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

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Date:	Mon, 15 Jun 2009 01:45:46 +0200
From:	"Hans J. Koch" <hjk@...utronix.de>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	"Hans J. Koch" <hjk@...utronix.de>,
	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>,
	Greg KH <gregkh@...e.de>
Subject: Re: [PATCH 2/2] uio: add an of_genirq driver

On Mon, Jun 15, 2009 at 12:12:07AM +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.

The above uioinfo->irq is a signed long.

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

It doesn't. It won't complain about IRQ 0 and will pass it on to
request_irq, which will probably fail if it is as you say.

I did it that way because I saw IRQ 0 in /proc/interrupts on every PC...

> 
> 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.

Funny.

> This was
> decided some years ago and a large part of the kernel simply doesn't
> support any notion of a real IRQ 0.

Can you tell me the reason for that decision or point me to some ml archive?

Thanks,
Hans

> 
> Alan
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