mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-12-06 02:24:14 +08:00
dd0b38d8ee
This is a conversion of the USB documentation to the Sphinx format. No content was altered or reformatted. Signed-off-by: Oliver <oneukum@suse.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
749 lines
30 KiB
ReStructuredText
749 lines
30 KiB
ReStructuredText
===========================
|
|
The Linux-USB Host Side API
|
|
===========================
|
|
|
|
Introduction to USB on Linux
|
|
============================
|
|
|
|
A Universal Serial Bus (USB) is used to connect a host, such as a PC or
|
|
workstation, to a number of peripheral devices. USB uses a tree
|
|
structure, with the host as the root (the system's master), hubs as
|
|
interior nodes, and peripherals as leaves (and slaves). Modern PCs
|
|
support several such trees of USB devices, usually
|
|
a few USB 3.0 (5 GBit/s) or USB 3.1 (10 GBit/s) and some legacy
|
|
USB 2.0 (480 MBit/s) busses just in case.
|
|
|
|
That master/slave asymmetry was designed-in for a number of reasons, one
|
|
being ease of use. It is not physically possible to mistake upstream and
|
|
downstream or it does not matter with a type C plug (or they are built into the
|
|
peripheral). Also, the host software doesn't need to deal with
|
|
distributed auto-configuration since the pre-designated master node
|
|
manages all that.
|
|
|
|
Kernel developers added USB support to Linux early in the 2.2 kernel
|
|
series and have been developing it further since then. Besides support
|
|
for each new generation of USB, various host controllers gained support,
|
|
new drivers for peripherals have been added and advanced features for latency
|
|
measurement and improved power management introduced.
|
|
|
|
Linux can run inside USB devices as well as on the hosts that control
|
|
the devices. But USB device drivers running inside those peripherals
|
|
don't do the same things as the ones running inside hosts, so they've
|
|
been given a different name: *gadget drivers*. This document does not
|
|
cover gadget drivers.
|
|
|
|
USB Host-Side API Model
|
|
=======================
|
|
|
|
Host-side drivers for USB devices talk to the "usbcore" APIs. There are
|
|
two. One is intended for *general-purpose* drivers (exposed through
|
|
driver frameworks), and the other is for drivers that are *part of the
|
|
core*. Such core drivers include the *hub* driver (which manages trees
|
|
of USB devices) and several different kinds of *host controller
|
|
drivers*, which control individual busses.
|
|
|
|
The device model seen by USB drivers is relatively complex.
|
|
|
|
- USB supports four kinds of data transfers (control, bulk, interrupt,
|
|
and isochronous). Two of them (control and bulk) use bandwidth as
|
|
it's available, while the other two (interrupt and isochronous) are
|
|
scheduled to provide guaranteed bandwidth.
|
|
|
|
- The device description model includes one or more "configurations"
|
|
per device, only one of which is active at a time. Devices are supposed
|
|
to be capable of operating at lower than their top
|
|
speeds and may provide a BOS descriptor showing the lowest speed they
|
|
remain fully operational at.
|
|
|
|
- From USB 3.0 on configurations have one or more "functions", which
|
|
provide a common functionality and are grouped together for purposes
|
|
of power management.
|
|
|
|
- Configurations or functions have one or more "interfaces", each of which may have
|
|
"alternate settings". Interfaces may be standardized by USB "Class"
|
|
specifications, or may be specific to a vendor or device.
|
|
|
|
USB device drivers actually bind to interfaces, not devices. Think of
|
|
them as "interface drivers", though you may not see many devices
|
|
where the distinction is important. *Most USB devices are simple,
|
|
with only one function, one configuration, one interface, and one alternate
|
|
setting.*
|
|
|
|
- Interfaces have one or more "endpoints", each of which supports one
|
|
type and direction of data transfer such as "bulk out" or "interrupt
|
|
in". The entire configuration may have up to sixteen endpoints in
|
|
each direction, allocated as needed among all the interfaces.
|
|
|
|
- Data transfer on USB is packetized; each endpoint has a maximum
|
|
packet size. Drivers must often be aware of conventions such as
|
|
flagging the end of bulk transfers using "short" (including zero
|
|
length) packets.
