http://bugzilla.kernel.org/show_bug.cgi?id=13053
Summary: No HPET interrupts unless acpi_skip_timer_override is
set.
Product: ACPI
Version: 2.5
Kernel Version: 2.6.28
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: Config-Interrupts
AssignedTo: acpi_config-interru...@kernel-bugs.osdl.org
ReportedBy: w...@mit.edu
Regression: No
I'm in the process of qualifying Dell Optiplex 760 systems for Linux use at
MIT.
The target distribution will be Ubuntu 9.04.
When I boot the current snapshot of Ubuntu 9.04 (Jaunty) it seems like the
boot-up hangs. In reality, it seems that the HPET interrupts are not waking
the CPU from the C3 state.
If I boot with the default options and hit the power switch until the keyboard
gets initialized, and then press a key until the mouse support comes online,
and then if I move the mouse around I can generate interrupts that causes the
system to see the HPET interrupts and to function pretty much normally.
* If I boot with HPET=disable all seems well.
* If I go into the BIOS and disable C States (which disables the ability of
the CPU to enter the C3 energy saving state), all seems well.
* If I boot with the default HPET enabled and "acpi_skip_timer_override", all
seems well.
QUESTION:
What else should I be trying to further identify the root cause of this issue?
Are there finer grained or other interesting kernel options I should try?
I only got the clue about trying "acpi_skip_timer_override" by reviewing other
interrupt-related kernel bugs. The description of that parameter in the
kernel-parameters doc, "Recognize and ignore IRQ8/pin2 Interrupt Override. For
broken nForce2 BIOS resulting in XT-PIC timer." didn't make sense to me, but
surprisingly it did enable HPET operation and got the CPU out of C3.
I ran powertop and watched it behave a bit strangely when I was hand-creating
interrupts.
I was getting some very bizarre behavior under earlier kernels (because I was
first testing under Ubuntu 8.10.) But taking a very new beta of Ubuntu 9.04
the symptom got much simpler to describe. (Ubuntu 9.04 with kernel
2.6.28-11.37 seems to have incorporated pretty much every upstream HPET-related
patch from 2.6.29 that I could find in the kernel.org git repository.)
In the Ubuntu community, I am working this bug in Launchpad 348694:
https://bugs.launchpad.net/bugs/348694
The folks there suggested I raise the issue in a bugzilla in kernel.org by way
of getting clues from others more familiar with ACPI, HPET, and CPU State C3
lore.
I am grateful for any further insights.
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