1STRUCT USB_REQUEST(9) Kernel Mode Gadget API STRUCT USB_REQUEST(9)
2
6 struct_usb_request - describes one i/o request
7
9 struct usb_request {
10 void * buf;
11 unsigned length;
12 dma_addr_t dma;
13 unsigned no_interrupt:1;
14 unsigned zero:1;
15 unsigned short_not_ok:1;
16 void (* complete) (struct usb_ep *ep,struct usb_request *req);
17 void * context;
18 struct list_head list;
19 int status;
20 unsigned actual;
21 };
22
24 buf
25 Buffer used for data. Always provide this; some controllers only
26 use PIO, or don´t use DMA for some endpoints.
27 length
29 Length of that data
30 dma
32 DMA address corresponding to ´buf´. If you don´t set this field,
33 and the usb controller needs one, it is responsible for mapping and
34 unmapping the buffer.
35 no_interrupt
37 If true, hints that no completion irq is needed. Helpful sometimes
38 with deep request queues that are handled directly by DMA
39 controllers.
40 zero
42 If true, when writing data, makes the last packet be “short” by
43 adding a zero length packet as needed;
44 short_not_ok
46 When reading data, makes short packets be treated as errors (queue
47 stops advancing till cleanup).
48 complete
50 Function called when request completes, so this request and its
51 buffer may be re-used. The function will always be called with
52 interrupts disabled, and it must not sleep. Reads terminate with a
53 short packet, or when the buffer fills, whichever comes first. When
54 writes terminate, some data bytes will usually still be in flight
55 (often in a hardware fifo). Errors (for reads or writes) stop the
56 queue from advancing until the completion function returns, so that
57 any transfers invalidated by the error may first be dequeued.
58 context
60 For use by the completion callback
61 list
63 For use by the gadget driver.
64 status
66 Reports completion code, zero or a negative errno. Normally, faults
67 block the transfer queue from advancing until the completion
68 callback returns. Code “-ESHUTDOWN” indicates completion caused by
69 device disconnect, or when the driver disabled the endpoint.
70 actual
72 Reports bytes transferred to/from the buffer. For reads (OUT
73 transfers) this may be less than the requested length. If the
74 short_not_ok flag is set, short reads are treated as errors even
75 when status otherwise indicates successful completion. Note that
76 for writes (IN transfers) some data bytes may still reside in a
77 device-side FIFO when the request is reported as complete.
78
80 These are allocated/freed through the endpoint they´re used with. The
81 hardware´s driver can add extra per-request data to the memory it
82 returns, which often avoids separate memory allocations (potential
83 failures), later when the request is queued.
84 Request flags affect request handling, such as whether a zero length
86 packet is written (the “zero” flag), whether a short read should be
87 treated as an error (blocking request queue advance, the “short_not_ok”
88 flag), or hinting that an interrupt is not required (the “no_interrupt”
89 flag, for use with deep request queues).
90 Bulk endpoints can use any size buffers, and can also be used for
92 interrupt transfers. interrupt-only endpoints can be much less
93 functional.
94
96 this is analagous to ´struct urb´ on the host side, except that it´s
97 thinner and promotes more pre-allocation.
98
100 David Brownell <dbrownell@users.sourceforge.net>
101 Author.
102
104Kernel Hackers Manual 2.6. June 2019 STRUCT USB_REQUEST(9)