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This adds documentation about the new usb anchor infrastructure. Signed-off-by: Oliver Neukum <oneukum@suse.de> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
51 lines
1.7 KiB
Plaintext
51 lines
1.7 KiB
Plaintext
What is anchor?
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===============
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A USB driver needs to support some callbacks requiring
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a driver to cease all IO to an interface. To do so, a
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driver has to keep track of the URBs it has submitted
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to know they've all completed or to call usb_kill_urb
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for them. The anchor is a data structure takes care of
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keeping track of URBs and provides methods to deal with
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multiple URBs.
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Allocation and Initialisation
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=============================
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There's no API to allocate an anchor. It is simply declared
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as struct usb_anchor. init_usb_anchor() must be called to
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initialise the data structure.
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Deallocation
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============
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Once it has no more URBs associated with it, the anchor can be
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freed with normal memory management operations.
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Association and disassociation of URBs with anchors
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===================================================
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An association of URBs to an anchor is made by an explicit
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call to usb_anchor_urb(). The association is maintained until
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an URB is finished by (successfull) completion. Thus disassociation
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is automatic. A function is provided to forcibly finish (kill)
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all URBs associated with an anchor.
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Furthermore, disassociation can be made with usb_unanchor_urb()
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Operations on multitudes of URBs
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================================
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usb_kill_anchored_urbs()
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------------------------
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This function kills all URBs associated with an anchor. The URBs
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are called in the reverse temporal order they were submitted.
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This way no data can be reordered.
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usb_wait_anchor_empty_timeout()
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-------------------------------
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This function waits for all URBs associated with an anchor to finish
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or a timeout, whichever comes first. Its return value will tell you
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whether the timeout was reached.
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