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

[Alan Stern]

On Thu, 15 Mar 2007, Tejun Heo wrote:

> Hello, all.
> 
> This patch started off from the following thread.
> 
>   http://thread.gmane.org/gmane.linux.ide/16899
> 
> The problem is that a PCI device can be in any arbitrary when it gets
> enabled and the device has to be enabled for its driver to
> initialize/reset it.  The most common case this causes headache is as
> follows.
> 
> Let's assume there's a device which shares its INTX IRQ line with
> another device and the other one is already initialized.  During boot,
> due to BIOS's fault, bad hardware design or sheer bad luck, the device
> has got a pending IRQ.  When its driver enables the device, the
> pending IRQ hits INTX.  The IRQ line has been enabled by the other
> driver sharing the IRQ but IRQ handler for this device hasn't been
> registered yet.  So, screaming interrupts.  IRQ subsystem shuts up the
> IRQ line in an attempt to save the machine from complete lockup and
> both devices end up dead.

In several cases this problem has indeed come up and been fixed by adding
a PCI quirk routine to turn off the device's pending IRQ.

Alan Stern

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