Tribblix: manual page: usb_pipe

USB_PIPE_XOPEN(9F) Kernel Functions for Drivers USB_PIPE_XOPEN(9F)

NAME

usb_pipe_open, usb_pipe_xopen - Open a USB pipe to a device

SYNOPSIS

#include <sys/usb/usba.h>

int
usb_pipe_open(dev_info_t *dip, usb_ep_descr_t *endpoint,
usb_pipe_policy_t *pipe_policy, usb_flags_t flags,
usb_pipe_handle_t *pipe_handle);

int
usb_pipe_xopen(dev_info_t *dip, usb_ep_xdescr_t *extended_endpoint,
usb_pipe_policy_t *pipe_policy, usb_flags_t flags,
usb_pipe_handle_t *pipe_handle);

INTERFACE LEVEL

illumos DDI specific (illumos DDI)

PARAMETERS

dip Pointer to the device's dev_info structure.

endpoint Pointer to endpoint descriptor.

extended_endpoint
Pointer to an extended endpoint descriptor retrieved from
calling usb_ep_xdescr_fill(9F).

pipe_policy Pointer to pipe_policy. pipe_policy provides hints on
pipe usage.

flags USB_FLAGS_SLEEP is only flag that is recognized. Wait
for memory resources if not immediately available.

pipe_handle Address to where new pipe handle is returned. (The
handle is opaque.)

DESCRIPTION

A pipe is a logical connection to an endpoint on a USB device. The
usb_pipe_xopen() function creates such a logical connection and returns
an initialized handle which refers to that connection.

The USB 3.0 specification defines four endpoint types, each with a
corresponding type of pipe. Each of the four types of pipes uses its
physical connection resource differently. They are:

Control Pipe
Used for bursty, non-periodic, reliable, host-initiated
request/response communication, such as for command/status
operations. These are guaranteed to get approximately 10% of
frame time and will get more if needed and if available, but
there is no guarantee on transfer promptness. Bidirectional.

Bulk Pipe
Used for large, reliable, non-time-critical data transfers.
These get the bus on a bandwidth-available basis.
Unidirectional. Sample uses include printer data.

Interrupt Pipe
Used for sending or receiving small amounts of reliable data
infrequently but with bounded service periods, as for interrupt
handling. Unidirectional.

Isochronous Pipe
Used for large, unreliable, time-critical data transfers.
Boasts a guaranteed constant data rate as long as there is
data, but there are no retries of failed transfers. Interrupt
and isochronous data are together guaranteed 90% of frame time
as needed. Unidirectional. Sample uses include audio.

The type of endpoint to which a pipe connects (and therefore the pipe
type) is defined by the bmAttributes field of that pipe's endpoint
descriptor. (See usb_ep_descr(9S)).

Prior to the USB 3.0 specification, only the usb_ep_descr(9S) was
required to identify all of the attributes of a given pipe. Starting
with USB 3.0 there are additional endpoint companion descriptors
required to open a pipe. To support SuperSpeed devices, the new
usb_pipe_xopen() function must be used rather than the older
usb_pipe_open() function. The usb_ep_xdescr(9S) structure can be
automatically filled out and obtained by calling the
usb_ep_xdescr_fill(9F) function.

Opens to interrupt and isochronous pipes can fail if the required
bandwidth cannot be guaranteed.

The polling interval for periodic (interrupt or isochronous) pipes,
carried by the endpoint argument's bInterval field, must be within
range. Valid ranges are:

Full speed: range of 1-255 maps to 1-255 ms.

Low speed: range of 10-255 maps to 10-255 ms.

High speed: range of 1-16 maps to (2**(bInterval-1)) * 125us.

Super speed: range of 1-16 maps to (2**(bInterval-1)) * 125us.

Adequate bandwidth during transfers is guaranteed for all periodic
pipes which are opened successfully. Interrupt and isochronous pipes
have guaranteed latency times, so bandwidth for them is allocated when
they are opened. (Please refer to Sections 4.4.7 and 4.4.8 of the USB
3.1 specification which address isochronous and interrupt transfers.)
Opens of interrupt and isochronous pipes fail if inadequate bandwidth
is available to support their guaranteed latency time. Because
periodic pipe bandwidth is allocated on pipe open, open periodic pipes
only when needed.

