Comment 137 for bug 311895

(In reply to comment #87)
> Then I tested all possible combinations of 2.6.31rc1 with/without this patch,
> with 1GB or 2 GB RAM, and with "
> early" or "late" loading of i915/drm.
>
> early: modules are contained and loaded by initramfs, i. e. pretty much as one
> of the first things after the k
> ernel starts to boot
>
> late: I booted without an initramfs, thus init starts readahead, sets the
> hostname and keyboard layout, and th
> en starts udev which does an "udev trigger" and causes modules such as drm and
> i915 to be loaded, which in tur
> n does KMS.

Sounds like a good set of combinations, thanks for testing.

> In earlier Karmic (2.6.30 release candidates), we didn't put i915/drm into the
> initramfs, and it worked fine (just looked a bit ugly since mode got switched
> halfway through boot). Now I noticed that this late loading doe
> s not work any more for some reason, not with 2.6.30 final, not with 31rc1, or
> with 31rc1+your patch. That is
> a bug in itself, and sounds pretty unrelated to this pipe underrun issue, so
> perhaps I should report it separately?

One thing jumped out between the early (working) and late (broken) logs: in the broken ones there's no line for the fbcon loading & initializing. Which would leave your display blank if/until X starts. Maybe that's missing from the load in the late case?

> Results from this testing:
> * late loading never works, I always get LVDS and DVI turned off
> * early loading works with .30 final and .31rc1 vanilla
> * with this patch applied, it never works, and worse, I don't even get a dmesg
> captured; this means that the
> boot doesn't even get to rcS/70. Sounds like it wedges display and causes a
> kernel panic? Anything I can do to
> debug this?
> * 1 GB/2 GB does not make any difference in any test case

Ugh, ok so it's probably not a pipe underrun then if it kills the whole machine (at least I hope not); could be a kernel panic. You could try netconsole (modprobe netconsole netconsole=<params> and then use nc on another machine, the kernel Documentation/ directory has some info on that); it might capture a panic if you load the module by hand with the netconsole running.