Implement debounce sequence according to USB 2.0 specs.

This replaces waiting a fixed time of 300ms for the device power to
stabilize. In the ideal case this reduces the boot time by 200ms per
connected device (including internal hubs).

This is very similar to what Linux implements and we use the same time
values. An interval of 25ms is used to check for connection state
changes, the stable time is at least 100ms as per the USB specs and the
whole process times out after 1.5 seconds.

src/add-ons/kernel/bus_managers/usb/Hub.cpp

@@ -221,8 +221,13 @@ Hub::Explore(change_item **changeList)
 
 				int32 retry = 2;
 				while (retry--) {
-					// wait some time for the device to power up
+					// wait for stable device power
-					snooze(USB_DELAY_DEVICE_POWER_UP);
+					result = _DebouncePort(i);
+					if (result != B_OK) {
+						TRACE_ERROR("debouncing port %" B_PRId32
+							" failed: %s\n", i, strerror(result));
+						break;
+					}
 
 					// reset the port, this will also enable it
 					result = ResetPort(i);
@@ -433,3 +438,38 @@ Hub::BuildDeviceName(char *string, uint32 *index, size_t bufferSize,
 
 	return B_OK;
 }
+
+
+status_t
+Hub::_DebouncePort(uint8 index)
+{
+	uint32 timeout = 0;
+	uint32 stableTime = 0;
+	while (timeout < USB_DEBOUNCE_TIMEOUT) {
+		snooze(USB_DEBOUNCE_CHECK_INTERVAL);
+		timeout += USB_DEBOUNCE_CHECK_INTERVAL;
+
+		status_t result = UpdatePortStatus(index);
+		if (result != B_OK)
+			return result;
+
+		if ((fPortStatus[index].change & PORT_STATUS_CONNECTION) == 0) {
+			stableTime += USB_DEBOUNCE_CHECK_INTERVAL;
+			if (stableTime >= USB_DEBOUNCE_STABLE_TIME)
+				return B_OK;
+			continue;
+		}
+
+		// clear the connection change and reset stable time
+		result = DefaultPipe()->SendRequest(USB_REQTYPE_CLASS
+			| USB_REQTYPE_OTHER_OUT, USB_REQUEST_CLEAR_FEATURE,
+			C_PORT_CONNECTION, index + 1, 0, NULL, 0, NULL);
+		if (result != B_OK)
+			return result;
+
+		TRACE("got connection change during debounce, resetting stable time\n");
+		stableTime = 0;
+	}
+
+	return B_TIMED_OUT;
+}

src/add-ons/kernel/bus_managers/usb/usb_private.h

@@ -610,6 +610,8 @@ virtual	status_t						BuildDeviceName(char *string,
 											Device *device);
 
 private:
+		status_t						_DebouncePort(uint8 index);
+
 		InterruptPipe *					fInterruptPipe;
 		usb_hub_descriptor				fHubDescriptor;
 

src/add-ons/kernel/bus_managers/usb/usbspec_private.h

@@ -19,7 +19,6 @@
 #define USB_MAX_PORT_COUNT				16
 
 #define USB_DELAY_BUS_RESET				100000
-#define USB_DELAY_DEVICE_POWER_UP		300000
 #define USB_DELAY_HUB_POWER_UP			200000
 #define USB_DELAY_PORT_RESET			50000
 #define USB_DELAY_PORT_RESET_RECOVERY	250000
@@ -28,6 +27,10 @@
 #define USB_DELAY_SET_CONFIGURATION		50000
 #define USB_DELAY_HUB_EXPLORE			1000000
 
+#define USB_DEBOUNCE_TIMEOUT			1500000
+#define USB_DEBOUNCE_CHECK_INTERVAL		25000
+#define USB_DEBOUNCE_STABLE_TIME		100000
+
 // For bandwidth calculation
 #define	USB_BW_HOST_DELAY					1000
 #define	USB_BW_SETUP_LOW_SPEED_PORT_DELAY	333