1 files changed, 147 insertions, 1 deletions

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 142e3d600f14..1b1cbb571d38 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -28,6 +28,141 @@
 #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*)->p->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;
+        struct device_private *private;
+        /*
+         * 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)) {
+                private = list_first_entry(&deferred_probe_active_list,
+                                        typeof(*dev->p), deferred_probe);
+                dev = private->device;
+                list_del_init(&private->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->p->deferred_probe)) {
+                dev_dbg(dev, "Added to deferred list\n");
+                list_add(&dev->p->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->p->deferred_probe)) {
+                dev_dbg(dev, "Removed from deferred list\n");
+                list_del_init(&dev->p->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 +177,13 @@ 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 +284,11 @@ 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",