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¶
void * buf
Buffer used for data. Always provide this; some
controllers only use PIO, or don't use DMA for some endpoints.
unsigned length
Length of that data
dma_addr_t 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.
struct scatterlist * sg
a scatterlist for SG-capable controllers.
unsigned num_sgs
number of SG entries
unsigned num_mapped_sgs
number of SG entries mapped to DMA (internal)
unsigned:16 stream_id
The stream id, when USB3.0 bulk streams are being
used
unsigned:1 no_interrupt
If true, hints that no completion irq is needed. Helpful
sometimes with deep request queues that are handled directly by DMA
controllers.
unsigned:1 zero
If true, when writing data, makes the last packet be
“short” by adding a zero length packet as needed;
unsigned:1 short_not_ok
When reading data, makes short packets be treated as
errors (queue stops advancing till cleanup).
void (*)(struct usb_ep *ep,struct usb_request *req) 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.
void * context
For use by the completion callback
struct list_head list
For use by the gadget driver.
int 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.
unsigned 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@users.sourceforge.net>
Author.