at least the next version of
Ubuntu is not affected.

Workaround #2: boot Ubuntu 12.10 with kernel parameter nosetmode.
Success! I also removed quiet and splash from the kernel command
line, so I see a nice noisy boot process. X starts fine, and performance
is just fine. Text consoles appear to be plain old-fashioned text mode,
just like back in the old days before KMS. There is a tiny flicker
switching between text consoles and X, again just like in the old days.

Workaround #3: boot Ubuntu 12.10 with kernel parameter vga=0x0f00
(standard 80x25 text). Fails. I get the same noisy boot process as
before (again I have removed quiet and splash), in glorious black-
and-white 80x25 text. But the screen goes black after a while --
presumably when starting X?

Anyways, the evidence points to this being a bug in kernel mode setting,
so I'm changing the affected package.

** Package changed: xorg (Ubuntu) = linux (Ubuntu)

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Title:
  regression: no video after upgrading kernel, mesa, libc, and several
  other packages (ThinkPad T500)

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[Ubuntu-x-swat] [Bug 1168967] Re: regression: no video after upgrading kernel, mesa, libc, and several other packages (ThinkPad T500)

2013-04-16 Thread Greg Ward 
This is starting to look very much like a kernel bug, although I'm still
confused about several things. My main evidence is that I'm having
similar problems with System Rescue CD, a Gentoo-based rescue distro
that boots from CD or USB stick.

In particular, System Rescue CD 3.4.1 (kernel 3.4.32) works fine, but
System Rescue CD 3.4.2 (kernel 3.4.35) does not. Works fine means that
during boot, it switches from 80x25 text mode to high-res text mode just
fine -- I presume this is kernel video mode setting in action? But
System Rescue CD 3.4.2 fails that mode switch: the screen just goes
black. That's not the exact same manifestation as I'm seeing in Ubuntu,
but of course Ubuntu and System Rescue CD have different boot
procedures.

More data points:
  * if I boot System Rescue CD 3.4.2 (kernel 3.4.35) using its framebuffer 
console in high resolution option, everything is fine (although X is painfully 
slow)
  * if I boot System Rescue CD 3.4.2 using its alt kernel option (kernel 
3.7.10), everything works fine

Summary:
  * I'm seeing similar behaviour in two different distros (Ubuntu 12.10 and 
System Rescue CD 3.4.2)
  * I can dodge the bug with System Rescue CD either by a) using framebuffer 
console or b) booting a newer kernel
This makes me strongly suspect that it's a kernel bug, specifically related to 
kernel video mode setting.

The one thing that I don't understand: why is the bug still there if I
boot an older Ubuntu kernel, e.g. 3.5.0-26 or 3.5.0-21 rather than
3.5.0-27? Very strange.

It looks like there are no linux-image packages in quantal-backports, so
trying a newer kernel will be tricky. I guess I'll repartition and try
installing raring in the new partition.

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You received this bug notification because you are a member of Ubuntu-X,
which is subscribed to xorg in Ubuntu.
https://bugs.launchpad.net/bugs/1168967

Title:
  regression: no video after upgrading kernel, mesa, libc, and several
  other packages (ThinkPad T500)

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/xorg/+bug/1168967/+subscriptions

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