[RFC PATCH 7/8] pci: Add slot and bus reset interfaces

[Alex Williamson <alex.williamson@redhat.com>]

Sometimes pci_reset_function is not sufficient.  We have cases where
devices do not support any kind of reset, but there might be multiple
functions on the bus, preventing pci_reset_function from doing a
secondary bus reset.  We also have cases where a device will advertise
that it supports a PM reset, but really does nothing on D3hot->D0
(graphics cards are notorious for this).  These devices often also
have more than one function, so even blacklisting PM reset for them
wouldn't allow a secondary bus reset through pci_reset_function.

If a driver supports multiple devices it should have the ability to
induce a bus reset when it needs to.  This patch provides that ability
through pci_reset_slot and pci_reset_bus.  It's the caller's
responsibility when using these interfaces to understand that all of
the devices in or below the slot (or on or below the bus) will be
reset and therefore should be under control of the caller.  PCI state
of all the affected devices is saved and restored around these resets,
but internal state of all of the affected devices is reset (which
should be the intention).

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---
 drivers/pci/pci.c   |  199 +++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/pci.h |    2 +
 2 files changed, 201 insertions(+)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index a330ebb..6d17807 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3432,6 +3432,205 @@ int pci_reset_function(struct pci_dev *dev)
 }
 EXPORT_SYMBOL_GPL(pci_reset_function);
 
