• Mathias Nyman's avatar
    xhci: update event ring dequeue pointer position to controller correctly · e30e9ad9
    Mathias Nyman authored
    The event ring dequeue pointer field (ERDP) in xHC hardware is used to
    inform controller how far the driver has processed events on the event
    ring.
    
    In the case all events are handled and event ring is empty then the
    address of the TRB after the last processed one should be written.
    This TRB is both the enqueue and dequeue pointer.
    
    But in case we are writing the ERDP in the middle of processing
    several events then ERDP field should be written with the "up to and
    including" address of the last handled event TRB.
    
    Currenly each ERDP write by driver is done as if all events are handled
    and ring is empty.
    
    Fix this by adjusting the order when software dequeue "inc_deq()"
    is called and hardware dequeue "xhci_update_erst_dequeue()" is updated.
    
    Details in xhci 1.2 specification section 4.9.4:
    
    "System software shall write the Event Ring Dequeue Pointer (ERDP)
     register to inform the xHC that it has completed the processing of Event
     TRBs up to and including the Event TRB referenced by the ERDP.
    
     The detection of a Cycle bit mismatch in an Event TRB processed by
     software indicates the location of the xHC Event Ring Enqueue Pointer
     and that the Event Ring is empty. Software shall write the ERDP with
     the address of this TRB to indicate that it has processed all Events
     in the ring"
    
    This change depends on fixes made to relocate inc_deq() calls captured
    in the below commits:
    
      commit 3321f84b ("xhci: simplify event ring dequeue tracking for
      transfer events")
    
      commit d1830364 ("xhci: Simplify event ring dequeue pointer update
      for port change events")
    
    Fixes: dc0ffbea ("usb: host: xhci: update event ring dequeue pointer on purpose")
    Signed-off-by: default avatarMathias Nyman <mathias.nyman@linux.intel.com>
    Signed-off-by: default avatarWesley Cheng <quic_wcheng@quicinc.com>
    Link: https://lore.kernel.org/r/20240217001017.29969-6-quic_wcheng@quicinc.comSigned-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    e30e9ad9
xhci-ring.c 132 KB