freebsd-skq/share/man/man4/usb2_core.4

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.Dd September 20, 2008
.Dt USB2_CORE 4
.Os
.
.Sh NAME
.
.
.Nm usb2_core
.
.Nd "USB core functions"
.
.
.Sh SYNOPSIS
To compile this module into the kernel, place the following line in
your kernel configuration file:
.Bd -ragged -offset indent
.Cd "device usb2_core"
.Ed
.Pp
To load the module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
usb2_core_load="YES"
.Ed
.
.Pp
Here is a list of commonly used functions:
.Pp
.
.Ft "usb2_error_t"
.Fo "usb2_transfer_setup"
.Fa "udev"
.Fa "ifaces"
.Fa "pxfer"
.Fa "setup_start"
.Fa "n_setup"
.Fa "priv_sc"
.Fa "priv_mtx"
.Fc
.
.Ft "void"
.Fo "usb2_transfer_unsetup"
.Fa "pxfer"
.Fa "n_setup"
.Fc
.
.Ft "void"
.Fo "usb2_transfer_start"
.Fa "xfer"
.Fc
.
.Ft "void"
.Fo "usb2_transfer_stop"
.Fa "xfer"
.Fc
.
.Ft "void"
.Fo "usb2_transfer_drain"
.Fa "xfer"
.Fc
.
.
.Sh DESCRIPTION
The
.Nm
module implements the core functionality of the USB standard and many
helper functions to make USB device driver programming easier and more
safe.
.
The
.Nm
module supports both USB Host and USB Device side mode!
.
.Sh USB TRANSFER MANAGEMENT FUNCTIONS
The USB standard defines four types of USB transfers.
.
Control transfers, Bulk transfers, Interrupt transfers and Isochronous
transfers.
.
All the transfer types are managed using the following five functions:
.
.Pp
.
.Fn usb2_transfer_setup
This function will allocate memory for and initialise an array of USB
transfers and all required DMA memory.
.
This function can sleep or block waiting for resources to become
available.
.Fa udev
is a pointer to "struct usb2_device".
.Fa ifaces
is an array of interface index numbers to use. See "if_index".
.Fa pxfer
is a pointer to an array of USB transfer pointers that are initialized
to NULL, and then pointed to allocated USB transfers.
.Fa setup_start
is a pointer to an array of USB config structures.
.Fa n_setup
is a number telling the USB system how many USB transfers should be
setup.
.Fa priv_sc
is the private softc pointer, which will be used to initialize
"xfer->priv_sc".
.Fa priv_mtx
is the private mutex protecting the transfer structure and the
softc. This pointer is used to initialize "xfer->priv_mtx".
This function returns
zero upon success. A non-zero return value indicates failure.
.
.Pp
.
.Fn usb2_transfer_unsetup
This function will release the given USB transfers and all allocated
resources associated with these USB transfers. 
.Fa pxfer
is a pointer to an array of USB transfer pointers, that may be NULL,
that should be freed by the USB system.
.Fa n_setup
is a number telling the USB system how many USB transfers should be
unsetup.
.
This function can sleep waiting for USB transfers to complete.
.
This function is NULL safe with regard to the USB transfer structure
pointer.
.
It is not allowed to call this function from the USB transfer
callback.
.
.Pp
.
.Fn usb2_transfer_start
This function will start the USB transfer pointed to by
.Fa xfer,
if not already started.
.
This function is always non-blocking and must be called with the
so-called private USB mutex locked.
.
This function is NULL safe with regard to the USB transfer structure
pointer.
.
.Pp
.
.Fn usb2_transfer_stop
This function will stop the USB transfer pointed to by
.Fa xfer,
if not already stopped.
.
This function is always non-blocking and must be called with the
so-called private USB mutex locked.
.
This function can return before the USB callback has been called.
.
This function is NULL safe with regard to the USB transfer structure
pointer.
.
If the transfer was in progress, the callback will called with
"USB_ST_ERROR" and "xfer->error = USB_ERR_CANCELLED".
.
.Pp
.
.Fn usb2_transfer_drain
This function will stop an USB transfer, if not already stopped and
wait for any additional USB hardware operations to complete.
.
Buffers that are loaded into DMA using "usb2_set_frame_data()" can
safely be freed after that this function has returned.
.
This function can block the caller and will not return before the USB
callback has been called.
.
This function is NULL safe with regard to the USB transfer structure
pointer.
.
.Sh USB TRANSFER CALLBACK
.
The USB callback has three states.
.
USB_ST_SETUP, USB_ST_TRANSFERRED and USB_ST_ERROR. USB_ST_SETUP is the
initial state.
.
After the callback has been called with this state it will always be
called back at a later stage in one of the other two states.
.
In the USB_ST_ERROR state the "error" field of the USB transfer
structure is set to the error cause.
.
The USB callback should not restart the USB transfer in case the error
cause is USB_ERR_CANCELLED.
.
The USB callback is protected from recursion.
.
That means one can start and stop whatever transfer from the callback
of another transfer one desires.
.
Also the transfer that is currently called back.
.
Recursion is handled like this that when the callback that wants to
recurse returns it is called one more time.
.
.
.Pp
.
.Fn usb2_start_hardware
This function should only be called from within the USB callback and
is used to start the USB hardware.
.
Typical parameters that should be set in the USB transfer structure
before this function is called are "frlengths[]", "nframes" and
"frbuffers[]".
.
An USB transfer can have multiple frames consisting of one or more USB
packets making up an I/O vector for all USB transfer types.
.
After the USB transfer is complete "frlengths[]" is updated to the
actual USB transfer length for the given frame.
.Bd -literal -offset indent
void
usb2_default_callback(struct usb2_xfer *xfer)
{
	switch (USB_GET_STATE(xfer)) {
	case USB_ST_SETUP: 
		/*
		 * Setup xfer->frlengths[], xfer->nframes
		 * and write data to xfer->frbuffers[], if any
		 */
		usb2_start_hardware(xfer);
		break;

