driver-core: add asynchronous probing support for drivers

Some devices take a long time when initializing, and not all drivers are
suited to initialize their devices when they are open. For example,
input drivers need to interrogate their devices in order to publish
device's capabilities before userspace will open them. When such drivers
are compiled into kernel they may stall entire kernel initialization.

This change allows drivers request for their probe functions to be
called asynchronously during driver and device registration (manual
binding is still synchronous). Because async_schedule is used to perform
asynchronous calls module loading will still wait for the probing to
complete.

Note that the end goal is to make the probing asynchronous by default,
so annotating drivers with PROBE_PREFER_ASYNCHRONOUS is a temporary
measure that allows us to speed up boot process while we validating and
fixing the rest of the drivers and preparing userspace.

This change is based on earlier patch by "Luis R. Rodriguez"
<mcgrof@suse.com>

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 23 insertions, 8 deletions

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index 79bc203f51ef..500592486e88 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -10,6 +10,7 @@
  *
  */
 
+#include <linux/async.h>
 #include <linux/device.h>
 #include <linux/module.h>
 #include <linux/errno.h>
@@ -549,15 +550,12 @@ void bus_probe_device(struct device *dev)
 {
         struct bus_type *bus = dev->bus;
         struct subsys_interface *sif;
-        int ret;
 
         if (!bus)
                 return;
 
-        if (bus->p->drivers_autoprobe) {
-                ret = device_attach(dev);
-                WARN_ON(ret < 0);
-        }
+        if (bus->p->drivers_autoprobe)
+                device_initial_probe(dev);
 
         mutex_lock(&bus->p->mutex);
         list_for_each_entry(sif, &bus->p->interfaces, node)
@@ -659,6 +657,17 @@ static ssize_t uevent_store(struct device_driver *drv, const char *buf,
 }
 static DRIVER_ATTR_WO(uevent);
 
+static void driver_attach_async(void *_drv, async_cookie_t cookie)
+{
+        struct device_driver *drv = _drv;
+        int ret;
+
+        ret = driver_attach(drv);
+
+        pr_debug("bus: '%s': driver %s async attach completed: %d\n",
+                 drv->bus->name, drv->name, ret);
+}
+
 /**
  * bus_add_driver - Add a driver to the bus.
  * @drv: driver.
@@ -691,9 +700,15 @@ int bus_add_driver(struct device_driver *drv)
 
         klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);
         if (drv->bus->p->drivers_autoprobe) {
-                error = driver_attach(drv);
-                if (error)
-                        goto out_unregister;
+                if (driver_allows_async_probing(drv)) {
+                        pr_debug("bus: '%s': probing driver %s asynchronously\n",
+                                drv->bus->name, drv->name);
+                        async_schedule(driver_attach_async, drv);
+                } else {
+                        error = driver_attach(drv);
+                        if (error)
+                                goto out_unregister;
+                }
         }
         module_add_driver(drv->owner, drv);