| struct_usb_request(9) - phpMan
STRUCT USB_REQUEST(9) Kernel Mode Gadget API STRUCT USB_REQUEST(9)
NAME
struct_usb_request - describes one i/o request
SYNOPSIS
struct usb_request {
void * buf;
unsigned length;
dma_addr_t dma;
struct scatterlist * sg;
unsigned num_sgs;
unsigned num_mapped_sgs;
unsigned stream_id:16;
unsigned no_interrupt:1;
unsigned zero:1;
unsigned short_not_ok:1;
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.
sg
a scatterlist for SG-capable controllers.
num_sgs
number of SG entries
num_mapped_sgs
number of SG entries mapped to DMA (internal)
stream_id
The stream id, when USB3.0 bulk streams are being used
no_interrupt
If true, hints that no completion irq is needed. Helpful sometimes with deep request
queues that are handled directly by DMA controllers.
zero
If true, when writing data, makes the last packet be “short” by adding a zero length
packet as needed;
short_not_ok
When reading data, makes short packets be treated as errors (queue stops advancing
till cleanup).
complete
Function called when request completes, so this request and its buffer may be re-used.
The function will always be called with interrupts disabled, and it must not sleep.
Reads terminate with a short packet, or when the buffer fills, whichever comes first.
When writes terminate, some data bytes will usually still be in flight (often in a
hardware fifo). Errors (for reads or writes) stop the queue from advancing until the
completion function returns, so that any transfers invalidated by the error may first
be dequeued.
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 bytes transferred to/from the buffer. 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) some data bytes may still reside in a device-side FIFO
when the request is reported as complete.
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.
NOTE
this is analogous to 'struct urb' on the host side, except that it's thinner and promotes
more pre-allocation.
AUTHOR
David Brownell <dbrownell AT users.net>
Author.
COPYRIGHT
Kernel Hackers Manual 4.8. January 2017 STRUCT USB_REQUEST(9)
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