	case USB_ST_TRANSFERRED: 
		/* 
		 * Read	data from xfer->frbuffers[], if any.
		 * "xfer->frlengths[]" should now have been
		 * updated to the actual length.
		 */
		break;

	default: /* Error */
		/*
		 * Print error message and clear stall 
		 * for example.
		 */
		break;
	}
	/* 
	 * Here it is safe to do something without the private 
	 * USB mutex locked.
	 */
	return;
}
.Ed
.
.Sh USB CONTROL TRANSFERS
An USB control transfer has three parts.
.
First the SETUP packet, then DATA packet(s) and then a STATUS
packet.
.
The SETUP packet is always pointed to by "xfer->frbuffers[0]" and the
length is stored in "xfer->frlengths[0]" also if there should not be
sent any SETUP packet! If an USB control transfer has no DATA stage,
then "xfer->nframes" should be set to 1.
.
Else the default value is "xfer->nframes" equal to 2.
.
.Bd -literal -offset indent

Example1: SETUP + STATUS
 xfer->nframes = 1;
 xfer->frlenghts[0] = 8;
 usb2_start_hardware(xfer);

Example2: SETUP + DATA + STATUS
 xfer->nframes = 2;
 xfer->frlenghts[0] = 8;
 xfer->frlenghts[1] = 1;
 usb2_start_hardware(xfer);

Example3: SETUP + DATA + STATUS - split
1st callback:
 xfer->nframes = 1;
 xfer->frlenghts[0] = 8;
 usb2_start_hardware(xfer);

2nd callback:
 /* IMPORTANT: frbuffers[0] must still point at the setup packet! */
 xfer->nframes = 2;
 xfer->frlenghts[0] = 0;
 xfer->frlenghts[1] = 1;
 usb2_start_hardware(xfer);

Example4: SETUP + STATUS - split
1st callback:
 xfer->nframes = 1;
 xfer->frlenghts[0] = 8;
 xfer->flags.manual_status = 1;
 usb2_start_hardware(xfer);

2nd callback:
 xfer->nframes = 1;
 xfer->frlenghts[0] = 0;
 xfer->flags.manual_status = 0;
 usb2_start_hardware(xfer);

