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

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Message-ID: <20090615094449.04b029f0@lxorguk.ukuu.org.uk>
Date:	Mon, 15 Jun 2009 09:44:49 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	"Hans J. Koch" <hjk@...utronix.de>
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

> 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?

The natural C way to write "No xxx" is if (!xxx) hence

	if (!dev->irq) {
		polling_start();
		return 0;
	}

The PC "IRQ 0" is the timer - which only appears in the arch code.

Alan
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