Re: 2.6.18-mm2

From: Mark Rustad
Date: Sat Sep 30 2006 - 13:21:13 EST

On Sep 30, 2006, at 11:21 AM, Matthew Wilcox wrote:

On Sat, Sep 30, 2006 at 10:26:22AM -0500, James Bottomley wrote:
On Fri, 2006-09-29 at 23:50 +0000, Frederik Deweerdt wrote:
+ if (!pdev->irq)
+ return -ENODEV;

Don't I remember that 0 is a valid IRQ on some platforms?

i.e. shouldn't this be

if (pdev->irq == NO_IRQ)
return -ENODEV;


I think this won't quite work because only the platforms that actually
have a valid zero irq define it, but there must be something else that

Linus threw a hissy fit and declared that platforms which use 0 as a
valid IRQ are broken and wrong. Despite PCI using 255 to mean no IRQ
and 0 as a valid IRQ ;-)

Having gone down the path of creating a platform that had IRQ 0 as a valid interrupt some time ago with the 2.4 kernel, all I can say is that while it can be made to work, things go much more smoothly if you don't use IRQ 0. Every driver added to the environment pretty much had to be tweaked. Of course that mainly meant adding to the #ifdef's that were already there for other architectures that had also made that mistake.

The biggest pain is admitting the mistake (of using IRQ 0) and changing it. Making a clear statement on the issue will help prevent others from making the same mistake again. I know that I wish that I had known not to do that from the beginning. Having been there and done that, I don't need any convincing.

Mark Rustad, MRustad@xxxxxxx

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