|
|
|
|
- The Linux USB API supports synchronous calls for control and bulk
|
|
messages. It also supports asynchronous calls for all kinds of data
|
|
transfer, using request structures called "URBs" (USB Request
|
|
Blocks).
|
|
|
|
Accordingly, the USB Core API exposed to device drivers covers quite a
|
|
lot of territory. You'll probably need to consult the USB 3.0
|
|
specification, available online from www.usb.org at no cost, as well as
|
|
class or device specifications.
|
|
|
|
The only host-side drivers that actually touch hardware (reading/writing
|
|
registers, handling IRQs, and so on) are the HCDs. In theory, all HCDs
|
|
provide the same functionality through the same API. In practice, that's
|
|
becoming more true, but there are still differences
|
|
that crop up especially with fault handling on the less common controllers.
|
|
Different controllers don't
|
|
necessarily report the same aspects of failures, and recovery from
|
|
faults (including software-induced ones like unlinking an URB) isn't yet
|
|
fully consistent. Device driver authors should make a point of doing
|
|
disconnect testing (while the device is active) with each different host
|
|
controller driver, to make sure drivers don't have bugs of their own as
|
|
well as to make sure they aren't relying on some HCD-specific behavior.
|
|
|
|
USB-Standard Types
|
|
==================
|
|
|
|
In ``<linux/usb/ch9.h>`` you will find the USB data types defined in
|
|
chapter 9 of the USB specification. These data types are used throughout
|
|
USB, and in APIs including this host side API, gadget APIs, and usbfs.
|
|
|
|
.. kernel-doc:: include/linux/usb/ch9.h
|
|
:internal:
|
|
|
|
Host-Side Data Types and Macros
|
|
===============================
|
|
|
|
The host side API exposes several layers to drivers, some of which are
|
|
more necessary than others. These support lifecycle models for host side
|
|
drivers and devices, and support passing buffers through usbcore to some
|
|
HCD that performs the I/O for the device driver.
|
|
|
|
.. kernel-doc:: include/linux/usb.h
|
|
:internal:
|
|
|
|
USB Core APIs
|
|
=============
|
|
|
|
There are two basic I/O models in the USB API. The most elemental one is
|
|
asynchronous: drivers submit requests in the form of an URB, and the
|
|
URB's completion callback handles the next step. All USB transfer types
|
|
support that model, although there are special cases for control URBs
|
|
(which always have setup and status stages, but may not have a data
|
|
stage) and isochronous URBs (which allow large packets and include
|
|
per-packet fault reports). Built on top of that is synchronous API
|
|
support, where a driver calls a routine that allocates one or more URBs,
|
|
submits them, and waits until they complete. There are synchronous
|
|
wrappers for single-buffer control and bulk transfers (which are awkward
|
|
to use in some driver disconnect scenarios), and for scatterlist based
|
|
streaming i/o (bulk or interrupt).
|
|
|
|
USB drivers need to provide buffers that can be used for DMA, although
|
|
they don't necessarily need to provide the DMA mapping themselves. There
|
|
are APIs to use used when allocating DMA buffers, which can prevent use
|
|
of bounce buffers on some systems. In some cases, drivers may be able to
|
|
rely on 64bit DMA to eliminate another kind of bounce buffer.
|
|
|
|
.. kernel-doc:: drivers/usb/core/urb.c
|
|
:export:
|
|
|
|
.. kernel-doc:: drivers/usb/core/message.c
|
|
:export:
|
|
|
|
.. kernel-doc:: drivers/usb/core/file.c
|
|
:export:
|
|
|
|
.. kernel-doc:: drivers/usb/core/driver.c
|
|
:export:
|
|
|
|
.. kernel-doc:: drivers/usb/core/usb.c
|
|
:export:
|
|
|
|
.. kernel-doc:: drivers/usb/core/hub.c
|
|
:export:
|
|
|
|
Host Controller APIs
|
|
====================
|
|
|
|
These APIs are only for use by host controller drivers, most of which
|
|
implement standard register interfaces such as XHCI, EHCI, OHCI, or UHCI. UHCI
|
|
was one of the first interfaces, designed by Intel and also used by VIA;
|
|
it doesn't do much in hardware. OHCI was designed later, to have the
|
|
hardware do more work (bigger transfers, tracking protocol state, and so
|
|
on). EHCI was designed with USB 2.0; its design has features that
|
|
resemble OHCI (hardware does much more work) as well as UHCI (some parts
|
|
of ISO support, TD list processing). XHCI was designed with USB 3.0. It
|
|
continues to shift support for functionality into hardware.
