USB_REQUEST

NAME

SYNOPSIS

struct usb_request {
  void * buf;
  unsigned length;
  dma_addr_t dma;
  void (* complete (struct usb_ep *ep,struct usb_request *req);
  void * context;
  struct list_head list;
  int status;
  unsigned actual;
};  

MEMBERS

buf

Buffer used for data. Always provide this; some controllers only use PIO, or don't use DMA for some endpoints.

length

Length of that data

dma

DMA address corresponding to 'buf'. If you don't set this field, and the usb controller needs one, it is responsible for mapping and unmapping the buffer.

complete

Function called when request completes

context

For use by the completion callback

list

For use by the gadget driver.

status

Reports completion code, zero or a negative errno. Normally, faults block the transfer queue from advancing until the completion callback returns. Code ``-ESHUTDOWN'' indicates completion caused by device disconnect, or when the driver disabled the endpoint.

actual

Reports actual bytes transferred. For reads (OUT transfers) this may be less than the requested length. If the short_not_ok flag is set, short reads are treated as errors even when status otherwise indicates successful completion. Note that for writes (IN transfers) the data bytes may still reside in a device-side FIFO.

DESCRIPTION

These are allocated/freed through the endpoint they're used with. The hardware's driver can add extra per-request data to the memory it returns, which often avoids separate memory allocations (potential failures), later when the request is queued.

Request flags affect request handling, such as whether a zero length packet is written (the ``zero'' flag), whether a short read should be treated as an error (blocking request queue advance, the ``short_not_ok'' flag), or hinting that an interrupt is not required (the ``no_interrupt'' flag, for use with deep request queues).

Bulk endpoints can use any size buffers, and can also be used for interrupt transfers. interrupt-only endpoints can be much less functional.  

ABOUT THIS DOCUMENT

Permission is granted to copy, distribute, and/or modify this document under the terms of the GNU Free Documentation License, version 1.2, or any later version published by the Free Software Foundation; with the Invariant Sections being the "GNU Free Documentation License", no Front-Cover Texts, and no Back-Cover Texts.

This documentation is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Free Documentation License for more details.

Note that certain sections of this document are merged into Linux kernel source code. That content is the bulk of [XRef to CORE]> and [XRef to UTILS]>, where the "GNU Free Documentation License" is identified as an alternate licence for its documentation.

If you have comments on the formatting of this manpage, then please contact Michael Still (mikal@stillhq.com).

This documentation was generated with kernel version 2.5.71.

Index

NAME

SYNOPSIS

MEMBERS

DESCRIPTION

ABOUT THIS DOCUMENT