1 files changed, 137 insertions, 1 deletions

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 142e3d600f14..442b7641a086 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -28,6 +28,133 @@
 #include "base.h"
 #include "power/power.h"
 
+/*
+ * Deferred Probe infrastructure.
+ *
+ * Sometimes driver probe order matters, but the kernel doesn't always have
+ * dependency information which means some drivers will get probed before a
+ * resource it depends on is available.  For example, an SDHCI driver may
+ * first need a GPIO line from an i2c GPIO controller before it can be
+ * initialized.  If a required resource is not available yet, a driver can
+ * request probing to be deferred by returning -EPROBE_DEFER from its probe hook
+ *
+ * Deferred probe maintains two lists of devices, a pending list and an active
+ * list.  A driver returning -EPROBE_DEFER causes the device to be added to the
+ * pending list.  A successful driver probe will trigger moving all devices
+ * from the pending to the active list so that the workqueue will eventually
+ * retry them.
+ *
+ * The deferred_probe_mutex must be held any time the deferred_probe_*_list
+ * of the (struct device*)->deferred_probe pointers are manipulated
+ */
+static DEFINE_MUTEX(deferred_probe_mutex);
+static LIST_HEAD(deferred_probe_pending_list);
+static LIST_HEAD(deferred_probe_active_list);
+static struct workqueue_struct *deferred_wq;
+
+/**
+ * deferred_probe_work_func() - Retry probing devices in the active list.
+ */
+static void deferred_probe_work_func(struct work_struct *work)
+{
+	struct device *dev;
+	/*
+	 * This block processes every device in the deferred 'active' list.
+	 * Each device is removed from the active list and passed to
+	 * bus_probe_device() to re-attempt the probe.  The loop continues
+	 * until every device in the active list is removed and retried.
+	 *
+	 * Note: Once the device is removed from the list and the mutex is
+	 * released, it is possible for the device get freed by another thread
+	 * and cause a illegal pointer dereference.  This code uses
+	 * get/put_device() to ensure the device structure cannot disappear
+	 * from under our feet.
+	 */
+	mutex_lock(&deferred_probe_mutex);
+	while (!list_empty(&deferred_probe_active_list)) {
+		dev = list_first_entry(&deferred_probe_active_list,
+					typeof(*dev), deferred_probe);
+		list_del_init(&dev->deferred_probe);
+
+		get_device(dev);
+
+		/* Drop the mutex while probing each device; the probe path
+		 * may manipulate the deferred list */
+		mutex_unlock(&deferred_probe_mutex);
+		dev_dbg(dev, "Retrying from deferred list\n");
+		bus_probe_device(dev);
+		mutex_lock(&deferred_probe_mutex);
+
+		put_device(dev);
+	}
+	mutex_unlock(&deferred_probe_mutex);
+}
+static DECLARE_WORK(deferred_probe_work, deferred_probe_work_func);
+
+static void driver_deferred_probe_add(struct device *dev)
+{
+	mutex_lock(&deferred_probe_mutex);
+	if (list_empty(&dev->deferred_probe)) {
+		dev_dbg(dev, "Added to deferred list\n");
+		list_add(&dev->deferred_probe, &deferred_probe_pending_list);
+	}
+	mutex_unlock(&deferred_probe_mutex);
+}
+
+void driver_deferred_probe_del(struct device *dev)
+{
+	mutex_lock(&deferred_probe_mutex);
+	if (!list_empty(&dev->deferred_probe)) {
+		dev_dbg(dev, "Removed from deferred list\n");
+		list_del_init(&dev->deferred_probe);
+	}
+	mutex_unlock(&deferred_probe_mutex);
+}
+
+static bool driver_deferred_probe_enable = false;
+/**
+ * driver_deferred_probe_trigger() - Kick off re-probing deferred devices
+ *
+ * This functions moves all devices from the pending list to the active
+ * list and schedules the deferred probe workqueue to process them.  It
+ * should be called anytime a driver is successfully bound to a device.
+ */
+static void driver_deferred_probe_trigger(void)
+{
+	if (!driver_deferred_probe_enable)
+		return;
+
+	/* A successful probe means that all the devices in the pending list
+	 * should be triggered to be reprobed.  Move all the deferred devices
+	 * into the active list so they can be retried by the workqueue */
+	mutex_lock(&deferred_probe_mutex);
+	list_splice_tail_init(&deferred_probe_pending_list,
+			      &deferred_probe_active_list);
+	mutex_unlock(&deferred_probe_mutex);
+
+	/* Kick the re-probe thread.  It may already be scheduled, but
+	 * it is safe to kick it again. */
+	queue_work(deferred_wq, &deferred_probe_work);
+}
+
+/**
+ * deferred_probe_initcall() - Enable probing of deferred devices
+ *
+ * We don't want to get in the way when the bulk of drivers are getting probed.
+ * Instead, this initcall makes sure that deferred probing is delayed until
+ * late_initcall time.
+ */
+static int deferred_probe_initcall(void)
+{
+	deferred_wq = create_singlethread_workqueue("deferwq");
+	if (WARN_ON(!deferred_wq))
+		return -ENOMEM;
+
+	driver_deferred_probe_enable = true;
+	driver_deferred_probe_trigger();
+	return 0;
+}
+late_initcall(deferred_probe_initcall);
 
 static void driver_bound(struct device *dev)
 {
@@ -42,6 +169,11 @@ static void driver_bound(struct device *dev)
 
 	klist_add_tail(&dev->p->knode_driver, &dev->driver->p->klist_devices);
 
+	/* Make sure the device is no longer in one of the deferred lists
+	 * and kick off retrying all pending devices */
+	driver_deferred_probe_del(dev);
+	driver_deferred_probe_trigger();
+
 	if (dev->bus)
 		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
 					     BUS_NOTIFY_BOUND_DRIVER, dev);
@@ -142,7 +274,11 @@ probe_failed:
 	driver_sysfs_remove(dev);
 	dev->driver = NULL;
 
-	if (ret != -ENODEV && ret != -ENXIO) {
+	if (ret == -EPROBE_DEFER) {
+		/* Driver requested deferred probing */
+		dev_info(dev, "Driver %s requests probe deferral\n", drv->name);
+		driver_deferred_probe_add(dev);
+	} else if (ret != -ENODEV && ret != -ENXIO) {
 		/* driver matched but the probe failed */
 		printk(KERN_WARNING
 		       "%s: probe of %s failed with error %d\n",