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Re: [Xen-devel] dom0 kernel - irq nobody cared ... the continuing saga ..

>>> On 10.02.15 at 11:47, <linux@xxxxxxxxxxxxxx> wrote:
> Tuesday, February 10, 2015, 11:36:48 AM, you wrote:
>> No - such a shared IRQ gets sent to both domains. There's no notion
>> of one domain claiming it and the other then not seeing it, as any
>> instance of the interrupt may mean more than one of the devices
>> signaled it - remember that shared interrupts are always level
>> triggered, i.e. there is no way of telling how many devices request
>> servicing.
> Ok .. just thinking out loud .. 
> But how would that work then ?
> If the interrupt gets always sent to both domains 
> and
> there is no handler for it in dom0
> Wouldn't that then *always* cause a "irq nobody cared" ..
> unless it's masked ? 

That's what the handler pciback installs is needed for.

> And if so .. wouldn't that imply that since i sometimes (but not always)
> get the "irq nobody cared", that it is unmasked at some point in time ? 

No, seeing this depends on both the other driver (some claim
they handled IRQs even if their device didn't need service) and
the rate at which "false" IRQs get sent.

> And if so .. is there a way to detect that it's get unmasked ?

IRQs without handlers are masked; when a handler gets installed
they get unmasked.


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