.Ed
.Sh USB TRANSFER CONFIG
To simply the search for endpoints the
.Nm
module defines a USB config structure where it is possible to specify
the characteristics of the wanted endpoint.
.Bd -literal -offset indent

struct usb2_config { 
	bufsize,
	callback
	direction,
	endpoint,
	frames,
	index flags,
	interval,
	timeout,
	type,
};

.Ed
.
.Pp
.Fa type
field selects the USB pipe type.
.
Valid values are: UE_INTERRUPT, UE_CONTROL, UE_BULK,
UE_ISOCHRONOUS.
.
The special value UE_BULK_INTR will select BULK and INTERRUPT pipes.
.
This field is mandatory.
.
.Pp
.Fa endpoint
field selects the USB endpoint number.
.
A value of 0xFF, "-1" or "UE_ADDR_ANY" will select the first matching
endpoint.
.
This field is mandatory.
.
.Pp
.Fa direction
field selects the USB endpoint direction.
.
A value of "UE_DIR_ANY" will select the first matching endpoint.
.
Else valid values are: "UE_DIR_IN" and "UE_DIR_OUT".
.
"UE_DIR_IN" and "UE_DIR_OUT" can be binary OR'ed by "UE_DIR_SID" which
means that the direction will be swapped in case of
USB_MODE_DEVICE.
.
Note that "UE_DIR_IN" refers to the data transfer direction of the
"IN" tokens and "UE_DIR_OUT" refers to the data transfer direction of
the "OUT" tokens.
.
This field is mandatory.
.
.Pp
.Fa interval
field selects the interrupt interval.
.
The value of this field is given in milliseconds and is independent of
device speed.
.
Depending on the endpoint type, this field has different meaning:
.Bl -tag
.It UE_INTERRUPT
"0" use the default interrupt interval based on endpoint descriptor.
"Else" use the given value for polling rate.
.It UE_ISOCHRONOUS
"0" use default. "Else" the value is ignored.
.It UE_BULK
.It UE_CONTROL
"0" no transfer pre-delay. "Else" a delay as given by this field in
milliseconds is inserted before the hardware is started when
"usb2_start_hardware()" is called.
.Pp
NOTE: The transfer timeout, if any, is started after that the
pre-delay has elapsed!
.El
.
.Pp
.Fa timeout
field, if non-zero, will set the transfer timeout in milliseconds. If
the "timeout" field is zero and the transfer type is ISOCHRONOUS a
timeout of 250ms will be used.
.
.Pp
.Fa frames
field sets the maximum number of frames. If zero is specified it will
yield the following results:
.Bl -tag
.It UE_BULK
xfer->nframes = 1;
.It UE_INTERRUPT
xfer->nframes = 1;
.It UE_CONTROL
xfer->nframes = 2;
.It UE_ISOCHRONOUS
Not allowed. Will cause an error.
.El
.
.Pp
.Fa ep_index
field allows you to give a number, in case more endpoints match the
description, that selects which matching "ep_index" should be used.
.
.Pp
.Fa if_index
field allows you to select which of the interface numbers in the
"ifaces" array parameter passed to "usb2_transfer_setup" that should
be used when setting up the given USB transfer.
.
.Pp
.Fa flags
field has type "struct usb2_xfer_flags" and allows one to set initial
flags an USB transfer. Valid flags are:
.Bl -tag
.It force_short_xfer
This flag forces the last transmitted USB packet to be short.  A short
packet has a length of less than "xfer->max_packet_size", which
derives from "wMaxPacketSize". This flag can be changed during
operation.
.It short_xfer_ok
This flag allows the received transfer length, "xfer->actlen" to be
less than "xfer->sumlen" upon completion of a transfer.  This flag can
be changed during operation.
.It pipe_bof
This flag causes a failing USB transfer to remain first in the PIPE
queue except in the case of "xfer->error" equal to
"USB_ERR_CANCELLED". No other USB transfers in the affected PIPE queue
will be started until either:
.Bl -tag
.It 1
The failing USB transfer is stopped using "usb2_transfer_stop()".
.It 2
The failing USB transfer performs a successful transfer.
.El
The purpose of this flag is to avoid races when multiple transfers are
queued for execution on an USB endpoint, and the first executing
transfer fails leading to the need for clearing of stall for
example.
.
In this case this flag is used to prevent the following USB transfers
