1USB_SG_WAIT(9)                   USB Core APIs                  USB_SG_WAIT(9)
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NAME

6       usb_sg_wait - synchronously execute scatter/gather request
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SYNOPSIS

9       void usb_sg_wait(struct usb_sg_request * io);
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ARGUMENTS

12       io
13           request block handle, as initialized with usb_sg_init. some fields
14           become accessible when this call returns.
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CONTEXT

17       !in_interrupt ()
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DESCRIPTION

20       This function blocks until the specified I/O operation completes. It
21       leverages the grouping of the related I/O requests to get good transfer
22       rates, by queueing the requests. At higher speeds, such queuing can
23       significantly improve USB throughput.
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25       There are three kinds of completion for this function. (1) success,
26       where io->status is zero. The number of io->bytes transferred is as
27       requested. (2) error, where io->status is a negative errno value. The
28       number of io->bytes transferred before the error is usually less than
29       requested, and can be nonzero. (3) cancellation, a type of error with
30       status -ECONNRESET that is initiated by usb_sg_cancel.
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32       When this function returns, all memory allocated through usb_sg_init or
33       this call will have been freed. The request block parameter may still
34       be passed to usb_sg_cancel, or it may be freed. It could also be
35       reinitialized and then reused.
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DATA TRANSFER RATES

38       Bulk transfers are valid for full or high speed endpoints. The best
39       full speed data rate is 19 packets of 64 bytes each per frame, or 1216
40       bytes per millisecond. The best high speed data rate is 13 packets of
41       512 bytes each per microframe, or 52 KBytes per millisecond.
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43       The reason to use interrupt transfers through this API would most
44       likely be to reserve high speed bandwidth, where up to 24 KBytes per
45       millisecond could be transferred. That capability is less useful for
46       low or full speed interrupt endpoints, which allow at most one packet
47       per millisecond, of at most 8 or 64 bytes (respectively).
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49       It is not necessary to call this function to reserve bandwidth for
50       devices under an xHCI host controller, as the bandwidth is reserved
51       when the configuration or interface alt setting is selected.
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54Kernel Hackers Manual 2.6.         June 2019                    USB_SG_WAIT(9)
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