linux-kernel - Re: [git patch] free

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Message-ID: <4810C3B5.3020605@garzik.org>
Date:	Thu, 24 Apr 2008 13:30:29 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rene Herman <rene.herman@...access.nl>,
	Adrian Bunk <bunk@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, rmk@....linux.org.uk,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [git patch] free_irq() fixes

Eric W. Biederman wrote:
> Even if we never export them to drivers we will need to implement
> in genirq functions like:
> 
> int __must_check irq_request(struct irq_desc *irq, irq_handler_t handler,
> 	 unsigned long irqflags, const char *devname, void *devid);
>         	
> int __must_check request_irq(unsigned int irq, irq_handler_t handler,
> 	unsigned long irqflags, const char *devname, void *devid)
> {
>         return irq_request(cookie_to_desc(irq), handler, irqflags, devname, devid);
> }
> 
> Or at the very least do the mapping from cookie to irq_desc at the
> start of all of the genirq functions.  One valid implementation of
> that cookie to desc will be the current array lookup.  But for x86
> we need something less limiting.
[...]
> And on x86 at least the hardware maps the MSI write into an interrupt.
> So there is not an opportunity to get any metdata/OOB data from the
> MSI message.  Instead we just potentially get a boatload more irq
> sources.  Which is one of the things making a static NR_IRQS painful.
> 
> To be safe we have to make NR_IRQS 10x+ or so bigger then people use
> today.  Just in case they decide to plug in some really irq hungry
> cards.


Just to be clear, irq_chip/irq_desc and metadata/OOB data are two very 
different beasts.  irq_chip/irq_desc is more a system attribute as Linus 
notes.  Also, it doesn't change very often.

metadata/OOB, on the other hand, is different -for each interrupt-, and 
is highly relevant to drivers.  Thus should be part of the driver API 
somehow.

	Jeff


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