[7/8] usb-hid: Move from NAK/polling to async packet handling

diff --git a/hw/usb/dev-hid.c b/hw/usb/dev-hid.c
index aa59ec4..69f89ff 100644
--- a/hw/usb/dev-hid.c
+++ b/hw/usb/dev-hid.c
@@ -45,6 +45,7 @@ 
 typedef struct USBHIDState {
     USBDevice dev;
     USBEndpoint *intr;
+    USBPacket *async_packet_pending;
     HIDState hid;
 } USBHIDState;
 
@@ -357,10 +358,30 @@  static const uint8_t qemu_keyboard_hid_report_descriptor[] = {
     0xc0,		/* End Collection */
 };
 
+static void usb_data_in_complete(HIDState *hs, USBPacket *p)
+{
+    uint8_t buf[p->iov.size];
+    int len = 0;
+
+    hid_set_next_idle(hs);
+    if (hs->kind == HID_MOUSE || hs->kind == HID_TABLET) {
+        len = hid_pointer_poll(hs, buf, p->iov.size);
+    } else if (hs->kind == HID_KEYBOARD) {
+        len = hid_keyboard_poll(hs, buf, p->iov.size);
+    }
+    usb_packet_copy(p, buf, len);
+}
+
 static void usb_hid_changed(HIDState *hs)
 {
     USBHIDState *us = container_of(hs, USBHIDState, hid);
 
+    if (us->async_packet_pending) {
+        us->async_packet_pending->status = USB_RET_SUCCESS; /* Clear ASYNC */
+        usb_data_in_complete(hs, us->async_packet_pending);
+        usb_packet_complete(&us->dev, us->async_packet_pending);
+        us->async_packet_pending = NULL;
+    }
     usb_wakeup(us->intr);
 }
 
@@ -455,8 +476,6 @@  static void usb_hid_handle_data(USBDevice *dev, USBPacket *p)
 {
     USBHIDState *us = DO_UPCAST(USBHIDState, dev, dev);
     HIDState *hs = &us->hid;
-    uint8_t buf[p->iov.size];
-    int len = 0;
 
     switch (p->pid) {
     case USB_TOKEN_IN:
@@ -465,16 +484,12 @@  static void usb_hid_handle_data(USBDevice *dev, USBPacket *p)
                 hid_pointer_activate(hs);
             }
             if (!hid_has_events(hs)) {
-                p->status = USB_RET_NAK;
+                assert(us->async_packet_pending == NULL);
+                us->async_packet_pending = p;
+                p->status = USB_RET_ASYNC;
                 return;
             }
-            hid_set_next_idle(hs);
-            if (hs->kind == HID_MOUSE || hs->kind == HID_TABLET) {
-                len = hid_pointer_poll(hs, buf, p->iov.size);
-            } else if (hs->kind == HID_KEYBOARD) {
-                len = hid_keyboard_poll(hs, buf, p->iov.size);
-            }
-            usb_packet_copy(p, buf, len);
+            usb_data_in_complete(hs, p);
         } else {
             goto fail;
         }
@@ -487,6 +502,14 @@  static void usb_hid_handle_data(USBDevice *dev, USBPacket *p)
     }
 }
 
+static void usb_hid_cancel_packet(USBDevice *dev, USBPacket *p)
+{
+    USBHIDState *us = DO_UPCAST(USBHIDState, dev, dev);
+
+    assert(us->async_packet_pending == p);
+    us->async_packet_pending = NULL;
+}
+
 static void usb_hid_handle_destroy(USBDevice *dev)
 {
     USBHIDState *us = DO_UPCAST(USBHIDState, dev, dev);
@@ -560,6 +583,7 @@  static void usb_hid_class_initfn(ObjectClass *klass, void *data)
     uc->handle_control = usb_hid_handle_control;
     uc->handle_data    = usb_hid_handle_data;
     uc->handle_destroy = usb_hid_handle_destroy;
+    uc->cancel_packet  = usb_hid_cancel_packet;
 }
 
 static void usb_tablet_class_initfn(ObjectClass *klass, void *data)