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author | Linus Torvalds <torvalds@linux-foundation.org> | 2017-05-02 20:21:17 +0300 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-05-02 20:21:17 +0300 |
commit | c58d4055c054fc6dc72f1be8bc71bd6fff209e48 (patch) | |
tree | 56527e28fc65d74d6d5e8397c502ccc87a9ec99b /Documentation/driver-api/usb/anchors.rst | |
parent | ceb198bb007b84ead867e87a71ffe715c4412b15 (diff) | |
parent | 9bb0e9cb04c82d6bf0e72f3207307d621083b801 (diff) | |
download | linux-c58d4055c054fc6dc72f1be8bc71bd6fff209e48.tar.xz |
Merge tag 'docs-4.12' of git://git.lwn.net/linux
Pull documentation update from Jonathan Corbet:
"A reasonably busy cycle for documentation this time around. There is a
new guide for user-space API documents, rather sparsely populated at
the moment, but it's a start. Markus improved the infrastructure for
converting diagrams. Mauro has converted much of the USB documentation
over to RST. Plus the usual set of fixes, improvements, and tweaks.
There's a bit more than the usual amount of reaching out of
Documentation/ to fix comments elsewhere in the tree; I have acks for
those where I could get them"
* tag 'docs-4.12' of git://git.lwn.net/linux: (74 commits)
docs: Fix a couple typos
docs: Fix a spelling error in vfio-mediated-device.txt
docs: Fix a spelling error in ioctl-number.txt
MAINTAINERS: update file entry for HSI subsystem
Documentation: allow installing man pages to a user defined directory
Doc/PM: Sync with intel_powerclamp code behavior
zr364xx.rst: usb/devices is now at /sys/kernel/debug/
usb.rst: move documentation from proc_usb_info.txt to USB ReST book
convert philips.txt to ReST and add to media docs
docs-rst: usb: update old usbfs-related documentation
arm: Documentation: update a path name
docs: process/4.Coding.rst: Fix a couple of document refs
docs-rst: fix usb cross-references
usb: gadget.h: be consistent at kernel doc macros
usb: composite.h: fix two warnings when building docs
usb: get rid of some ReST doc build errors
usb.rst: get rid of some Sphinx errors
usb/URB.txt: convert to ReST and update it
usb/persist.txt: convert to ReST and add to driver-api book
usb/hotplug.txt: convert to ReST and add to driver-api book
...
Diffstat (limited to 'Documentation/driver-api/usb/anchors.rst')
-rw-r--r-- | Documentation/driver-api/usb/anchors.rst | 83 |
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 000000000000..4b248e691bd6 --- /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. |