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Date: Sat, 15 Jun 2002 11:48:17 -0700 (PDT)
From: Linus Torvalds <torvalds@transmeta.com>
To: Jeff Garzik <jgarzik@mandrakesoft.com>
cc: Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de>,
        Vojtech Pavlik <vojtech@suse.cz>, Peter Osterlund <petero2@telia.com>,
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        Alessandro Suardi <alessandro.suardi@oracle.com>,
        <linux-kernel@vger.kernel.org>
Subject: Re: 2.5.20 - Xircom PCI Cardbus doesn't work
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On Fri, 14 Jun 2002, Jeff Garzik wrote:
>
> Can someone clarify for me the need of pci_request_irq??
>
> pci_enable_device() assigns the IRQ in routing, but it is not enabled
> until you call request_irq.  I don't see any simplification that can be
> done in the PCI API.

The irq _is_ enabled ona hardware level.

Which can be a total disaster if there are shared PCI irq's, and the
interrupt is "screaming" (ie an active level-sensitive thing).

We've had this on cardbus, for example, where we need to do an
"pci_emable_device()" in order to get access to the PCI IO mappings, which
are needed to shut the device up.

Right now the solution to a screaming device can be something as nasty as

	cli();
	pci_enable_device();
	disable_irq(dev->irq);
	sti();

	/* IRQ handling needs this ioremapped */
	membase = ioremap(dev->resource[]);
	request_irq(dev->irq);

	/* Now we can enable the irq, because we have a valid handler */
	enable_irq(dev->irq);

which is horribly stupid. We really want to do

	pci_enable_mem(dev);
	membase = ioremap(dev->resource[]);

	pci_request_irq(dev, irq_handler);

where "pci_request_irq()" enables the interrupt and adds an interrupt
handler atomically.

> The only thing I've wanted is a cross-platform way to detect if
> pdev->irq returned by pci_enable_device is valid.

It's required to be valid, because if it isn't, then the platform is
broken. There are no cross-platform issues: complain to the platform
vendor and/or the linux code for that architecture.

		Linus

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