• Sarah Sharp's avatar
    Intel xhci: Limit number of active endpoints to 64. · 2cf95c18
    Sarah Sharp authored
    The Panther Point chipset has an xHCI host controller that has a limit to
    the number of active endpoints it can handle.  Ideally, it would signal
    that it can't handle anymore endpoints by returning a Resource Error for
    the Configure Endpoint command, but they don't.  Instead it needs software
    to keep track of the number of active endpoints, across configure endpoint
    commands, reset device commands, disable slot commands, and address device
    commands.
    
    Add a new endpoint context counter, xhci_hcd->num_active_eps, and use it
    to track the number of endpoints the xHC has active.  This gets a little
    tricky, because commands to change the number of active endpoints can
    fail.  This patch adds a new xHCI quirk for these Intel hosts, and the new
    code should not have any effect on other xHCI host controllers.
    
    Fail a new device allocation if we don't have room for the new default
    control endpoint.  Use the endpoint ring pointers to determine what
    endpoints were active before a Reset Device command or a Disable Slot
    command, and drop those once the command completes.
    
    Fail a configure endpoint command if it would add too many new endpoints.
    We have to be a bit over zealous here, and only count the number of new
    endpoints to be added, without subtracting the number of dropped
    endpoints.  That's because a second configure endpoint command for a
    different device could sneak in before we know if the first command is
    completed.  If the first command dropped resources, the host controller
    fails the command for some reason, and we're nearing the limit of
    endpoints, we could end up oversubscribing the host.
    
    To fix this race condition, when evaluating whether a configure endpoint
    command will fix in our bandwidth budget, only add the new endpoints to
    xhci->num_active_eps, and don't subtract the dropped endpoints.  Ignore
    changed endpoints (ones that are dropped and then re-added), as that
    shouldn't effect the host's endpoint resources.  When the configure
    endpoint command completes, subtract off the dropped endpoints.
    
    This may mean some configuration changes may temporarily fail, but it's
    always better to under-subscribe than over-subscribe resources.
    
    (Originally my plan had been to push the resource allocation down into the
    ring allocation functions.  However, that would cause us to allocate
    unnecessary resources when endpoints were changed, because the xHCI driver
    allocates a new ring for the changed endpoint, and only deletes the old
    ring once the Configure Endpoint command succeeds.  A further complication
    would have been dealing with the per-device endpoint ring cache.)
    Signed-off-by: default avatarSarah Sharp <sarah.a.sharp@linux.intel.com>
    2cf95c18
xhci.h 54.2 KB