This patch sets hub device's default autosuspend delay as 0 to
speedup bus suspend, see comments in code for details.
Cc: Alan Stern <st...@rowland.harvard.edu>
Signed-off-by: Ming Lei <ming....@canonical.com>
---
drivers/usb/core/hub.c | 34 ++++++++++++++++++++++++++++++++++
1 file changed, 34 insertions(+)
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index e67994c..7c2cba9 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -1629,6 +1629,40 @@ 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
+ *
+ * These quite rare devices still can 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);
--
1.7.9.5
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