Btw, this is very much the case for MSI irq's in particular. If you ask to
_mask_ them, it will go to the look up the device list and try to mask
them (quite frankly, that sounds insane to me, but whatever), but that not
what the irq layer does for the simple "disable()" case.
It will literally just set the flag, and then even if an interrupt happens
afterwards, it will just ->ack it, and then call the ->end thing - and
doesn't need to do anything else in the whole "disable" path because MSI's
are obviously edge-triggered.
And the ACK is a pure (x2/io)apic thing, and again doesn't actually touch
the device itself, only the irq controller itself.
So while it is possible in theory that some irq controller ends up trying
to access the device for disable_irq, I don't think it's ever true in
reality.
But it's possible that I overlooked some really odd case, of course.
Linus
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