linux-kernel - Re: [PATCH/RFC] PCI prepare/activate instead of enable to avoid IRQ storm and rogue DMA access

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Date:	Wed, 14 Mar 2007 22:58:18 +0000
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Tejun Heo <htejun@...il.com>, gregkh@...e.de,
	linux-kernel@...r.kernel.org, linux-pci@...ey.karlin.mff.cuni.cz,
	michal.k.k.piotrowski@...il.com, linux-ide@...r.kernel.org,
	tglx@...utronix.de, shemminger@...ux-foundation.org,
	mlord@...ox.com, linux-pm@...ts.osdl.org
Subject: Re: [PATCH/RFC] PCI prepare/activate instead of enable to avoid IRQ storm and rogue DMA access

On Wed, Mar 14, 2007 at 06:34:11PM -0400, Jeff Garzik wrote:
> Russell King wrote:
> >pci_enable_device() doesn't deal with this; in most PCI setups I've
> >seen, there is no control at PCI level over whether a device generates
> >an interrupt on the bus.  Certainly the memory and io command enables
> 
> PCI grew an interrupt enable while you weren't looking: 
> PCI_COMMAND_INTX_DISABLE

That's fine for devices which conform to the later PCI specs, but not
all do.

> It was added in PCI 2.3 I think.

Correct.

> Older PCI devices certainly do not have this standardized bit.

No PCI device that I have has that bit - including the raid card I
bought last year...

In any case, relying on such a new control bit to implement this kind
of functionality would result in a very hit and miss result; Linux
tends to get used on things other than the bleeding edge of hardware
technology.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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