Messages in this thread | | | From | Benjamin Herrenschmidt <> | Subject | Re: Question about IRQ_PENDING/IRQ_REPLAY | Date | Sun, 4 Mar 2001 13:36:40 +0100 |
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>In particular, if an edge-triggered interrupt comes in on an x86 IO-APIC >while that interrupt is disabled, enabling the interrupt will have caused >that irq to get dropped. And if it gets dropped, it will never ever happen >again: the interrupt line is now active, and there will never be another >edge again.
Ok, I see. We have a different issue with the old Apple IRQ controller that can lose interrupts if they are active when re-enabled. We currently rely on a hack to work aroud this that may re-send interrupts, but that involves hacking into __sti() to check for lost interrupts, which is bad.
Basically, even a level interrupt, if active while re-enabled, will not be sent by the pic to the CPU, and so further interrupts will be blocked too. We have some code in enable_irq() that can detect this case, but re-triggering the interrupt is not really simple and requires the __sti() hack for now.
I beleive we may have a way to re-trigger the interrupt without having to hack __sti() by using a fake timer interrupt. I'll look into this, but in that case, the code can be mostly self-contained in enable_irq, we will probably not need to play with IRQ_PENDING & IRQ_REPLAY flag at all.
>> I'd be glad if you could take the time to enlighten me about this as I'm >> trying to make the PPC code as close as the i386, according to your >> comment stating that it would be generic in 2.5, and I don't like having >> code I don't fully understand ;) > >You likely don't have this problem at all. Most sane interrupt controllers >are level-triggered, and won't show the problem. And others (like the >i8259) will see a disabled->enabled transition as an edge if the interrupt >is active (ie they have the edge-detection logic _after_ the disable >logic), and again won't have this problem.
Well, Apple now uses OpenPICs, but all slightly older macs had a home-made Apple controller that had the above issue :( In fact, it can happpen with both and and level interrupts for us.
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