linux-kernel - Re: [PATCH 2/2] uio: add an of

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Date:	Mon, 15 Jun 2009 00:12:07 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	"Hans J. Koch" <hjk@...utronix.de>
Cc:	Wolfram Sang <w.sang@...gutronix.de>, linux-kernel@...r.kernel.org,
	linuxppc-dev@...abs.org, devicetree-discuss@...abs.org,
	Magnus Damm <magnus.damm@...il.com>,
	"Hans J. Koch" <hjk@...utronix.de>, Greg KH <gregkh@...e.de>
Subject: Re: [PATCH 2/2] uio: add an of_genirq driver

> > +	if (!uioinfo->irq)
> > +		uioinfo->irq = UIO_IRQ_NONE;
> 
> Please don't do this. It's inconsistent if all other UIO drivers require
> people to use UIO_IRQ_NONE and you also allow zero. UIO_IRQ_NONE was
> introduced because 0 may be a legal interrupt number on some platforms.

Zero is not a valid IRQ number in the kernel (except in arch specific
depths). IRQ numbers are also *unsigned* so -1 isn't a safe definition.

Zero means no IRQ. If any old UIO code is assuming otherwise it wants
fixing.

It is the job of the platform to map a physical IRQ 0 to some other
representation if it exists outside of arch specific code. This was
decided some years ago and a large part of the kernel simply doesn't
support any notion of a real IRQ 0.

Alan
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