linux-kernel - Re: [RFC] killing the NR

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Message-Id: <200702280141.51420.arnd@arndb.de>
Date:	Wed, 28 Feb 2007 01:41:50 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...e.de>, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC] killing the NR_IRQS arrays.

On Tuesday 27 February 2007, Eric W. Biederman wrote:
> * Add a variation of the API in interrupt.h that uses
>   "struct irq *irq" instead of "unsigned int irq"
>   
>   Probably replacing request_irq with irq_request or something
>   trivial like that.
> 
>   This will need to touch all of different irq implementation back
>   ends, but only very lightly.
> 
> * Convert the generic irq code to use struct irq * everywhere it
>   current uses "unsigned int irq".
> 
> * Start on the conversions of drivers and subsystems picking on
>   the easy ones first :)

Introducing the irq_request() etc. functions that take a struct irq*
instead of an int sounds good, but I'd hope we can avoid using those
in device drivers and do a separate abstraction for each bus_type
that deals with interrupts. I'm not sure if that's possible for
each bus_type, but the ones I have worked with in the past should
allow that:

pci: each device/function has a unique irq, drivers need not know
     about it afaics.
isa/pnp: numbers from 1 to 15 are the right abstraction here, that
     how isa has worked for ages.
s390: got rid of irq numbers already
ofw: an open firmware device can have a number of interrupts, but
     like PCI, the driver only needs to know things like 'first
     irq of this device', not how it's connected
ps3: irqs are requested from the firmware for each device, this
     can happen under the covers.
mmc, usb, phy, ieee1394: these already have a higl-level abstraction
     for interrupt events
platform: dunno, probably these really should use the struct irq
     directly
eisa, mca, pcmcia, zorro, ...: no idea, but possibly similar to PCI.

Note that we can even start converting device drivers first, before
moving away from irq numbers. A typical PCI driver should get
somewhat simpler by the conversion, and when they are all converted,
we can replace pci_dev->irq with a struct irq* under the covers.

	Arnd <><
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