USB: set hub's default autosuspend delay as 0

This patch sets hub device's default autosuspend delay as 0 to
speedup bus suspend, see comments in code for details.

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 35 insertions, 0 deletions

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index ff86355d0dfc..43ce1467f8c0 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -1614,6 +1614,41 @@ static int hub_probe(struct usb_interface *intf, const struct usb_device_id *id)
         desc = intf->cur_altsetting;
         hdev = interface_to_usbdev(intf);
 
+        /*
+         * Set default autosuspend delay as 0 to speedup bus suspend,
+         * based on the below considerations:
+         *
+         * - Unlike other drivers, the hub driver does not rely on the
+         *   autosuspend delay to provide enough time to handle a wakeup
+         *   event, and the submitted status URB is just to check future
+         *   change on hub downstream ports, so it is safe to do it.
+         *
+         * - The patch might cause one or more auto supend/resume for
+         *   below very rare devices when they are plugged into hub
+         *   first time:
+         *
+         *      devices having trouble initializing, and disconnect
+         *      themselves from the bus and then reconnect a second
+         *      or so later
+         *
+         *      devices just for downloading firmware, and disconnects
+         *      themselves after completing it
+         *
+         *   For these quite rare devices, their drivers may change the
+         *   autosuspend delay of their parent hub in the probe() to one
+         *   appropriate value to avoid the subtle problem if someone
+         *   does care it.
+         *
+         * - The patch may cause one or more auto suspend/resume on
+         *   hub during running 'lsusb', but it is probably too
+         *   infrequent to worry about.
+         *
+         * - Change autosuspend delay of hub can avoid unnecessary auto
+         *   suspend timer for hub, also may decrease power consumption
+         *   of USB bus.
+         */
+        pm_runtime_set_autosuspend_delay(&hdev->dev, 0);
+
         /* Hubs have proper suspend/resume support. */
         usb_enable_autosuspend(hdev);