This patch sets hub device's default autosuspend delay as 0 to
speedup bus suspend, see comments in code for details.
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 382dc41..db17d24 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -1625,6 +1625,40 @@ 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:
+ *
+ * - The remote wakeup from child device and new connected
+ * device doesn't mean that there might be another new device
+ * which is going to be connected or disconnected to the hub,
+ * or there might be another wakeup from other devices, in
+ * the following seconds.
+ *
+ * - The wakeup event can be handled completely in hub_resume()
+ * and khubd, and the submitted status URB is just to check
+ * future changes on hub downstream ports.
+ *
+ * - the introduced hub resume delay during the autosuspend
+ * delay period doesn't matter for new device to be connected
+ * into the hub.
+ *
+ * - the child device should depend its own autosuspend delay
+ * to fit its use case and shoudn't depend on the delay of
+ * parent hub device.
+ *
+ * - suppose there is one device which will remote wakeup
+ * every 2 seconds periodically and does't care the resume
+ * delay, the bus can't be suspended with previous default
+ * autosuspend delay at all, not mention in case of several
+ * hubs connected in the path from the device to root hub.
+ *
+ * - it is safe to do so because the hub can't be auto-suspended
+ * until the remote wakeup is handled by khubd in the device
+ * remote wakeup path.
+ */
+ pm_runtime_set_autosuspend_delay(&hdev->dev, 0);
+
/* Hubs have proper suspend/resume support. */
usb_enable_autosuspend(hdev);
--
1.7.9.5
--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
