RE: [SOLVED ??] Kernel 2.6.12 + IO-APIC + uhci_hcd = Trouble

RE: [SOLVED ??] Kernel 2.6.12 + IO-APIC + uhci_hcd = Trouble

[Protasevich, Natalie]

> Le Lundi 11 Juillet 2005 20:36, Alan Stern a écrit :
> > It's also possible that the UHCI controllers are generating the 
> > unwanted interrupt requests.  You should make sure that Legacy USB 
> > Support is turned off in your BIOS settings.
> 
> My motherboard both holds USB 1.1 and USB 2.0 controllers. I 
> don't have a "Legacy USB Support" option in my BIOS, all my 
> USB options are the following:
> 
> Enable USB 1.1 controller: YES	(Surely relates to my 
> true USB 1.1 controller)
> 
> Enable USB 2.0 controller: YES	(Same for the high 
> speed controller ?)
> 
> Enable USB keyboard: NO
> 
> Enable USB mouse support: YES	(Well, I have one ;-)
> 
> I didn't change anything regarding these so far.
> 
> > You can also try adding the "usb-handoff" kernel parameter to your 
> > boot command line.
> 
> Hey !! This one looks like the MIRACLE-OPTION !!

Alexander, should you try this option? (Just in case if you haven't noticed this thread)...

> I just booted using my 2.6.12 kernel patched with Nathalie's 
> patches (don't know if they help in there...) and the problem 
> seems to be gone !

Michel, it would be interesting to see if you have problems with the kernel that doesn't have the fix posted in that bugzilla yet, but only has my first patch.
 
> Nothing complains anymore about the interrupt. I have:
> 
> [root@totor etc]# cat /proc/interrupts
>            CPU0
>   0:     934501    IO-APIC-edge  timer
>   1:       4611    IO-APIC-edge  i8042
>   2:          0          XT-PIC  cascade
>   4:       2779    IO-APIC-edge  serial
>   7:          3    IO-APIC-edge  parport0
>  14:       7909    IO-APIC-edge  ide4
>  15:       7918    IO-APIC-edge  ide5
>  16:      38447   IO-APIC-level  nvidia
>  18:       2982   IO-APIC-level  eth0, eth1
>  19:      37041   IO-APIC-level  ide0, ide1, ide2, ide3, ehci_hcd:usb4
>  21:      52036   IO-APIC-level  uhci_hcd:usb1, 
> uhci_hcd:usb2, uhci_hcd:usb3
>  22:       2850   IO-APIC-level  VIA8233
> NMI:          0
> LOC:     934453
> ERR:          0
> MIS:          0
> 
> 
> ...now let's see with time if this is stable...
> 
> A thousand thanks for your suggestion Alan !
>
 
Thank you Alan! You helped me too, since my patch has broken a couple VIA chips lately. Now I know that at least the fix works...

 

Re: [SOLVED ??] Kernel 2.6.12 + IO-APIC + uhci_hcd = Trouble

[Michel Bouissou]

Le Lundi 11 Juillet 2005 21:52, Protasevich, Natalie a écrit :
>
> Michel, it would be interesting to see if you have problems with the kernel
> that doesn't have the fix posted in that bugzilla yet, but only has my
> first patch.

Do you mean the patch 
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=c434b7a6aedfe428ad17cd61b21b125a7b7a29ce
alone ?

I'll try to compile a kernel this way tomorrow, it's a bit late tonight...

Furthermore, please tell me if there are risks that I seriously break let's 
say my IDE devices interrupts doing this?
I use EVMS software RAID-5, and I don't want any problem with my RAID-5 set 
(I'm just out of some that took me hours...) especially because the EVMS 
snapshots I use for performing backups don't work anymore (I mean: are 
horribly broke) since I upgraded to a 2.6 series kernel.

This is quite another file, but just to explain that I don't have any recent 
and reliable backup these days, not time for me to take any unnecessary risk 
with my RAID-5 set until this gets fixed...

> Thank you Alan! You helped me too, since my patch has broken a couple VIA
> chips lately. Now I know that at least the fix works...

