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authorMing Lei <ming.lei@canonical.com>2012-10-24 11:59:25 +0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-10-25 11:45:32 -0700
commit596d789a211d134dc5f94d1e5957248c204ef850 (patch)
tree6ffb0552cde7a5d607119251a337d66c583a9362
parente6f30deafe61179df048ac9040fe2bdf73a996c3 (diff)
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>
-rw-r--r--drivers/usb/core/hub.c35
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);