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>

5 files changed, 44 insertions, 2 deletions

diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
index d175a2a5fac2..e6ad047cb3c2 100644
--- a/Documentation/ABI/testing/sysfs-bus-pci
+++ b/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>
diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 87a5ddbb324f..95d198570290 100644
--- a/drivers/pci/pci-driver.c
+++ b/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,
 };
 
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index ec7a175dcbaf..be7468a5eb72 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/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),
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 22dcfdb75d91..45833a5bca61 100644
--- a/drivers/pci/pci.h
+++ b/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
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 60a8e5fec6c5..56c71e585f3d 100644
--- a/drivers/pci/probe.c
+++ b/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);