usb: fix hub-port pm_runtime_enable() vs runtime pm transitions

Commit 9262c19d14c4 "usb: disable port power control if not supported in
wHubCharacteristics" gated enabling runtime pm for usb_port devices on
whether the parent hub supports power control, which causes a
regression.  The port must still be allowed to carry out runtime pm
callbacks and receive a -EAGAIN or -EBUSY result.  Otherwise the
usb_port device will transition to the pm error state and trigger the
same for the child usb_device.

Prior to the offending commit usb_hub_create_port_device() arranged for
runtime pm to be disabled is dev_pm_qos_expose_flags() failed.  Instead,
force the default state of PM_QOS_FLAG_NO_POWER_OFF flag to be set prior
to enabling runtime pm.  If that policy can not be set then fail
registration.

Report: http://marc.info/?l=linux-usb&m=140290586301336&w=2
Fixes: 9262c19d14c4 ("usb: disable port power control if not supported in wHubCharacteristics")
Reported-by: Bjørn Mork <bjorn@mork.no>
Reported-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 54 insertions, 19 deletions

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 78c3cd20d7ae..21b99b4b4082 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -1577,6 +1577,12 @@ static int hub_configure(struct usb_hub *hub,
                 }
         }
         hdev->maxchild = i;
+        for (i = 0; i < hdev->maxchild; i++) {
+                struct usb_port *port_dev = hub->ports[i];
+
+                pm_runtime_put(&port_dev->dev);
+        }
+
         mutex_unlock(&usb_port_peer_mutex);
         if (ret < 0)
                 goto fail;
diff --git a/drivers/usb/core/hub.h b/drivers/usb/core/hub.h
index 0a7cdc0ef0a9..326308e53961 100644
--- a/drivers/usb/core/hub.h
+++ b/drivers/usb/core/hub.h
@@ -84,6 +84,7 @@ struct usb_hub {
  * @dev: generic device interface
  * @port_owner: port's owner
  * @peer: related usb2 and usb3 ports (share the same connector)
+ * @req: default pm qos request for hubs without port power control
  * @connect_type: port's connect type
  * @location: opaque representation of platform connector location
  * @status_lock: synchronize port_event() vs usb_port_{suspend|resume}
@@ -95,6 +96,7 @@ struct usb_port {
         struct device dev;
         struct usb_dev_state *port_owner;
         struct usb_port *peer;
+        struct dev_pm_qos_request *req;
         enum usb_port_connect_type connect_type;
         usb_port_location_t location;
         struct mutex status_lock;
diff --git a/drivers/usb/core/port.c b/drivers/usb/core/port.c
index 9347ade7d5fe..fe1b6d0967e3 100644
--- a/drivers/usb/core/port.c
+++ b/drivers/usb/core/port.c
@@ -68,6 +68,7 @@ static void usb_port_device_release(struct device *dev)
 {
         struct usb_port *port_dev = to_usb_port(dev);
 
+        kfree(port_dev->req);
         kfree(port_dev);
 }
 
@@ -400,9 +401,13 @@ int usb_hub_create_port_device(struct usb_hub *hub, int port1)
         int retval;
 
         port_dev = kzalloc(sizeof(*port_dev), GFP_KERNEL);
-        if (!port_dev) {
-                retval = -ENOMEM;
-                goto exit;
+        if (!port_dev)
+                return -ENOMEM;
+
+        port_dev->req = kzalloc(sizeof(*(port_dev->req)), GFP_KERNEL);
+        if (!port_dev->req) {
+                kfree(port_dev);
+                return -ENOMEM;
         }
 
         hub->ports[port1 - 1] = port_dev;
@@ -418,31 +423,53 @@ int usb_hub_create_port_device(struct usb_hub *hub, int port1)
                         port1);
         mutex_init(&port_dev->status_lock);
         retval = device_register(&port_dev->dev);
-        if (retval)
-                goto error_register;
+        if (retval) {
+                put_device(&port_dev->dev);
+                return retval;
+        }
+
+        /* Set default policy of port-poweroff disabled. */
+        retval = dev_pm_qos_add_request(&port_dev->dev, port_dev->req,
+                        DEV_PM_QOS_FLAGS, PM_QOS_FLAG_NO_POWER_OFF);
+        if (retval < 0) {
+                device_unregister(&port_dev->dev);
+                return retval;
+        }
 
         find_and_link_peer(hub, port1);
 
+        /*
+         * Enable runtime pm and hold a refernce that hub_configure()
+         * will drop once the PM_QOS_NO_POWER_OFF flag state has been set
+         * and the hub has been fully registered (hdev->maxchild set).
+         */
         pm_runtime_set_active(&port_dev->dev);
+        pm_runtime_get_noresume(&port_dev->dev);
+        pm_runtime_enable(&port_dev->dev);
+        device_enable_async_suspend(&port_dev->dev);
 
         /*
-         * Do not enable port runtime pm if the hub does not support
-         * power switching.  Also, userspace must have final say of
-         * whether a port is permitted to power-off.  Do not enable
-         * runtime pm if we fail to expose pm_qos_no_power_off.
+         * Keep hidden the ability to enable port-poweroff if the hub
+         * does not support power switching.
          */
-        if (hub_is_port_power_switchable(hub)
-                        && dev_pm_qos_expose_flags(&port_dev->dev,
-                        PM_QOS_FLAG_NO_POWER_OFF) == 0)
-                pm_runtime_enable(&port_dev->dev);
+        if (!hub_is_port_power_switchable(hub))
+                return 0;
 
-        device_enable_async_suspend(&port_dev->dev);
-        return 0;
+        /* Attempt to let userspace take over the policy. */
+        retval = dev_pm_qos_expose_flags(&port_dev->dev,
+                        PM_QOS_FLAG_NO_POWER_OFF);
+        if (retval < 0) {
+                dev_warn(&port_dev->dev, "failed to expose pm_qos_no_poweroff\n");
+                return 0;
+        }
 
-error_register:
-        put_device(&port_dev->dev);
-exit:
-        return retval;
+        /* Userspace owns the policy, drop the kernel 'no_poweroff' request. */
+        retval = dev_pm_qos_remove_request(port_dev->req);
+        if (retval >= 0) {
+                kfree(port_dev->req);
+                port_dev->req = NULL;
+        }
+        return 0;
 }
 
 void usb_hub_remove_port_device(struct usb_hub *hub, int port1)