Re: [PATCH 4/5] Centralise NO_IRQ definition

[Matthew Wilcox <matthew@wil.cx>]

On Mon, Nov 21, 2005 at 11:27:05AM -0800, Linus Torvalds wrote:
> On Mon, 21 Nov 2005, Matthew Wilcox wrote:
> >
> > On Mon, Nov 21, 2005 at 10:55:24AM -0800, Linus Torvalds wrote:
> > > Quite frankly, if we change [PCI_]NO_IRQ to -1, there's almost certainly 
> > > going to be a lot of drivers breaking.
> > 
> > There's only one driver using NO_IRQ today (outside of architectures
> > which define NO_IRQ to -1, that is).  So *this* series of patches should
> > break nothing.
> 
> Right. But the point is that most drivers will do something like
> 
> 	if (!dev->irq)
> 		return;
> 
> (whatever, made up). And that having NO_IRQ be anything but 0 is thus 
> fundamentally broken.

The idea was to give them something better to use instead of this.
Whether that be if (has_irq(dev)) return; or some other similar
construct, I'm not terribly fussed.

> I'm NOT talking about PCI specs.
> 
> I'm talking about real hardware.
> 
> Read pretty much _any_ data-sheet for an interrupt router, and you'll see 
> that the bit pattern 0000 means _disabled_. 

The only relevant thing I found with google was
http://www.microsoft.com/whdc/archive/pciirq.mspx

Where it talks about 0 meaning disabled, it says:

	Link Value for INTn#:A value of zero means this interrupt pin is
	not connected to any other interrupt pins and is not connected
	to any of the Interrupt Router's interrupt pins.

which is a different bit from where it talks about the AT-compatible
IRQ numbers.

Everything else I find seems to be talking about Arcnet hardware (!)
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