The bandwidth required by a device varies based on polling interval,
the maximum packet size (wMaxPacketSize) and the device speed.
Unallocated bandwidth remaining for new devices depends on the
bandwidth already allocated for previously opened periodic pipes.

The pipe_policy parameter provides a hint as to pipe usage and must be
specified. It is a usb_pipe_policy_t which contains the following
fields:

uchar_t pp_max_async_reqs:

The pp_max_async_reqs member is a hint indicating how many asynchronous
operations requiring their own kernel thread will be concurrently in
progress, the highest number of threads ever needed at one time. Allow
at least one for synchronous callback handling and as many as are
needed to accommodate the anticipated parallelism of asynchronous*
calls to the following functions: usb_pipe_close(9F), usb_set_cfg(9F),
usb_set_alt_if(9F), usb_clr_feature(9F), usb_pipe_reset(9F),
usb_pipe_drain_reqs(9F), usb_pipe_stop_intr_polling(9F), and
usb_pipe_stop_isoc_polling(9F).

Setting to too small a value can deadlock the pipe. Asynchronous calls
are calls made without the USB_FLAGS_SLEEP flag being passed. Note
that a large number of callbacks becomes an issue mainly when blocking
functions are called from callback handlers.

The control pipe to the default endpoints (endpoints for both
directions with addr 0, sometimes called the default control pipe or
default pipe) comes pre-opened by the hub. A client driver receives
the default control pipe handle through usb_get_dev_data(9F). A client
driver cannot open the default control pipe manually. Note that the
same control pipe may be shared among several drivers when a device has
multiple interfaces and each interface is operated by its own driver.

All explicit pipe opens are exclusive; attempts to open an opened pipe
fail.

On success, the pipe_handle argument points to an opaque handle of the
opened pipe. On failure, it is set to NULL.

CONTEXT

May be called from user or kernel context regardless of arguments. May
also be called from interrupt context if the USB_FLAGS_SLEEP option is
not set.

RETURN VALUES

USB_SUCCESS
Open succeeded.

USB_NO_RESOURCES
Insufficient resources were available.

USB_NO_BANDWIDTH
Insufficient bandwidth available. (isochronous and interrupt
pipes).

USB_INVALID_CONTEXT
Called from interrupt handler with USB_FLAGS_SLEEP set.

USB_INVALID_ARGS
dip and/or pipe_handle is NULL. Pipe_policy is NULL.

USB_INVALID_PERM
Endpoint is NULL, signifying the default control pipe. A
client driver cannot open the default control pipe.

USB_NOT_SUPPORTED
Isochronous or interrupt endpoint with maximum packet size of
zero is not supported.

USB_HC_HARDWARE_ERROR
Host controller is in an error state.

USB_FAILURE
Pipe is already open. Host controller not in an operational
state. Polling interval (Bep_descr bInterval field) is out of
range (intr or isoc pipes).

The device referred to by dip is at least a SuperSpeed device
and the older usb_pipe_open() function was used.

EXAMPLES

usb_ep_data_t *ep_data;
usb_ep_xdescr_t ep_xdescr;
usb_pipe_policy_t policy;
usb_pipe_handle_t pipe;
usb_client_dev_data_t *reg_data;
uint8_t interface = 1;
uint8_t alternate = 1;
uint8_t first_ep_number = 0;

/* Initialize pipe policy. */
bzero(policy, sizeof(usb_pipe_policy_t));
policy.pp_max_async_requests = 2;

/* Get tree of descriptors for device. */
if (usb_get_dev_data(dip, USBDRV_VERSION, ®_data,
USB_FLAGS_ALL_DESCR, 0) != USB_SUCCESS) {
...
}

/* Get first interrupt-IN endpoint. */
ep_data = usb_lookup_ep_data(dip, reg_data, interface, alternate,
first_ep_number, USB_EP_ATTR_INTR, USB_EP_DIR_IN);
if (ep_data == NULL) {
...
}

/* Translate the ep_data into the filled in usb_ep_xdescr_t */
if (usb_ep_xdescr_fill(USB_EP_XDESCR_CURRENT_VERSION, dip,
ep_data, &ep_xdescr) != USB_SUCCESS) {
...
}

/* Open the pipe. Get handle to pipe back in 5th argument. */
if (usb_pipe_open(dip, &ep_data.ep_descr
&policy, USB_FLAGS_SLEEP, &pipe) != USB_SUCCESS) {
...
}