Re: Reworking suspend-resume sequence (was: Re: PCI PM: Restore standard config registers of all devices early)

Linus Torvalds
2009-02-03T18:00:42Z

On Tue, 3 Feb 2009, Rafael J. Wysocki wrote:
>
> Having reconsidered it, I think that the "loop of disable_irq()" may be
> problematic due to MSI/MSI-X and devices that are put into D3 during the
> "normal" suspend. That is, we shouldn't try to mask MSI/MSI-X for devices in
> D3

Rafael, you seem to be confused about what "disable_irq()" does.

It does not touch the driver hardware AT ALL. It literally just touches
the interrupt controller, and even that only indirectly.

What disable_irq() does it literally:

void disable_irq_nosync(unsigned int irq)
{
struct irq_desc *desc = irq_to_desc(irq);
unsigned long flags;

if (!desc)
return;

spin_lock_irqsave(&desc->lock, flags);
if (!desc->depth++) {
desc->status |= IRQ_DISABLED;
desc->chip->disable(irq);
}
spin_unlock_irqrestore(&desc->lock, flags);
}

and then it does a "synchronize_irq()" to wait to make sure that there are
no pending ones.

And in many cases, even the

desc->chip->disable(irq);

doesn't actually _do_ anything - we'll quite possibly continue to take the
interrupt, and only when the interrupt happens will it see the "oh,
IRQ_DISABLED is set" thing, and do something about it.

So don't worry about putting devices in D3 - disable_irq() will not care
AT ALL whether the device is alive or not, and will never try to touch it
anyway.

Linus