Re: [PATCH] PCI: Add pci shutdown ability

[Alan Stern <stern@rowland.harvard.edu>]

On Tue, 26 Apr 2005, Grant Grundler wrote:

> > I looked into the possibility of having the PCI core disable interrupt
> > generation and DMA on each new device as it is discovered.  Unfortunately
> > there is no dependable, universal way to do this for IRQs.
> 
> Sure there is. Every IRQ line goes to an IRQ controller.
> Arch specific code deals with programming the controller and can
> mask all interrupts (or not). Historically, they've been left unmasked
> for ISA IRQ discovery and debugging misrouted IRQ lines.

This doesn't help.  Consider what happens when two devices share an IRQ
line.  Suppose device B is generating interrupt requests when the driver
for device A is probed.  The driver registers its handler, which causes
the IRQ line to be unmasked.  Then a multitude of IRQs arrive from B, none
of which can be handled by A's driver.  So the kernel shuts the IRQ line
down permanently...

Alan Stern

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