Date: Mon, 15 Jun 2009 00:12:07 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: "Hans J. Koch" <hjk@linutronix.de>
Cc: Wolfram Sang <w.sang@pengutronix.de>, linux-kernel@vger.kernel.org,
       linuxppc-dev@ozlabs.org, devicetree-discuss@ozlabs.org,
       Magnus Damm <magnus.damm@gmail.com>, "Hans J. Koch" <hjk@linutronix.de>,
       Greg KH <gregkh@suse.de>
Subject: Re: [PATCH 2/2] uio: add an of_genirq driver
Message-ID: <20090615001207.1829e7b5@lxorguk.ukuu.org.uk>
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> > +	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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