ehci: Lower timer freq when the periodic schedule is idle

Lower the timer freq if no iso schedule packets complete for 64 frames in
a row.

We can safely do this, without adding latency, because:
1) If there is isoc traffic this will never trigger
2) For async handled interrupt packets (only usb-host), the completion handler
   will immediately schedule the frame_timer from a bh
3) All devices using NAK to signal no data for interrupt endpoints now use
   wakeup, which will immediately schedule the frame_timer from a bh

The advantage of this is that when we only have interrupt packets in the
periodic schedule, async_stepdown can do its work and significantly lower
the frequency at which the frame_timer runs.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/hw/usb/hcd-ehci.h b/hw/usb/hcd-ehci.h
index d8078f4..772870b 100644
--- a/hw/usb/hcd-ehci.h
+++ b/hw/usb/hcd-ehci.h
@@ -311,6 +311,7 @@ struct EHCIState {
 
     uint64_t last_run_ns;
     uint32_t async_stepdown;
+    uint32_t periodic_sched_active;
     bool int_req_by_async;
 };