• David Brownell's avatar
    [PATCH] ohci-hcd, queue fault recovery + rm DEBUG · 65e2da7e
    David Brownell authored
    This USB patch updates the OHCI driver:
    
      - converts to relying on td_list shadowing the hardware's
        schedule; only collecting the donelist needs dma_to_td(),
        and td list handling works much like EHCI or UHCI.
    
      - leaves faulted endpoint queues (bulk/intr) disabled until
        the relevant drivers had a chance to clean up.
    
      - fixes minor bugs (unreported) in the affected code:
          * byteswap problem when unlinking urbs ... symptom would
            be data toggle confusion (since 2.4.2x) on big-endian cpus
          * latent bug if folk unlinked queue in LIFO order, not FIFO
    
      - removes unnecessary debug code; mostly de-BUG()ged
    
    The interesting fix is the "leave queues halted" one.  As
    discussed on email a while back, this HCD fault handling
    policy (also followed by EHCI) is sufficient to let device
    drivers implement the two key fault handling policies that
    seem to be necessary:
    
        (a) Datagram style, where issues on one I/O won't affect
            the next unless the device halted the endpoint.  The
            device driver can ignore most errors other than -EPIPE.
    
        (b) Stream style, where for example it'd be wrong to ever
            let block N+1 overwrite block N on the disk.  Once
            the first URB fails, the rest would just be unlinked
            in the completion handler.
    
    As a consequence of using the td_list, you can now see urb
    queuing in action in the driverfs 'async' file.  At least, if
    you look at the right time, or use drivers (networking, etc)
    that queue (bulk) reads for a long time.
    65e2da7e
ohci-q.c 28.4 KB