Well, that's what I'm worried about ;-))

Anyway, here are the differences I already noticed with and without your two 
patches, regarding the way the interrupts are distributed:

1/ Without your patches	(from an old note I took) :

[root@totor etc]# cat /proc/interrupts
           CPU0
  0:     626375    IO-APIC-edge  timer
  1:       1599    IO-APIC-edge  i8042
  2:          0          XT-PIC  cascade
  4:       1708    IO-APIC-edge  serial
  7:          2    IO-APIC-edge  parport0
 14:      19858    IO-APIC-edge  ide2
 15:       5220    IO-APIC-edge  ide3
 16:      30711   IO-APIC-level  nvidia
 18:       1799   IO-APIC-level  eth0, eth1
 19:     103365   IO-APIC-level  ide0, ide1, ehci_hcd:usb4, aic7xxx
 21:      47273   IO-APIC-level  uhci_hcd:usb1, uhci_hcd:usb2, uhci_hcd:usb3
 22:       2782   IO-APIC-level  VIA8233

(I've removed an SCSI controller and added another 2-channel IDE controller 
between the 2 outputs)

2/ With your 2 patches :

> > [root@totor etc]# cat /proc/interrupts
> >            CPU0
> >   0:     934501    IO-APIC-edge  timer
> >   1:       4611    IO-APIC-edge  i8042
> >   2:          0          XT-PIC  cascade
> >   4:       2779    IO-APIC-edge  serial
> >   7:          3    IO-APIC-edge  parport0
> >  14:       7909    IO-APIC-edge  ide4
> >  15:       7918    IO-APIC-edge  ide5
> >  16:      38447   IO-APIC-level  nvidia
> >  18:       2982   IO-APIC-level  eth0, eth1
> >  19:      37041   IO-APIC-level  ide0, ide1, ide2, ide3, ehci_hcd:usb4
> >  21:      52036   IO-APIC-level  uhci_hcd:usb1,
> > uhci_hcd:usb2, uhci_hcd:usb3
> >  22:       2850   IO-APIC-level  VIA8233
> > NMI:          0
> > LOC:     934453
> > ERR:          0
> > MIS:          0

Cheers.

-- 
Michel Bouissou <michel@bouissou.net> OpenPGP ID 0xDDE8AC6E

La Marseillaise sera d'autant moins sifflée qu'elle sera entonnée par tous.
	-- Raffoirius, Premier Ministre

Re: [SOLVED ??] Kernel 2.6.12 + IO-APIC + uhci_hcd = Trouble

[Alexander Fieroch]

Protasevich, Natalie wrote:
>>>You can also try adding the "usb-handoff" kernel parameter to your 
>>>boot command line.
>>
> Alexander, should you try this option? (Just in case if you haven't noticed this thread)...

Hm, no. All errors still occur. :-(

Regards,
Alexander

Re: Kernel 2.6.12 + IO-APIC + uhci_hcd = Trouble

[Alan Stern]

On Mon, 11 Jul 2005, Michel Bouissou wrote:

> Hi Nathalie,
> 
> Thanks for your answer and pointer. Unfortunately it doesn't help.
> 
> The patch you mention won't apply on my kernel alone, I need first to apply 
> the patch from 
> http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=c434b7a6aedfe428ad17cd61b21b125a7b7a29ce , 
> then your patch applies OK.
> 
> Unfortunately, it doesn't solve my issue. Booting this kernel still results in 
> an interrupt issue with uhci_hcd.
> 
> After boot, "cat /proc/interrupts" shows:
>            CPU0
>   0:     188066    IO-APIC-edge  timer
>   1:        308    IO-APIC-edge  i8042
>   2:          0          XT-PIC  cascade
>   4:        413    IO-APIC-edge  serial
>   7:          3    IO-APIC-edge  parport0
>  14:       1177    IO-APIC-edge  ide4
>  15:       1186    IO-APIC-edge  ide5
>  18:       1028   IO-APIC-level  eth0, eth1
>  19:       8513   IO-APIC-level  ide0, ide1, ide2, ide3, ehci_hcd:usb4
>  21:     100000   IO-APIC-level  uhci_hcd:usb1, uhci_hcd:usb2, uhci_hcd:usb3
>  22:          0   IO-APIC-level  VIA8233
> NMI:          0
> LOC:     187967
> ERR:          0
> MIS:          0
> 
> (The problem is with IRQ 21 for uhci_hcd)
> 
> (It is to note that without those patches, I didn't see any IRQ managed by 
> "XT-PIC", all were managed by the IO-APIC...)

It's possible that the errors you're getting are caused by some other
device erroneously generating interrupt requests on IRQ 21.  Then when
uhci-hcd enables that IRQ, there's no driver available to handle the 
interrupts...

