Re: [Qemu-devel] [PATCH] pci: Don't call pci_irq_handler() for a negative intx

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Sun, 2015-07-05 at 09:03 +0200, Michael S. Tsirkin wrote:
> On Sun, Jul 05, 2015 at 09:28:28AM +1000, Benjamin Herrenschmidt wrote:
> > Under some circumstances, pci_intx() can return -1 (when the interrupt
> > pin in the config space is 0 which normally means no interrupt).
> > 
> > I have seen cases of pci_set_irq() being called on such devices, in
> > turn causing pci_irq_handler() to be called with "-1" as an argument
> > which doesn't seem like a terribly good idea.
> > 
> > Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> 
> Isn't this a device bug though?

Possibly, I can try to dig a bit more see if I can reproduce and find
out who is causing it.

> I did a grep over all callers of pci_set_irq and didn't
> find any that fails to set an interrupt pin.
> 
> So how about an assert instead?
> 
> And maybe stick it in pci_intx to make sure all callers
> get checked.

Ok, It's also possible that this doesn't happen anymore, I've carried
that patch for monthes and rebased several times on top of newer qemu's.

I *think* it might have been something that happens due to some generic
code initializations, something like pci_update_irq_disabled() in
pci_default_write_config()... I'll dbl check.

Cheers,
Ben.