Re: [PATCH] restore libata build on frv

From: Linus Torvalds
Date: Tue Sep 26 2006 - 12:17:27 EST

On Tue, 26 Sep 2006, David Woodhouse wrote:
> On Tue, 2006-09-26 at 04:52 -0400, Jeff Garzik wrote:
> > The irq is a special case no matter how we try to prettyify it. We need
> > two irqs, and PCI only gives us one per device.
> That's fine -- but don't use zero to mean none. We have NO_IRQ for that,
> and zero isn't an appropriate choice.

Zero _is_ an appropriate choice, dammit!

That NO_IRQ thing should be zero, and any architecture that thinks that
zero is a valid IRQ just needs to fix its own irq mapping so that the
"cookie" doesn't work.

The thing is, it's zero. Get over it. It can't be "-1" or some other
random value like people have indicated, because that thing is often read
from places where "-1" simply isn't a possible value (eg it gets its
default value initialized from a "unsigned char" in MMIO space on x86).

So instead of making everybody and their dog to silly things with some
NO_IRQ define that they haven't historically done, the rule is simple: "0"
means "no irq", so that you can test for it with obvious code like

if (!dev->irq)

and then, if your actual _hardware_ things that the bit-pattern with all
bits clear is a valid irq that can be used for normal devices, then what
you do is you add a irq number translation layer (WHICH WE NEED AND HAVE
_ANYWAY_) and make sure that nobody sees that on a _software_ level.

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