It's also possible that the UHCI controllers are generating the unwanted 
interrupt requests.  You should make sure that Legacy USB Support is 
turned off in your BIOS settings.  You can also try adding the 
"usb-handoff" kernel parameter to your boot command line.

Alan Stern

Re: [SOLVED ??] Kernel 2.6.12 + IO-APIC + uhci_hcd = Trouble

[Michel Bouissou]

Le Lundi 11 Juillet 2005 20:36, Alan Stern a écrit :
> It's also possible that the UHCI controllers are generating the unwanted
> interrupt requests.  You should make sure that Legacy USB Support is
> turned off in your BIOS settings.

My motherboard both holds USB 1.1 and USB 2.0 controllers. I don't have a 
"Legacy USB Support" option in my BIOS, all my USB options are the following:

Enable USB 1.1 controller: YES	(Surely relates to my true USB 1.1 controller)

Enable USB 2.0 controller: YES	(Same for the high speed controller ?)

Enable USB keyboard: NO

Enable USB mouse support: YES	(Well, I have one ;-)

I didn't change anything regarding these so far.

> You can also try adding the "usb-handoff" kernel parameter to your boot
> command line. 

Hey !! This one looks like the MIRACLE-OPTION !!

I just booted using my 2.6.12 kernel patched with Nathalie's patches (don't 
know if they help in there...) and the problem seems to be gone !

Nothing complains anymore about the interrupt. I have:

[root@totor etc]# cat /proc/interrupts
           CPU0
  0:     934501    IO-APIC-edge  timer
  1:       4611    IO-APIC-edge  i8042
  2:          0          XT-PIC  cascade
  4:       2779    IO-APIC-edge  serial
  7:          3    IO-APIC-edge  parport0
 14:       7909    IO-APIC-edge  ide4
 15:       7918    IO-APIC-edge  ide5
 16:      38447   IO-APIC-level  nvidia
 18:       2982   IO-APIC-level  eth0, eth1
 19:      37041   IO-APIC-level  ide0, ide1, ide2, ide3, ehci_hcd:usb4
 21:      52036   IO-APIC-level  uhci_hcd:usb1, uhci_hcd:usb2, uhci_hcd:usb3
 22:       2850   IO-APIC-level  VIA8233
NMI:          0
LOC:     934453
ERR:          0
MIS:          0


...now let's see with time if this is stable...

A thousand thanks for your suggestion Alan !

(Kernel 2.4 was working plain good without such a boot option, I didn't know 
it existed...)

(Please copy me on answers, as I'm not subscribed to the linux-kernel mailing 
list.)

Cheers.

-- 
Michel Bouissou <michel@bouissou.net> OpenPGP ID 0xDDE8AC6E

Re: [SOLVED ??] Kernel 2.6.12 + IO-APIC + uhci_hcd = Trouble

[Alan Stern]

On Mon, 11 Jul 2005, Michel Bouissou wrote:

> Le Lundi 11 Juillet 2005 20:36, Alan Stern a écrit :
> > It's also possible that the UHCI controllers are generating the unwanted
> > interrupt requests.  You should make sure that Legacy USB Support is
> > turned off in your BIOS settings.
> 
> My motherboard both holds USB 1.1 and USB 2.0 controllers. I don't have a 
> "Legacy USB Support" option in my BIOS, all my USB options are the following:
> 
> Enable USB 1.1 controller: YES	(Surely relates to my true USB 1.1 controller)
> 
> Enable USB 2.0 controller: YES	(Same for the high speed controller ?)
> 
> Enable USB keyboard: NO
> 
> Enable USB mouse support: YES	(Well, I have one ;-)

That's what I was talking about.  BIOS support for keyboard and mouse is
called "Legacy" support, because it emulates plain old non-USB AT-type 
devices.  I bet if you turned off the "Enable USB mouse support" option 
then everything would work.