+static void pci_bus_lock(struct pci_bus *bus)
+{
+	struct pci_dev *dev;
+
+	list_for_each_entry(dev, &bus->devices, bus_list) {
+		pci_dev_lock(dev);
+		if (dev->subordinate)
+			pci_bus_lock(dev->subordinate);
+	}
+}
+
+static void pci_bus_unlock(struct pci_bus *bus)
+{
+	struct pci_dev *dev;
+
+	list_for_each_entry(dev, &bus->devices, bus_list) {
+		pci_dev_unlock(dev);
+		if (dev->subordinate)
+			pci_bus_unlock(dev->subordinate);
+	}
+}
+
+static void pci_slot_lock(struct pci_slot *slot)
+{
+	struct pci_dev *dev;
+
+	BUG_ON(!slot);
+
+	list_for_each_entry(dev, &slot->bus->devices, bus_list) {
+		if (dev->slot && dev->slot == slot)
+			pci_dev_lock(dev);
+		if (dev->subordinate)
+			pci_bus_lock(dev->subordinate);
+	}
+}
+
+static void pci_slot_unlock(struct pci_slot *slot)
+{
+	struct pci_dev *dev;
+
+	BUG_ON(!slot);
+
+	list_for_each_entry(dev, &slot->bus->devices, bus_list) {
+		if (dev->slot && dev->slot == slot)
+			pci_dev_unlock(dev);
+		if (dev->subordinate)
+			pci_bus_unlock(dev->subordinate);
+	}
+}
+
+static void pci_bus_save(struct pci_bus *bus)
+{
+	struct pci_dev *dev;
+
+	list_for_each_entry(dev, &bus->devices, bus_list) {
+		pci_dev_save(dev);
+		if (dev->subordinate)
+			pci_bus_lock(dev->subordinate);
+	}
+}
+
+static void pci_bus_restore(struct pci_bus *bus)
+{
+	struct pci_dev *dev;
+
+	list_for_each_entry(dev, &bus->devices, bus_list) {
+		pci_dev_restore(dev);
+		if (dev->subordinate)
+			pci_bus_unlock(dev->subordinate);
+	}
+}
+
+static void pci_slot_save(struct pci_slot *slot)
+{
+	struct pci_dev *dev;
+
+	BUG_ON(!slot);
+
+	list_for_each_entry(dev, &slot->bus->devices, bus_list) {
+		if (dev->slot && dev->slot == slot)
+			pci_dev_save(dev);
+		if (dev->subordinate)
+			pci_bus_save(dev->subordinate);
+	}
+}
+
+static void pci_slot_restore(struct pci_slot *slot)
+{
+	struct pci_dev *dev;
+
+	BUG_ON(!slot);
+
+	list_for_each_entry(dev, &slot->bus->devices, bus_list) {
+		if (dev->slot && dev->slot == slot)
+			pci_dev_restore(dev);
+		if (dev->subordinate)
+			pci_bus_restore(dev->subordinate);
+	}
+}
+
+static int pci_slot_reset(struct pci_slot *slot, int probe)
+{
+	int rc;
+
+	if (!slot)
+		return -ENOTTY;
+
+	if (!probe)
+		pci_slot_lock(slot);
+
+	might_sleep();
+
+	rc = pci_hp_reset_slot(slot->hotplug, probe);
+
+	if (!probe)
+		pci_slot_unlock(slot);
+
+	return rc;
+}
+
+/**
+ * pci_reset_slot - reset a PCI slot
+ * @slot: PCI slot to reset
+ *
+ * A PCI bus may host multiple slots, each slot may support a reset mechanism
+ * independent of other slots.  For instance, some slots may support slot power
+ * control.  In the case of a 1:1 bus to slot architecture, this function may
+ * wrap the bus reset to avoid spurious slot related events, such as hotplug.
+ * Generally a slot reset should be attempted before a bus reset.  All of the
+ * function of the slot and any subordinate buses behind the slot are reset
+ * through this function.  PCI config space of all devices in the slot and
+ * behind the slot is saved before and restored after reset.
+ *
+ * Return 0 on success, non-zero on error.
+ */
+int pci_reset_slot(struct pci_slot *slot)
+{
+	int rc;
+
+	rc = pci_slot_reset(slot, 1);
+	if (rc)
+		return rc;
+
+	pci_slot_save(slot);
+
+	rc = pci_slot_reset(slot, 0);
+
+	pci_slot_restore(slot);
+
+	return rc;
+}
+EXPORT_SYMBOL_GPL(pci_reset_slot);
+
+static int pci_bus_reset(struct pci_bus *bus, int probe)
+{
+	if (!bus->self)
+		return -ENOTTY;
+
+	if (probe)
+		return 0;
+
+	pci_bus_lock(bus);
+
+	might_sleep();
+
+	pci_reset_bridge_secondary_bus(bus->self);
+
+	pci_bus_unlock(bus);
+
+	return 0;
+}
+
+/**
+ * pci_reset_bus - reset a PCI bus
+ * @bus: top level PCI bus to reset
+ *
+ * Do a bus reset on the given bus and any subordinate buses, saving
+ * and restoring state of all devices.
+ *
+ * Return 0 on success, non-zero on error.
+ */
+int pci_reset_bus(struct pci_bus *bus)
+{
+	int rc;
+
+	rc = pci_bus_reset(bus, 1);
+	if (rc)
+		return rc;
+
+	pci_bus_save(bus);
+
+	rc = pci_bus_reset(bus, 0);
+
+	pci_bus_restore(bus);
+
+	return rc;
+}
+EXPORT_SYMBOL_GPL(pci_reset_bus);
+
 /**
  * pcix_get_max_mmrbc - get PCI-X maximum designed memory read byte count
  * @dev: PCI device to query
diff --git a/include/linux/pci.h b/include/linux/pci.h
index fc85d68..cf4cf10 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -922,6 +922,8 @@ int pcie_set_mps(struct pci_dev *dev, int mps);
 int __pci_reset_function(struct pci_dev *dev);
 int __pci_reset_function_locked(struct pci_dev *dev);
 int pci_reset_function(struct pci_dev *dev);
+int pci_reset_slot(struct pci_slot *slot);
+int pci_reset_bus(struct pci_bus *bus);
 void pci_reset_bridge_secondary_bus(struct pci_dev *dev);
 void pci_update_resource(struct pci_dev *dev, int resno);
 int __must_check pci_assign_resource(struct pci_dev *dev, int i);