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>
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index ff86355..43ce146 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -1614,6 +1614,41 @@
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);