mirror of https://gitee.com/openkylin/linux.git
80 lines
2.6 KiB
Plaintext
80 lines
2.6 KiB
Plaintext
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.
|