Re: XT-PIC interrupts blocked by usbserial ? [Was Re: Intel ICH9M bug : sata unusable with usbserial]

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On Thu, 3 Mar 2011, Mark Lord wrote:

> Okay, dug out a UHCI 1.1 spec, and the indication from there
> is that uhci_irq() can return IRQ_HANDLED in some cases where IRQ_NONE
> is more appropriate.

What cases are those?

> Also, it is not masking the "Reserved" bits from the status register.
> Presumably most implementations "read zero" for those bits,
> but perhaps not all do.

Perhaps not, but I've never come across one that does.  This
essentially amounts to saying that the only reasons a UHCI controller
generates an interrupt request are the documented ones.

Suppose the driver did mask out the reserved bits and return IRQ_NONE 
when none of the defined bits were set.  An implementation that did set 
one of the reserved bits would then create an interrupt storm.

> Dunno if this is the cause the XT-PIC errors from earlier in this thread though.

It seems most unlikely.  If the driver had a bug like that, it would 
have shown up many years ago.

Alan Stern

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