diff options
Diffstat (limited to 'kernel/Documentation/usb/anchors.txt')
| -rw-r--r-- | kernel/Documentation/usb/anchors.txt | 79 |
1 files changed, 79 insertions, 0 deletions
diff --git a/kernel/Documentation/usb/anchors.txt b/kernel/Documentation/usb/anchors.txt new file mode 100644 index 000000000..fe6a99a32 --- /dev/null +++ b/kernel/Documentation/usb/anchors.txt @@ -0,0 +1,79 @@ +What is anchor? +=============== + +A USB driver needs to support some callbacks requiring +a driver to cease all IO to an interface. To do so, a +driver has to keep track of the URBs it has submitted +to know they've all completed or to call usb_kill_urb +for them. The anchor is a data structure takes care of +keeping track of URBs and provides methods to deal with +multiple URBs. + +Allocation and Initialisation +============================= + +There's no API to allocate an anchor. It is simply declared +as struct usb_anchor. init_usb_anchor() must be called to +initialise the data structure. + +Deallocation +============ + +Once it has no more URBs associated with it, the anchor can be +freed with normal memory management operations. + +Association and disassociation of URBs with anchors +=================================================== + +An association of URBs to an anchor is made by an explicit +call to usb_anchor_urb(). The association is maintained until +an URB is finished by (successful) completion. Thus disassociation +is automatic. A function is provided to forcibly finish (kill) +all URBs associated with an anchor. +Furthermore, disassociation can be made with usb_unanchor_urb() + +Operations on multitudes of URBs +================================ + +usb_kill_anchored_urbs() +------------------------ + +This function kills all URBs associated with an anchor. The URBs +are called in the reverse temporal order they were submitted. +This way no data can be reordered. + +usb_unlink_anchored_urbs() +-------------------------- + +This function unlinks all URBs associated with an anchor. The URBs +are processed in the reverse temporal order they were submitted. +This is similar to usb_kill_anchored_urbs(), but it will not sleep. +Therefore no guarantee is made that the URBs have been unlinked when +the call returns. They may be unlinked later but will be unlinked in +finite time. + +usb_scuttle_anchored_urbs() +--------------------------- + +All URBs of an anchor are unanchored en masse. + +usb_wait_anchor_empty_timeout() +------------------------------- + +This function waits for all URBs associated with an anchor to finish +or a timeout, whichever comes first. Its return value will tell you +whether the timeout was reached. + +usb_anchor_empty() +------------------ + +Returns true if no URBs are associated with an anchor. Locking +is the caller's responsibility. + +usb_get_from_anchor() +--------------------- + +Returns the oldest anchored URB of an anchor. The URB is unanchored +and returned with a reference. As you may mix URBs to several +destinations in one anchor you have no guarantee the chronologically +first submitted URB is returned. |