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SubjectRe: question on odd APIC behavior
On Fri, 16 Nov 2007, Oliver Neukum wrote:

> > > On irq 20, there's an UHCI, on irq 19 is an EHCI. For every interrupt on 20
> > > there's a spurious interrupt on 19. USB devices on bus of the controller on 20
> > > work. So I know all interrupts are seen. ERR does not increase. Interrupts
> > > for devices on the bus of the controller on 19 arrive at 19 only.
> >
> > I suggest you try to sort it out with the maintainers of the UHCI and
> > EHCI drivers then.
>
> They are innocent. This laptop really delivers an interrupt twice.

Perhaps, but these drivers are involved and the device-specific knowledge
will help tracking down the cause. I have general experience on how
interrupts work, including on APIC-based systems, but I have no idea how
UHCI and EHCI devices work in this area and, in particular, how you know
an interrupt coming from the line #19 is related to one on the line #20
and then a spurious one if not recorded as ERR or otherwise unclaimed
(which would be reported as "irq 19: nobody cared").

Maciej
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