summaryrefslogtreecommitdiffstats
path: root/Documentation/driver-api/usb/anchors.rst
diff options
context:
space:
mode:
authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 10:05:51 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 10:05:51 +0000
commit5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch)
treea94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/driver-api/usb/anchors.rst
parentInitial commit. (diff)
downloadlinux-upstream/5.10.209.tar.xz
linux-upstream/5.10.209.zip
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/driver-api/usb/anchors.rst')
-rw-r--r--Documentation/driver-api/usb/anchors.rst83
1 files changed, 83 insertions, 0 deletions
diff --git a/Documentation/driver-api/usb/anchors.rst b/Documentation/driver-api/usb/anchors.rst
new file mode 100644
index 000000000..4b248e691
--- /dev/null
+++ b/Documentation/driver-api/usb/anchors.rst
@@ -0,0 +1,83 @@
+USB Anchors
+~~~~~~~~~~~
+
+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. :c:func:`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 :c:func:`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 :c:func:`usb_unanchor_urb`
+
+Operations on multitudes of URBs
+================================
+
+:c:func:`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.
+
+:c:func:`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 :c:func:`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.
+
+:c:func:`usb_scuttle_anchored_urbs`
+-----------------------------------
+
+All URBs of an anchor are unanchored en masse.
+
+:c:func:`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.
+
+:c:func:`usb_anchor_empty`
+--------------------------
+
+Returns true if no URBs are associated with an anchor. Locking
+is the caller's responsibility.
+
+:c:func:`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.