linux-kernel - Re: [patch] x86 supports NO

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Message-Id: <200806230429.36298.david-b@pacbell.net>
Date:	Mon, 23 Jun 2008 04:29:36 -0700
From:	David Brownell <david-b@...bell.net>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, hpa@...or.com
Subject: Re: [patch] x86 supports NO_IRQ convention

On Monday 23 June 2008, Alan Cox wrote:
> Zero is not a valid IRQ in the kernel mapping of things.

That's counter-factual:

           CPU0       CPU1       
  0:   42851354    6500253   IO-APIC-edge      timer
  1:     475459      45904   IO-APIC-edge      i8042
  8:          0          1   IO-APIC-edge      rtc0
  9:        135         18   IO-APIC-fasteoi   acpi
 12:    5232181     495206   IO-APIC-edge      i8042
 ...

That's on x86.  A quick survey of other boards around here
shows many that use IRQ 0 too.

I certainly agree it'd be convenient to be able to just test
for IRQ being nonzero.  Presumably only one driver would ever
end up using IRQ 0 on x86, so other drivers could ignore the
fact that testing for nonzero would mean "not the timer irq"
rather than "no irq assigned".

- Dave
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