> I didn't change anything regarding these so far.
> 
> > You can also try adding the "usb-handoff" kernel parameter to your boot
> > command line. 
> 
> Hey !! This one looks like the MIRACLE-OPTION !!
> 
> I just booted using my 2.6.12 kernel patched with Nathalie's patches (don't 
> know if they help in there...) and the problem seems to be gone !
> 
> Nothing complains anymore about the interrupt. I have:
> 
> [root@totor etc]# cat /proc/interrupts
>            CPU0
>   0:     934501    IO-APIC-edge  timer
>   1:       4611    IO-APIC-edge  i8042
>   2:          0          XT-PIC  cascade
>   4:       2779    IO-APIC-edge  serial
>   7:          3    IO-APIC-edge  parport0
>  14:       7909    IO-APIC-edge  ide4
>  15:       7918    IO-APIC-edge  ide5
>  16:      38447   IO-APIC-level  nvidia
>  18:       2982   IO-APIC-level  eth0, eth1
>  19:      37041   IO-APIC-level  ide0, ide1, ide2, ide3, ehci_hcd:usb4
>  21:      52036   IO-APIC-level  uhci_hcd:usb1, uhci_hcd:usb2, uhci_hcd:usb3
>  22:       2850   IO-APIC-level  VIA8233
> NMI:          0
> LOC:     934453
> ERR:          0
> MIS:          0
> 
> 
> ...now let's see with time if this is stable...
> 
> A thousand thanks for your suggestion Alan !

You're welcome.

> (Kernel 2.4 was working plain good without such a boot option, I didn't know 
> it existed...)

A lot has changed since 2.4... not always for the better!

Alan Stern

Re: [SOLVED ??] Kernel 2.6.12 + IO-APIC + uhci_hcd = Trouble

[Michel Bouissou]

Le Lundi 11 Juillet 2005 21:43, Alan Stern a écrit :
> >
> > Enable USB mouse support: YES	(Well, I have one ;-)
>
> That's what I was talking about.  BIOS support for keyboard and mouse is
> called "Legacy" support, because it emulates plain old non-USB AT-type
> devices.  I bet if you turned off the "Enable USB mouse support" option
> then everything would work.

Aha. And what would be your advice ? Rather leave the BIOS mouse option ON and 
use "usb-handoff", or remove both ?

I'll check without both tomorrow anyway, it's a bit late tonight for keeping 
on breaking the machine ;-)

> > A thousand thanks for your suggestion Alan !
>
> You're welcome.

Well, you really deserve my thanks :-)

> A lot has changed since 2.4... not always for the better!

Hmmm... I've seen... 2.6.12 is the first release that seems to be willing to 
work on my system -- with some tweaking, coffee and aspirin. Previous 2.6.x 
releases I had tried (2.6.3, 2.6.6) were horribly broken on my poor VIA 
hardware ;-)

Cheers.

-- 
Michel Bouissou <michel@bouissou.net> OpenPGP ID 0xDDE8AC6E

Re: [SOLVED ??] Kernel 2.6.12 + IO-APIC + uhci_hcd = Trouble

[Alan Stern]

On Mon, 11 Jul 2005, Michel Bouissou wrote:

> Le Lundi 11 Juillet 2005 21:43, Alan Stern a écrit :
> > >
> > > Enable USB mouse support: YES	(Well, I have one ;-)
> >
> > That's what I was talking about.  BIOS support for keyboard and mouse is
> > called "Legacy" support, because it emulates plain old non-USB AT-type
> > devices.  I bet if you turned off the "Enable USB mouse support" option
> > then everything would work.
> 
> Aha. And what would be your advice ? Rather leave the BIOS mouse option ON and 
> use "usb-handoff", or remove both ?

Well, some people don't have a choice.  They need to leave BIOS USB 
keyboard/mouse support turned on in order to use their USB keyboard/mouse 
before the Linux kernel has loaded (within Grub, for instance).

If you don't care about that, then it's cleaner to turn off the BIOS 
support.  Of course, you may find that you still need to use 
"usb-handoff" anyway!

In the end it doesn't make much difference.  Do whatever works best for 
you.

Alan Stern

Re: [SOLVED ??] Kernel 2.6.12 + IO-APIC + uhci_hcd = Trouble

[Michel Bouissou]

Le Lundi 11 Juillet 2005 22:16, Alan Stern a écrit :
> > Aha. And what would be your advice ? Rather leave the BIOS mouse option
> > ON and use "usb-handoff", or remove both ?
>
> Well, some people don't have a choice.  They need to leave BIOS USB
> keyboard/mouse support turned on in order to use their USB keyboard/mouse
> before the Linux kernel has loaded (within Grub, for instance).
>
> If you don't care about that, then it's cleaner to turn off the BIOS
> support.  Of course, you may find that you still need to use
> "usb-handoff" anyway!

