Re: [PATCH 4/5] Centralise NO_IRQ definition

[Linus Torvalds <torvalds@osdl.org>]

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.

Because the fact is, NO_IRQ _is_ zero. And exactly because it's zero, and 
that is encoded everywhere, nobody uses it.

> That's a common misreading of the PCI spec -- it actually says the
> opposite.

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_. 

In other words, I'm talking about HARD REALITY.

I know, it's a bitch.

		Linus
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