|
|
|
|
There are host controllers other than the "big three", although most PCI
|
|
based controllers (and a few non-PCI based ones) use one of those
|
|
interfaces. Not all host controllers use DMA; some use PIO, and there is
|
|
also a simulator and a virtual host controller to pipe USB over the network.
|
|
|
|
The same basic APIs are available to drivers for all those controllers.
|
|
For historical reasons they are in two layers: :c:type:`struct
|
|
usb_bus <usb_bus>` is a rather thin layer that became available
|
|
in the 2.2 kernels, while :c:type:`struct usb_hcd <usb_hcd>`
|
|
is a more featureful layer
|
|
that lets HCDs share common code, to shrink driver size and
|
|
significantly reduce hcd-specific behaviors.
|
|
|
|
.. kernel-doc:: drivers/usb/core/hcd.c
|
|
:export:
|
|
|
|
.. kernel-doc:: drivers/usb/core/hcd-pci.c
|
|
:export:
|
|
|
|
.. kernel-doc:: drivers/usb/core/buffer.c
|
|
:internal:
|
|
|
|
The USB Filesystem (usbfs)
|
|
==========================
|
|
|
|
This chapter presents the Linux *usbfs*. You may prefer to avoid writing
|
|
new kernel code for your USB driver; that's the problem that usbfs set
|
|
out to solve. User mode device drivers are usually packaged as
|
|
applications or libraries, and may use usbfs through some programming
|
|
library that wraps it. Such libraries include
|
|
`libusb <http://libusb.sourceforge.net>`__ for C/C++, and
|
|
`jUSB <http://jUSB.sourceforge.net>`__ for Java.
|
|
|
|
**Note**
|
|
|
|
This particular documentation is incomplete, especially with respect
|
|
to the asynchronous mode. As of kernel 2.5.66 the code and this
|
|
(new) documentation need to be cross-reviewed.
|
|
|
|
Configure usbfs into Linux kernels by enabling the *USB filesystem*
|
|
option (CONFIG_USB_DEVICEFS), and you get basic support for user mode
|
|
USB device drivers. Until relatively recently it was often (confusingly)
|
|
called *usbdevfs* although it wasn't solving what *devfs* was. Every USB
|
|
device will appear in usbfs, regardless of whether or not it has a
|
|
kernel driver.
|
|
|
|
What files are in "usbfs"?
|
|
--------------------------
|
|
|
|
Conventionally mounted at ``/proc/bus/usb``, usbfs features include:
|
|
|
|
- ``/proc/bus/usb/devices`` ... a text file showing each of the USB
|
|
devices on known to the kernel, and their configuration descriptors.
|
|
You can also poll() this to learn about new devices.
|
|
|
|
- ``/proc/bus/usb/BBB/DDD`` ... magic files exposing the each device's
|
|
configuration descriptors, and supporting a series of ioctls for
|
|
making device requests, including I/O to devices. (Purely for access
|
|
by programs.)
|
|
|
|
Each bus is given a number (BBB) based on when it was enumerated; within
|
|
each bus, each device is given a similar number (DDD). Those BBB/DDD
|
|
paths are not "stable" identifiers; expect them to change even if you
|
|
always leave the devices plugged in to the same hub port. *Don't even
|
|
think of saving these in application configuration files.* Stable
|
|
identifiers are available, for user mode applications that want to use
|
|
them. HID and networking devices expose these stable IDs, so that for
|
|
example you can be sure that you told the right UPS to power down its
|
|
second server. "usbfs" doesn't (yet) expose those IDs.
