USB: change hub initialization sleeps to delayed_work

This patch (as1137) changes the hub_activate() routine, replacing the
power-power-up and debounce delays with delayed_work calls. The idea
is that on systems where the USB stack is compiled into the kernel
rather than built as modules, these delays will no longer block the
boot thread. At least 100 ms is saved for each root hub, which can
add up to a significant savings in total boot time.

Arjan van de Ven was very pleased to see that this shaved 700 ms off
his computer's boot time. Since his total boot time is on the order
of two seconds, the improvement is considerable.

Signed-off-by: Alan Stern <[e-mail]>
Tested-by: Arjan van de Ven <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/core/hub.c

···
 	unsigned		has_indicators:1;
 	u8			indicator[USB_MAXCHILDREN];
 	struct delayed_work	leds;
+	struct delayed_work	init_work;
 };
 
 
···
 }
 EXPORT_SYMBOL_GPL(usb_hub_tt_clear_buffer);
 
-static void hub_power_on(struct usb_hub *hub)
+/* If do_delay is false, return the number of milliseconds the caller
+ * needs to delay.
+ */
+static unsigned hub_power_on(struct usb_hub *hub, bool do_delay)
 {
 	int port1;
 	unsigned pgood_delay = hub->descriptor->bPwrOn2PwrGood * 2;
+	unsigned delay;
 	u16 wHubCharacteristics =
 			le16_to_cpu(hub->descriptor->wHubCharacteristics);
 
···
 		set_port_feature(hub->hdev, port1, USB_PORT_FEAT_POWER);
 
 	/* Wait at least 100 msec for power to become stable */
-	msleep(max(pgood_delay, (unsigned) 100));
+	delay = max(pgood_delay, (unsigned) 100);
+	if (do_delay)
+		msleep(delay);
+	return delay;
 }
 
 static int hub_hub_status(struct usb_hub *hub,
···
 }
 
 enum hub_activation_type {
-	HUB_INIT, HUB_POST_RESET, HUB_RESUME, HUB_RESET_RESUME
+	HUB_INIT, HUB_INIT2, HUB_INIT3,
+	HUB_POST_RESET, HUB_RESUME, HUB_RESET_RESUME,
 };
+
+static void hub_init_func2(struct work_struct *ws);
+static void hub_init_func3(struct work_struct *ws);
 
 static void hub_activate(struct usb_hub *hub, enum hub_activation_type type)
 {
···
 	int port1;
 	int status;
 	bool need_debounce_delay = false;
+	unsigned delay;
+
+	/* Continue a partial initialization */
+	if (type == HUB_INIT2)
+		goto init2;
+	if (type == HUB_INIT3)
+		goto init3;
 
 	/* After a resume, port power should still be on.
 	 * For any other type of activation, turn it on.
 	 */
-	if (type != HUB_RESUME)
-		hub_power_on(hub);
+	if (type != HUB_RESUME) {
+
+		/* Speed up system boot by using a delayed_work for the
+		 * hub's initial power-up delays.  This is pretty awkward
+		 * and the implementation looks like a home-brewed sort of
+		 * setjmp/longjmp, but it saves at least 100 ms for each
+		 * root hub (assuming usbcore is compiled into the kernel
+		 * rather than as a module).  It adds up.
+		 *
+		 * This can't be done for HUB_RESUME or HUB_RESET_RESUME
+		 * because for those activation types the ports have to be
+		 * operational when we return.  In theory this could be done
+		 * for HUB_POST_RESET, but it's easier not to.
+		 */
+		if (type == HUB_INIT) {
+			delay = hub_power_on(hub, false);
+			PREPARE_DELAYED_WORK(&hub->init_work, hub_init_func2);
+			schedule_delayed_work(&hub->init_work,
+					msecs_to_jiffies(delay));
+			return;		/* Continues at init2: below */
+		} else {
+			hub_power_on(hub, true);
+		}
+	}
+ init2:
 
 	/* Check each port and set hub->change_bits to let khubd know
 	 * which ports need attention.
···
 	 * If any port-status changes do occur during this delay, khubd
 	 * will see them later and handle them normally.
 	 */
-	if (need_debounce_delay)
-		msleep(HUB_DEBOUNCE_STABLE);
+	if (need_debounce_delay) {
+		delay = HUB_DEBOUNCE_STABLE;
 
+		/* Don't do a long sleep inside a workqueue routine */
+		if (type == HUB_INIT2) {
+			PREPARE_DELAYED_WORK(&hub->init_work, hub_init_func3);
+			schedule_delayed_work(&hub->init_work,
+					msecs_to_jiffies(delay));
+			return;		/* Continues at init3: below */
+		} else {
+			msleep(delay);
+		}
+	}
+ init3:
 	hub->quiescing = 0;
 
 	status = usb_submit_urb(hub->urb, GFP_NOIO);
···
 	kick_khubd(hub);
 }
 
+/* Implement the continuations for the delays above */
+static void hub_init_func2(struct work_struct *ws)
+{
+	struct usb_hub *hub = container_of(ws, struct usb_hub, init_work.work);
+
+	hub_activate(hub, HUB_INIT2);
+}
+
+static void hub_init_func3(struct work_struct *ws)
+{
+	struct usb_hub *hub = container_of(ws, struct usb_hub, init_work.work);
+
+	hub_activate(hub, HUB_INIT3);
+}
+
 enum hub_quiescing_type {
 	HUB_DISCONNECT, HUB_PRE_RESET, HUB_SUSPEND
 };
···
 {
 	struct usb_device *hdev = hub->hdev;
 	int i;
+
+	cancel_delayed_work_sync(&hub->init_work);
 
 	/* khubd and related activity won't re-trigger */
 	hub->quiescing = 1;
···
 	hub->intfdev = &intf->dev;
 	hub->hdev = hdev;
 	INIT_DELAYED_WORK(&hub->leds, led_work);
+	INIT_DELAYED_WORK(&hub->init_work, NULL);
 	usb_get_intf(intf);
 
 	usb_set_intfdata (intf, hub);
···
 					i);
 				clear_port_feature(hdev, i,
 					USB_PORT_FEAT_C_OVER_CURRENT);
-				hub_power_on(hub);
+				hub_power_on(hub, true);
 			}
 
 			if (portchange & USB_PORT_STAT_C_RESET) {
···
 				dev_dbg (hub_dev, "overcurrent change\n");
 				msleep(500);	/* Cool down */
 				clear_hub_feature(hdev, C_HUB_OVER_CURRENT);
-                        	hub_power_on(hub);
+                        	hub_power_on(hub, true);
 			}
 		}