Well, I'm afraid I spoke too fast :-(

I rebooted my system with "usb-handoff" again, but still the USB mouse enabled 
in BIOS, and this time got the punishent again :-(

usbcore: registered new driver usbfs
usbcore: registered new driver hub
USB Universal Host Controller Interface driver v2.2
PCI: Via IRQ fixup for 0000:00:10.0, from 10 to 5
uhci_hcd 0000:00:10.0: VIA Technologies, Inc. VT82xxxxx UHCI USB 1.1 
Controller
uhci_hcd 0000:00:10.0: new USB bus registered, assigned bus number 1
uhci_hcd 0000:00:10.0: irq 21, io base 0x0000cc00
hub 1-0:1.0: USB hub found
hub 1-0:1.0: 2 ports detected
PCI: Via IRQ fixup for 0000:00:10.1, from 10 to 5
uhci_hcd 0000:00:10.1: VIA Technologies, Inc. VT82xxxxx UHCI USB 1.1 
Controller (#2)
uhci_hcd 0000:00:10.1: new USB bus registered, assigned bus number 2
uhci_hcd 0000:00:10.1: irq 21, io base 0x0000d000
hub 2-0:1.0: USB hub found
hub 2-0:1.0: 2 ports detected
PCI: Via IRQ fixup for 0000:00:10.2, from 10 to 5
uhci_hcd 0000:00:10.2: VIA Technologies, Inc. VT82xxxxx UHCI USB 1.1 
Controller (#3)
usb 1-1: new low speed USB device using uhci_hcd and address 2
uhci_hcd 0000:00:10.2: new USB bus registered, assigned bus number 3
uhci_hcd 0000:00:10.2: irq 21, io base 0x0000d400
hub 3-0:1.0: USB hub found
hub 3-0:1.0: 2 ports detected
PCI: Via IRQ fixup for 0000:00:10.3, from 11 to 3
ehci_hcd 0000:00:10.3: VIA Technologies, Inc. USB 2.0
ehci_hcd 0000:00:10.3: new USB bus registered, assigned bus number 4
ehci_hcd 0000:00:10.3: irq 19, io mem 0xe3009000
ehci_hcd 0000:00:10.3: USB 2.0 initialized, EHCI 1.00, driver 10 Dec 2004
usbcore: registered new driver hiddev
hub 4-0:1.0: USB hub found
hub 4-0:1.0: 6 ports detected
usbhid: probe of 1-1:1.0 failed with error -5
usbcore: registered new driver usbhid
drivers/usb/input/hid-core.c: v2.01:USB HID core driver
irq 21: nobody cared!

...etc :-(

Well, this time, I deactivated the mouse in BIOS, rebooted again, also with 
"usb-handoff", and "again it works"...

-- 
Michel Bouissou <michel@bouissou.net> OpenPGP ID 0xDDE8AC6E

Re: [SOLVED ??] Kernel 2.6.12 + IO-APIC + uhci_hcd = Trouble

[Michel Bouissou]

Le Lundi 11 Juillet 2005 22:46, Michel Bouissou a écrit :
>
> Well, this time, I deactivated the mouse in BIOS, rebooted again, also with
> "usb-handoff", and "again it works"...

...at least, it worked until I unplugged my USB scanner...

Jul 11 22:52:54 totor kernel: usb 3-2: USB disconnect, address 2

...then replugged my USB scanner...

Jul 11 22:53:08 totor kernel: usb 3-2: new full speed USB device using 
uhci_hcd and address 3
Jul 11 22:53:08 totor kernel: irq 21: nobody cared!

Oh no :-(

-- 
Michel Bouissou <michel@bouissou.net> OpenPGP ID 0xDDE8AC6E

Re: [SOLVED ??] Kernel 2.6.12 + IO-APIC + uhci_hcd = Trouble

[Alan Stern]

On Mon, 11 Jul 2005, Michel Bouissou wrote:

> Well, I'm afraid I spoke too fast :-(
> 
> I rebooted my system with "usb-handoff" again, but still the USB mouse enabled 
> in BIOS, and this time got the punishent again :-(

> irq 21: nobody cared!
> 
> ...etc :-(
> 
> Well, this time, I deactivated the mouse in BIOS, rebooted again, also with 
> "usb-handoff", and "again it works"...

