PCI: Introduce /sys/bus/pci/rescan

This interface allows the user to force a rescan of all PCI buses
in system, and rediscover devices that have been removed earlier.

pci_bus_attrs implementation from Trent Piepho.

Thanks to Vegard Nossum for discovering locking issues with the
sysfs interface.

Cc: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

Documentation/ABI/testing/sysfs-bus-pci

@@ -57,6 +57,15 @@ Description:
 		match the driver to the device.  For example:
 		# echo "8086 10f5" > /sys/bus/pci/drivers/foo/remove_id
 
+What:		/sys/bus/pci/rescan
+Date:		January 2009
+Contact:	Linux PCI developers <linux-pci@vger.kernel.org>
+Description:
+		Writing a non-zero value to this attribute will
+		force a rescan of all PCI buses in the system, and
+		re-discover previously removed devices.
+		Depends on CONFIG_HOTPLUG.
+
 What:		/sys/bus/pci/devices/.../vpd
 Date:		February 2008
 Contact:	Ben Hutchings <bhutchings@solarflare.com>

drivers/pci/pci-driver.c

@@ -1049,6 +1049,7 @@ struct bus_type pci_bus_type = {
 	.remove		= pci_device_remove,
 	.shutdown	= pci_device_shutdown,
 	.dev_attrs	= pci_dev_attrs,
+	.bus_attrs	= pci_bus_attrs,
 	.pm		= PCI_PM_OPS_PTR,
 };
 

drivers/pci/pci-sysfs.c

@@ -219,6 +219,32 @@ msi_bus_store(struct device *dev, struct device_attribute *attr,
 	return count;
 }
 
+#ifdef CONFIG_HOTPLUG
+static DEFINE_MUTEX(pci_remove_rescan_mutex);
+static ssize_t bus_rescan_store(struct bus_type *bus, const char *buf,
+				size_t count)
+{
+	unsigned long val;
+	struct pci_bus *b = NULL;
+
+	if (strict_strtoul(buf, 0, &val) < 0)
+		return -EINVAL;
+
+	if (val) {
+		mutex_lock(&pci_remove_rescan_mutex);
+		while ((b = pci_find_next_bus(b)) != NULL)
+			pci_rescan_bus(b);
+		mutex_unlock(&pci_remove_rescan_mutex);
+	}
+	return count;
+}
+
+struct bus_attribute pci_bus_attrs[] = {
+	__ATTR(rescan, (S_IWUSR|S_IWGRP), NULL, bus_rescan_store),
+	__ATTR_NULL
+};
+#endif
+
 struct device_attribute pci_dev_attrs[] = {
 	__ATTR_RO(resource),
 	__ATTR_RO(vendor),

drivers/pci/pci.h

@@ -138,6 +138,12 @@ extern int pcie_mch_quirk;
 extern struct device_attribute pci_dev_attrs[];
 extern struct device_attribute dev_attr_cpuaffinity;
 extern struct device_attribute dev_attr_cpulistaffinity;
+#ifdef CONFIG_HOTPLUG
+extern struct bus_attribute pci_bus_attrs[];
+#else
+#define pci_bus_attrs	NULL
+#endif
+
 
 /**
  * pci_match_one_device - Tell if a PCI device structure has a matching

drivers/pci/probe.c

@@ -1228,13 +1228,13 @@ unsigned int __devinit pci_rescan_bus(struct pci_bus *bus)
 
 	max = pci_scan_child_bus(bus);
 
-	up_read(&pci_bus_sem);
+	down_read(&pci_bus_sem);
 	list_for_each_entry(dev, &bus->devices, bus_list)
 		if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE ||
 		    dev->hdr_type == PCI_HEADER_TYPE_CARDBUS)
 			if (dev->subordinate)
 				pci_bus_size_bridges(dev->subordinate);
-	down_read(&pci_bus_sem);
+	up_read(&pci_bus_sem);
 
 	pci_bus_assign_resources(bus);
 	pci_enable_bridges(bus);