|
|
|
|
Mounting and Access Control
|
|
---------------------------
|
|
|
|
There are a number of mount options for usbfs, which will be of most
|
|
interest to you if you need to override the default access control
|
|
policy. That policy is that only root may read or write device files
|
|
(``/proc/bus/BBB/DDD``) although anyone may read the ``devices`` or
|
|
``drivers`` files. I/O requests to the device also need the
|
|
CAP_SYS_RAWIO capability,
|
|
|
|
The significance of that is that by default, all user mode device
|
|
drivers need super-user privileges. You can change modes or ownership in
|
|
a driver setup when the device hotplugs, or maye just start the driver
|
|
right then, as a privileged server (or some activity within one). That's
|
|
the most secure approach for multi-user systems, but for single user
|
|
systems ("trusted" by that user) it's more convenient just to grant
|
|
everyone all access (using the *devmode=0666* option) so the driver can
|
|
start whenever it's needed.
|
|
|
|
The mount options for usbfs, usable in /etc/fstab or in command line
|
|
invocations of *mount*, are:
|
|
|
|
*busgid*\ =NNNNN
|
|
Controls the GID used for the /proc/bus/usb/BBB directories.
|
|
(Default: 0)
|
|
|
|
*busmode*\ =MMM
|
|
Controls the file mode used for the /proc/bus/usb/BBB directories.
|
|
(Default: 0555)
|
|
|
|
*busuid*\ =NNNNN
|
|
Controls the UID used for the /proc/bus/usb/BBB directories.
|
|
(Default: 0)
|
|
|
|
*devgid*\ =NNNNN
|
|
Controls the GID used for the /proc/bus/usb/BBB/DDD files. (Default:
|
|
0)
|
|
|
|
*devmode*\ =MMM
|
|
Controls the file mode used for the /proc/bus/usb/BBB/DDD files.
|
|
(Default: 0644)
|
|
|
|
*devuid*\ =NNNNN
|
|
Controls the UID used for the /proc/bus/usb/BBB/DDD files. (Default:
|
|
0)
|
|
|
|
*listgid*\ =NNNNN
|
|
Controls the GID used for the /proc/bus/usb/devices and drivers
|
|
files. (Default: 0)
|
|
|
|
*listmode*\ =MMM
|
|
Controls the file mode used for the /proc/bus/usb/devices and
|
|
drivers files. (Default: 0444)
|
|
|
|
*listuid*\ =NNNNN
|
|
Controls the UID used for the /proc/bus/usb/devices and drivers
|
|
files. (Default: 0)
|
|
|
|
Note that many Linux distributions hard-wire the mount options for usbfs
|
|
in their init scripts, such as ``/etc/rc.d/rc.sysinit``, rather than
|
|
making it easy to set this per-system policy in ``/etc/fstab``.
|
|
|
|
/proc/bus/usb/devices
|
|
---------------------
|
|
|
|
This file is handy for status viewing tools in user mode, which can scan
|
|
the text format and ignore most of it. More detailed device status
|
|
(including class and vendor status) is available from device-specific
|
|
files. For information about the current format of this file, see the
|
|
``Documentation/usb/proc_usb_info.txt`` file in your Linux kernel
|
|
sources.
|
|
|
|
This file, in combination with the poll() system call, can also be used
|
|
to detect when devices are added or removed:
|
|
|
|
::
|
|
|
|
int fd;
|
|
struct pollfd pfd;
|
|
|
|
fd = open("/proc/bus/usb/devices", O_RDONLY);
|
|
pfd = { fd, POLLIN, 0 };
|
|
for (;;) {
|
|
/* The first time through, this call will return immediately. */
|
|
poll(&pfd, 1, -1);
|
|
|
|
/* To see what's changed, compare the file's previous and current
|
|
contents or scan the filesystem. (Scanning is more precise.) */
|
|
}
|
|
|
|
Note that this behavior is intended to be used for informational and
|
|
debug purposes. It would be more appropriate to use programs such as
|
|
udev or HAL to initialize a device or start a user-mode helper program,
|
|
for instance.
