[PATCH 1/4] driver core: Support two-pass driver shutdown

[Jeremy Allison]

From: Tanjore Suresh <tansuresh at google.com>

This changes the bus driver interface with an additional entry point
to enable devices to implement two-pass shutdown. The existing
synchronous interface to shutdown is called, and if a shutdown_wait
method is defined the device is moved to an alternate list.

Once the shutdown method is called for all devices, the
shutdown_wait method is then called synchronously for
all devices on the alternate list.

Signed-off-by: Tanjore Suresh <tansuresh at google.com>
Signed-off-by: Jeremy Allison <jallison at ciq.com>
---
 drivers/base/core.c        | 35 +++++++++++++++++++++++++++++++++++
 include/linux/device/bus.h |  6 +++++-
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 67ba592afc77..a66988cbaad1 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -4725,6 +4725,7 @@ EXPORT_SYMBOL_GPL(device_change_owner);
 void device_shutdown(void)
 {
 	struct device *dev, *parent;
+	LIST_HEAD(shutdown_wait_list);
 
 	wait_for_device_probe();
 	device_block_probing();
@@ -4769,10 +4770,15 @@ void device_shutdown(void)
 				dev_info(dev, "shutdown_pre\n");
 			dev->class->shutdown_pre(dev);
 		}
+
 		if (dev->bus && dev->bus->shutdown) {
 			if (initcall_debug)
 				dev_info(dev, "shutdown\n");
 			dev->bus->shutdown(dev);
+			/* Only put the device on the shutdown_wait_list
+			 * if a shutdown_wait() method is also defined. */
+			if (dev->bus->shutdown_wait)
+				list_add(&dev->kobj.entry, &shutdown_wait_list);
 		} else if (dev->driver && dev->driver->shutdown) {
 			if (initcall_debug)
 				dev_info(dev, "shutdown\n");
@@ -4789,6 +4795,35 @@ void device_shutdown(void)
 		spin_lock(&devices_kset->list_lock);
 	}
 	spin_unlock(&devices_kset->list_lock);
+
+	/*
+	 * Second pass only for devices that have configured
+	 * a shutdown_wait() method.
+	 */
+	while (!list_empty(&shutdown_wait_list)) {
+		dev = list_entry(shutdown_wait_list.next, struct device,
+				kobj.entry);
+		parent = get_device(dev->parent);
+		get_device(dev);
+		/*
+		 * Make sure the device is off the  list
+		 */
+		list_del_init(&dev->kobj.entry);
+		if (parent)
+			device_lock(parent);
+		device_lock(dev);
+		if (dev->bus && dev->bus->shutdown_wait) {
+			if (initcall_debug)
+				dev_info(dev,
+				"shutdown_wait called\n");
+			dev->bus->shutdown_wait(dev);
+		}
+		device_unlock(dev);
+		if (parent)
+			device_unlock(parent);
+		put_device(dev);
+		put_device(parent);
+	}
 }
 
 /*
diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
index ae10c4322754..6f192221b551 100644
--- a/include/linux/device/bus.h
+++ b/include/linux/device/bus.h
@@ -48,7 +48,10 @@ struct fwnode_handle;
  *		will never get called until they do.
  * @remove:	Called when a device removed from this bus.
  * @shutdown:	Called at shut-down time to quiesce the device.
- *
+ * @shutdown_wait:	If this method exists, devices are stored on a separate
+ * 			list after shutdown() has been called and
+ * 			shutdown_wait() is called synchronously on each device
+ * 			in this list in turn.
  * @online:	Called to put the device back online (after offlining it).
  * @offline:	Called to put the device offline for hot-removal. May fail.
  *
@@ -90,6 +93,7 @@ struct bus_type {
 	void (*sync_state)(struct device *dev);
 	void (*remove)(struct device *dev);
 	void (*shutdown)(struct device *dev);
+	void (*shutdown_wait)(struct device *dev);
 
 	int (*online)(struct device *dev);
 	int (*offline)(struct device *dev);
-- 
2.39.3