> ...at least, it worked until I unplugged my USB scanner...
>
> Jul 11 22:52:54 totor kernel: usb 3-2: USB disconnect, address 2
>
> ...then replugged my USB scanner...
>
> Jul 11 22:53:08 totor kernel: usb 3-2: new full speed USB device using
> uhci_hcd and address 3
> Jul 11 22:53:08 totor kernel: irq 21: nobody cared!
>
> Oh no :-(

Don't jump to hasty conclusions.  Problems like this are often caused by
unrelated things that you wouldn't suspect at first.  Getting something to
work once doesn't mean the problem has been fixed.  And you can be fooled
by coincidences.  (I would be surprised if that event above was really 
caused by plugging in the scanner, unless your UHCI hardware is broken.)

One thing you might try, time-consuming though it will be, is to remove or
disable as much hardware as possible from your system.  If you can
reliably determine that the problem occurs only when one particular piece
of hardware is enabled, then you'll know how to proceed.

Alan Stern

Re: [SOLVED ??] Kernel 2.6.12 + IO-APIC + uhci_hcd = Trouble

[Michel Bouissou]

Le Lundi 11 Juillet 2005 23:21, Alan Stern a écrit :
> Don't jump to hasty conclusions.  Problems like this are often caused by
> unrelated things that you wouldn't suspect at first.

I know... Been working with computers for... Uh... 25 years ?

> Getting something to work once doesn't mean the problem has been fixed.

That's so sadly right ;-)

> And you can be fooled by coincidences.  (I would be surprised if that event
> above was really caused by plugging in the scanner, unless your UHCI
> hardware is broken.) 

I don't believe the hardware is broken, as it's been running for more than 2 
years 100% stable with a 24/7/365 uptime. And with me plugging and unplugging 
USB devices...

Never had a single problem of the kind with any 2.4.x kernel. Get those 
problems only with 2.6.x kernels, and, in 2.6.12, only when UP IO-APIC is 
enabled (which ran perfectly good in 2.4).

So the problem is circled to 2.6 kernel, uhci_hcd and UP IO-APIC.

> One thing you might try, time-consuming though it will be, is to remove or
> disable as much hardware as possible from your system.  If you can
> reliably determine that the problem occurs only when one particular piece
> of hardware is enabled, then you'll know how to proceed.

I can hardly remove my VIA chipset from the mobo, and the USB thing is in the 
VIA thing ;-))

And I'm afraid I won't have the time to play that much with hardware, besides 
the fact that this is supposed to be a server which usually has uptimes over 
90 days rather than reboot-for-testing-the-damn-kernel-once-again ;-))

But I'm pretty sure this is no hardware problem, unless 2.6 considers "bad 
hardware" what 2.4 used to consider "nice hardware"...

Cheers.

-- 
Michel Bouissou <michel@bouissou.net> OpenPGP ID 0xDDE8AC6E

Re: [SOLVED ??] Kernel 2.6.12 + IO-APIC + uhci_hcd = Trouble

[Alan Stern]

On Mon, 11 Jul 2005, Michel Bouissou wrote:

> Le Lundi 11 Juillet 2005 23:21, Alan Stern a écrit :
> > Don't jump to hasty conclusions.  Problems like this are often caused by
> > unrelated things that you wouldn't suspect at first.
> 
> I know... Been working with computers for... Uh... 25 years ?

35 years for me...  My, how the time flies!

> I don't believe the hardware is broken, as it's been running for more than 2 
> years 100% stable with a 24/7/365 uptime. And with me plugging and unplugging 
> USB devices...
> 
> Never had a single problem of the kind with any 2.4.x kernel. Get those 
> problems only with 2.6.x kernels, and, in 2.6.12, only when UP IO-APIC is 
> enabled (which ran perfectly good in 2.4).
> 
> So the problem is circled to 2.6 kernel, uhci_hcd and UP IO-APIC.

Don't rule out the hardware too quickly.  2.4 and 2.6 manage the UHCI
controllers in different ways.  In particular, the usb-uhci driver in 2.4
does not suspend the controller when no devices are attached, whereas
uhci-hcd in 2.6 does.  (So does the "alternate" uhci driver in 2.4.)  I
recently handled a bug report -- from another Frenchman -- where it turned
out that his UHCI hardware instantly crashed the entire system whenever
it resumed from the suspended state!

To try and help pin things down, tomorrow (i.e., Tuesday) I'll send you a
test patch to completely disable the UHCI controllers, leaving them awake
and idle, not generating interrupts.  If you still get those spurious
IRQs, they will have to come from somewhere else.  (Assuming you can
devote server time to this sort of testing...)

And of course, if the spurious IRQs stop then we'll know where to probe 
further.

Alan Stern