|
|
|
|
/proc/bus/usb/BBB/DDD
|
|
---------------------
|
|
|
|
Use these files in one of these basic ways:
|
|
|
|
*They can be read,* producing first the device descriptor (18 bytes) and
|
|
then the descriptors for the current configuration. See the USB 2.0 spec
|
|
for details about those binary data formats. You'll need to convert most
|
|
multibyte values from little endian format to your native host byte
|
|
order, although a few of the fields in the device descriptor (both of
|
|
the BCD-encoded fields, and the vendor and product IDs) will be
|
|
byteswapped for you. Note that configuration descriptors include
|
|
descriptors for interfaces, altsettings, endpoints, and maybe additional
|
|
class descriptors.
|
|
|
|
*Perform USB operations* using *ioctl()* requests to make endpoint I/O
|
|
requests (synchronously or asynchronously) or manage the device. These
|
|
requests need the CAP_SYS_RAWIO capability, as well as filesystem
|
|
access permissions. Only one ioctl request can be made on one of these
|
|
device files at a time. This means that if you are synchronously reading
|
|
an endpoint from one thread, you won't be able to write to a different
|
|
endpoint from another thread until the read completes. This works for
|
|
*half duplex* protocols, but otherwise you'd use asynchronous i/o
|
|
requests.
|
|
|
|
Life Cycle of User Mode Drivers
|
|
-------------------------------
|
|
|
|
Such a driver first needs to find a device file for a device it knows
|
|
how to handle. Maybe it was told about it because a ``/sbin/hotplug``
|
|
event handling agent chose that driver to handle the new device. Or
|
|
maybe it's an application that scans all the /proc/bus/usb device files,
|
|
and ignores most devices. In either case, it should :c:func:`read()`
|
|
all the descriptors from the device file, and check them against what it
|
|
knows how to handle. It might just reject everything except a particular
|
|
vendor and product ID, or need a more complex policy.
|
|
|
|
Never assume there will only be one such device on the system at a time!
|
|
If your code can't handle more than one device at a time, at least
|
|
detect when there's more than one, and have your users choose which
|
|
device to use.
|
|
|
|
Once your user mode driver knows what device to use, it interacts with
|
|
it in either of two styles. The simple style is to make only control
|
|
requests; some devices don't need more complex interactions than those.
|
|
(An example might be software using vendor-specific control requests for
|
|
some initialization or configuration tasks, with a kernel driver for the
|
|
rest.)
|
|
|
|
More likely, you need a more complex style driver: one using non-control
|
|
endpoints, reading or writing data and claiming exclusive use of an
|
|
interface. *Bulk* transfers are easiest to use, but only their sibling
|
|
*interrupt* transfers work with low speed devices. Both interrupt and
|
|
*isochronous* transfers offer service guarantees because their bandwidth
|
|
is reserved. Such "periodic" transfers are awkward to use through usbfs,
|
|
unless you're using the asynchronous calls. However, interrupt transfers
|
|
can also be used in a synchronous "one shot" style.
|
|
|
|
Your user-mode driver should never need to worry about cleaning up
|
|
request state when the device is disconnected, although it should close
|
|
its open file descriptors as soon as it starts seeing the ENODEV errors.
|
|
|
|
The ioctl() Requests
|
|
--------------------
|
|
|
|
To use these ioctls, you need to include the following headers in your
|
|
userspace program:
|
|
|
|
::
|
|
|
|
#include <linux/usb.h>
|
|
#include <linux/usbdevice_fs.h>
|
|
#include <asm/byteorder.h>
|
|
|
|
The standard USB device model requests, from "Chapter 9" of the USB 2.0
|
|
specification, are automatically included from the ``<linux/usb/ch9.h>``
|
|
header.
|
|
|
|
Unless noted otherwise, the ioctl requests described here will update
|
|
the modification time on the usbfs file to which they are applied
|
|
(unless they fail). A return of zero indicates success; otherwise, a
|
|
standard USB error code is returned. (These are documented in
|
|
``Documentation/usb/error-codes.txt`` in your kernel sources.)
