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

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Date:	Mon, 15 Jun 2009 19:45:39 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	"Hans J. Koch" <hjk@...utronix.de>, devicetree-discuss@...abs.org,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	Greg KH <gregkh@...e.de>
Subject: Re: [PATCH 2/2] uio: add an of_genirq driver

On Mon, 2009-06-15 at 00:12 +0100, Alan Cox wrote:
> > > +	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.

Right, and powerpc complies with that rule, so 0 is fine for us.

Cheers,
Ben.

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