Re: [PATCH] synchronize_irq needs a barrier

quoted

 - even when you ignore the interrupt (because the driver doesn't care, 
   it's suspending), you need to make sure the hardware gets shut up by 
   reading (or writing) the proper interrupt status register.

   Otherwise, with a level interrupt, the interrupt will continue to be 
   held active ("screaming") and the CPU will get interrupted over and 
   over again, until the irq subsystem will just turn the irq off 
   entirely.

His suspend routine wrote to the IRQ mask (or equivalent) register in
his code example, thus the HW should shut up eventually, thus that isn't
strictly necessary, the IRQ in that case is just a "short
interrupt" (noticed by the PIC and delivered but possibly not asserted
anymore at this stage or about to go down).

In fact, he -must not- ack it. Because is the HW is really down (in D3),
got knows what accessing the ACK register will do. I can give you
ideas... from nothing on most x86 desktops to machine checks on most
powerpc machines, though I could imagine some cards bad enough to lock
your bus up if you try to access a register while they are in D3 (I've
seen some of those critters and it seems not all bridges timeout on
cards that just keep sending retries).

Cheers,
Ben.