PCI: Skip attaching driver in device_add()

We want to add PCI devices to the device tree as early as possible but
delay attaching drivers.

device_add() adds a device to the device hierarchy and (via
device_attach()) attaches a matching driver and calls its .probe() method.
We want to separate adding the device to the hierarchy from attaching the
driver.

This patch does that by adding "match_driver" in struct pci_dev.  When
false, we return failure from pci_bus_match(), which makes device_attach()
believe there's no matching driver.

Later, we set "match_driver = true" and call device_attach() again, which
now attaches the driver and calls its .probe() method.

[bhelgaas: changelog, explicitly init dev->match_driver,
fold device_attach() call into pci_bus_add_device()]
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/pci/bus.c

@@ -177,10 +177,15 @@ int pci_bus_add_device(struct pci_dev *dev)
 	if (retval)
 		return retval;
 
+	dev->match_driver = false;
 	retval = device_add(&dev->dev);
 	if (retval)
 		return retval;
 
+	dev->match_driver = true;
+	retval = device_attach(&dev->dev);
+	WARN_ON(retval < 0);
+
 	dev->is_added = 1;
 	pci_proc_attach_device(dev);
 	pci_create_sysfs_dev_files(dev);

drivers/pci/pci-driver.c

@@ -1186,9 +1186,13 @@ pci_dev_driver(const struct pci_dev *dev)
 static int pci_bus_match(struct device *dev, struct device_driver *drv)
 {
 	struct pci_dev *pci_dev = to_pci_dev(dev);
-	struct pci_driver *pci_drv = to_pci_driver(drv);
+	struct pci_driver *pci_drv;
 	const struct pci_device_id *found_id;
 
+	if (!pci_dev->match_driver)
+		return 0;
+
+	pci_drv = to_pci_driver(drv);
 	found_id = pci_match_device(pci_drv, pci_dev);
 	if (found_id)
 		return 1;

include/linux/pci.h

@@ -286,6 +286,7 @@ struct pci_dev {
 	unsigned int	irq;
 	struct resource resource[DEVICE_COUNT_RESOURCE]; /* I/O and memory regions + expansion ROMs */
 
+	bool match_driver;		/* Skip attaching driver */
 	/* These fields are used by common fixups */
 	unsigned int	transparent:1;	/* Transparent PCI bridge */
 	unsigned int	multifunction:1;/* Part of multi-function device */