Page flipping on intel (2.11 driver)

[Owen Taylor]

With the 2.11 update for xorg-x11-drv-intel in updates-testing we have a
couple of serious problems occurring with gnome-shell on Intel systems:

 A) A complete hang where the system can't even be pinged.

 B) A problem where the system continues to run fine but the GPU gets
    "stuck" and no further drawing happens until the system is rebooted.

We've also had similar reports for Compiz.

These problems seem to be associated in particular with the "page
flipping" functionality that it enables. (The implementation is mostly
in the kernel, but the use is driven by the X server.)

With considerable testing and experimentation, the biggest source of
hangs on my GMA3100 system turned out to be fixed by the kernel patch:

http://lists.freedesktop.org/archives/intel-gfx/2010-April/006463.html

However, that fix is "gen3" specific (i915, i945, and variants),
and we've also had reports of hard locks on newer chips like the i965
and GM45, so it's probably not the only thing going on. The second
problem also is likely unrelated.

My feeling is that we should disable page flipping for F13 - it's had
only a tiny bit of testing, and any fixes we put in at this point are
going to get a far tinier bit of testing.

We could "disable" it by simply avoiding pushing the 2.11 update, but
since that leaves things broken for people who have updates-testing
enabled, I think it would be better to patch the functionality out the
2.11 package. See the patch im:

 https://bugs.freedesktop.org/show_bug.cgi?id=27883#c3

for how to do that schematically, though it would be better to also
change the:

  "Kernel page flipping support detected, enabling"

message. (It would be sort of neat to have some way to allow users to
enable it and test, but maybe the "way to enable it" is just installing
the F-14 rawhide package.)

What do people think?

- Owen