amd64-agp conflicts with sis-agp

[Ben Hutchings <ben@decadent.org.uk>]

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This code in agp_amd64_init() can optionally bind to devices
generically, and it does this without going through the device core:

		/* Look for any AGP bridge */
		dev = NULL;
		err = -ENODEV;
		for_each_pci_dev(dev) {
			if (!pci_find_capability(dev, PCI_CAP_ID_AGP))
				continue;
			/* Only one bridge supported right now */
			if (agp_amd64_probe(dev, NULL) == 0) {
				err = 0;
				break;
			}
		}

This is causing crashes on some systems where sis-agp is already bound
to the device.  It could even race with binding of another driver when
they are both built-in.  I think it should be using something like the
following instead of directly calling agp_amd64_probe():

			down(&dev->dev.sem);
			if (!dev->dev.driver &&
			    driver_probe_device(&drv->driver, &dev->dev) == 0)
				err = 0;
			up(&dev->dev.sem);
			if (err == 0)
				break;

Ben.

-- 
Ben Hutchings
Power corrupts.  Absolute power is kind of neat.
                           - John Lehman, Secretary of the US Navy 1981-1987

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