[RFC PATCH v5 3/8] PCI: add a blocking notifier chain for PCI bus addition/removal

[Jiang Liu <liuj97@gmail.com>]

When adding/removing a PCI bus, some other components want to be
notified so they could update their states. For example, the pci_slot
driver needs to create/destroy PCI slots attaching to the PCI bus.
So introduce a dedicate blocking notifier chain for PCI bus
addition/removal events. It could be extended to support PCI device
addition/removal events in the future when needed.

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
---
 drivers/pci/bus.c    |   24 ++++++++++++++++++++++++
 drivers/pci/pci.h    |    1 +
 drivers/pci/probe.c  |    2 ++
 drivers/pci/remove.c |    1 +
 include/linux/pci.h  |   12 ++++++++++++
 5 files changed, 40 insertions(+)

diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
index 4c843cd..8bbd3f2 100644
--- a/drivers/pci/bus.c
+++ b/drivers/pci/bus.c
@@ -13,11 +13,33 @@
 #include <linux/errno.h>
 #include <linux/ioport.h>
 #include <linux/proc_fs.h>
+#include <linux/notifier.h>
 #include <linux/init.h>
 #include <linux/slab.h>
 
 #include "pci.h"
 
+static BLOCKING_NOTIFIER_HEAD(pci_bus_notifier_chain);
+
+int pci_bus_register_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&pci_bus_notifier_chain, nb);
+}
+
+int pci_bus_unregister_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&pci_bus_notifier_chain, nb);
+}
+
+void pci_bus_call_notifier(struct pci_bus *bus, unsigned long code)
+{
+	int ret;
+
+	ret = blocking_notifier_call_chain(&pci_bus_notifier_chain,
+					   code, bus);
+	WARN_ON(ret != NOTIFY_DONE && ret != NOTIFY_OK);
+}
+
 void pci_add_resource_offset(struct list_head *resources, struct resource *res,
 			     resource_size_t offset)
 {
@@ -197,6 +219,8 @@ int pci_bus_add_child(struct pci_bus *bus)
 	if (retval)
 		return retval;
 
+	pci_bus_call_notifier(bus, PCI_NOTIFY_POST_BUS_ADD);
+
 	bus->is_added = 1;
 
 	/* Create legacy_io and legacy_mem files for this bus */
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 7414094..988e4b4 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -208,6 +208,7 @@ extern int __pci_read_base(struct pci_dev *dev, enum pci_bar_type type,
 extern int pci_resource_bar(struct pci_dev *dev, int resno,
 			    enum pci_bar_type *type);
 extern int pci_bus_add_child(struct pci_bus *bus);
+extern void pci_bus_call_notifier(struct pci_bus *bus, unsigned long code);
 extern void pci_enable_ari(struct pci_dev *dev);
 /**
  * pci_ari_enabled - query ARI forwarding status
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index adb77c6..7db6528 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1679,6 +1679,8 @@ struct pci_bus *pci_create_root_bus(struct device *parent, int bus,
 	if (error)
 		goto class_dev_reg_err;
 
+	pci_bus_call_notifier(b, PCI_NOTIFY_POST_BUS_ADD);
+
 	/* Create legacy_io and legacy_mem files for this bus */
 	pci_create_legacy_files(b);
 
diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c
index 0d03026..2d8fbc8 100644
--- a/drivers/pci/remove.c
+++ b/drivers/pci/remove.c
@@ -50,6 +50,7 @@ void pci_remove_bus(struct pci_bus *bus)
 	up_write(&pci_bus_sem);
 	if (bus->is_added) {
 		pci_remove_legacy_files(bus);
+		pci_bus_call_notifier(bus, PCI_NOTIFY_PRE_BUS_DEL);
 		device_del(&bus->dev);
 	}
 	put_device(&bus->dev);
diff --git a/include/linux/pci.h b/include/linux/pci.h
index ee21795..12e5447 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1033,6 +1033,18 @@ const struct pci_device_id *pci_match_id(const struct pci_device_id *ids,
 int pci_scan_bridge(struct pci_bus *bus, struct pci_dev *dev, int max,
 		    int pass);
 
+/*
+ * All notifiers below get called with the target struct pci_bus *bus as
+ * an argument.
+ * Note: all PCI bus notifier must return success. Currently there's no
+ * error handling if any notifier returns error code.
+ */
+#define	PCI_NOTIFY_POST_BUS_ADD		0x00000001 /* PCI bus has been added */
+#define	PCI_NOTIFY_PRE_BUS_DEL		0x00000002 /* PCI bus will be deleted */
+
+int pci_bus_register_notifier(struct notifier_block *nb);
+int pci_bus_unregister_notifier(struct notifier_block *nb);
+
 void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
 		  void *userdata);
 int pci_cfg_space_size_ext(struct pci_dev *dev);
-- 
1.7.9.5