from being executed at the same time the clear-stall command is
executed on the USB control endpoint.
.
This flag can be changed during operation.
.Pp
"BOF" is short for "Block On Failure"
.Pp
NOTE: This flag should be set on all BULK and INTERRUPT USB transfers
which use an endpoint that can be shared between userland and kernel.
.
.
.It proxy_buffer
Setting this flag will cause that the total buffer size will be
rounded up to the nearest atomic hardware transfer size.
.
The maximum data length of any USB transfer is always stored in the
"xfer->max_data_length".
.
For control transfers the USB kernel will allocate additional space
for the 8-bytes of SETUP header.
.
These 8-bytes are not counted by the "xfer->max_data_length"
variable.
.
This flag can not be changed during operation.
.
.
.It ext_buffer
Setting this flag will cause that no data buffer will be
allocated.
.
Instead the USB client must supply a data buffer.
.
This flag can not be changed during operation.
.
.
.It manual_status
Setting this flag prevents an USB STATUS stage to be appended to the
end of the USB control transfer.
.
If no control data is transferred this flag must be cleared.
.
Else an error will be returned to the USB callback.
.
This flag is mostly useful for the USB device side.
.
This flag can be changed during operation.
.
.
.It no_pipe_ok
Setting this flag causes the USB_ERR_NO_PIPE error to be ignored. This
flag can not be changed during operation.
.
.
.It stall_pipe
.Bl -tag
.It Device Side Mode
Setting this flag will cause STALL pids to be sent to the endpoint
belonging to this transfer before the transfer is started.
.
The transfer is started at the moment the host issues a clear-stall
command on the STALL'ed endpoint.
.
This flag can be changed during operation.
.It Host Side Mode
Setting this flag will cause a clear-stall control request to be
executed on the endpoint before the USB transfer is started.
.El
.Pp
If this flag is changed outside the USB callback function you have to
use the "usb2_transfer_set_stall()" and "usb2_transfer_clear_stall()"
functions !
.
.El
.Pp
.Fa bufsize
field sets the total buffer size in bytes.
.
If this field is zero, "wMaxPacketSize" will be used, multiplied by
the "frames" field if the transfer type is ISOCHRONOUS.
.
This is useful for setting up interrupt pipes.
.
This field is mandatory.
.Pp
NOTE: For control transfers "bufsize" includes the length of the
request structure.
.
.Pp
.Fa callback
pointer sets the USB callback. This field is mandatory.
.
.
.Sh USB LINUX COMPAT LAYER
The
.Nm
module supports the Linux USB API.
.
.
.
.
.Sh USB SECURITY MODEL
.
.
The
.Nm
module implements fine grained read and write access based on username
and group.
.
Access is granted at four levels:
.
.Bl -tag
.It Level 4 - USB interface
USB interfaces can be given individual access rights.
.It Level 3 - USB device
USB devices can be given individual access rights.
.It Level 2 - USB BUS
USB busses can be given individual access rights.
.It Level 1 - USB
USB as a whole can be given individual access rights.
.El
.Pp
The
.Nm
module will search for access rights starting at level 4 continuing
downwards to USB at level 1.
.
For critical applications you should be aware that the outgoing serial
BUS traffic will be broadcasted to all USB devices.
.
For absolute security USB devices that require different access rights
should not be placed on the same USB BUS or controller.
.
If connected to the same USB bus, it is possible that a USB device can
sniff and intercept the communication of another USB device.
.
Using USB HUBs will not solve this problem.
.Sh SEE ALSO
.Xr usb2_controller 4
.Xr usbconfig 8
.Sh STANDARDS
The
.Nm
module complies with the USB 2.0 standard.
.Sh HISTORY
The
.Nm
module has been inspired by the NetBSD USB stack initially written by
Lennart Augustsson. The
.Nm
module was written by
.An Hans Petter Selasky Aq hselasky@freebsd.org .