|
|
|
|
Each of these files multiplexes access to several I/O streams, one per
|
|
endpoint. Each device has one control endpoint (endpoint zero) which
|
|
supports a limited RPC style RPC access. Devices are configured by
|
|
hub_wq (in the kernel) setting a device-wide *configuration* that
|
|
affects things like power consumption and basic functionality. The
|
|
endpoints are part of USB *interfaces*, which may have *altsettings*
|
|
affecting things like which endpoints are available. Many devices only
|
|
have a single configuration and interface, so drivers for them will
|
|
ignore configurations and altsettings.
|
|
|
|
Management/Status Requests
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
A number of usbfs requests don't deal very directly with device I/O.
|
|
They mostly relate to device management and status. These are all
|
|
synchronous requests.
|
|
|
|
USBDEVFS_CLAIMINTERFACE
|
|
This is used to force usbfs to claim a specific interface, which has
|
|
not previously been claimed by usbfs or any other kernel driver. The
|
|
ioctl parameter is an integer holding the number of the interface
|
|
(bInterfaceNumber from descriptor).
|
|
|
|
Note that if your driver doesn't claim an interface before trying to
|
|
use one of its endpoints, and no other driver has bound to it, then
|
|
the interface is automatically claimed by usbfs.
|
|
|
|
This claim will be released by a RELEASEINTERFACE ioctl, or by
|
|
closing the file descriptor. File modification time is not updated
|
|
by this request.
|
|
|
|
USBDEVFS_CONNECTINFO
|
|
Says whether the device is lowspeed. The ioctl parameter points to a
|
|
structure like this:
|
|
|
|
::
|
|
|
|
struct usbdevfs_connectinfo {
|
|
unsigned int devnum;
|
|
unsigned char slow;
|
|
};
|
|
|
|
File modification time is not updated by this request.
|
|
|
|
*You can't tell whether a "not slow" device is connected at high
|
|
speed (480 MBit/sec) or just full speed (12 MBit/sec).* You should
|
|
know the devnum value already, it's the DDD value of the device file
|
|
name.
|
|
|
|
USBDEVFS_GETDRIVER
|
|
Returns the name of the kernel driver bound to a given interface (a
|
|
string). Parameter is a pointer to this structure, which is
|
|
modified:
|
|
|
|
::
|
|
|
|
struct usbdevfs_getdriver {
|
|
unsigned int interface;
|
|
char driver[USBDEVFS_MAXDRIVERNAME + 1];
|
|
};
|
|
|
|
File modification time is not updated by this request.
|
|
|
|
USBDEVFS_IOCTL
|
|
Passes a request from userspace through to a kernel driver that has
|
|
an ioctl entry in the *struct usb_driver* it registered.
|
|
|
|
::
|
|
|
|
struct usbdevfs_ioctl {
|
|
int ifno;
|
|
int ioctl_code;
|
|
void *data;
|
|
};
|
|
|
|
/* user mode call looks like this.
|
|
* 'request' becomes the driver->ioctl() 'code' parameter.
|
|
* the size of 'param' is encoded in 'request', and that data
|
|
* is copied to or from the driver->ioctl() 'buf' parameter.
|
|
*/
|
|
static int
|
|
usbdev_ioctl (int fd, int ifno, unsigned request, void *param)
|
|
{
|
|
struct usbdevfs_ioctl wrapper;
|
|
|
|
wrapper.ifno = ifno;
|
|
wrapper.ioctl_code = request;
|
|
wrapper.data = param;
|
|
|
|
return ioctl (fd, USBDEVFS_IOCTL, &wrapper);
|
|
}
|
|
|
|
File modification time is not updated by this request.
|
|
|
|
This request lets kernel drivers talk to user mode code through
|
|
filesystem operations even when they don't create a character or
|
|
block special device. It's also been used to do things like ask
|
|
devices what device special file should be used. Two pre-defined
|
|
ioctls are used to disconnect and reconnect kernel drivers, so that
|
|
user mode code can completely manage binding and configuration of
|
|
devices.
|
|
|
|
USBDEVFS_RELEASEINTERFACE
|
|
This is used to release the claim usbfs made on interface, either
|
|
implicitly or because of a USBDEVFS_CLAIMINTERFACE call, before the
|
|
file descriptor is closed. The ioctl parameter is an integer holding
|
|
the number of the interface (bInterfaceNumber from descriptor); File
|
|
modification time is not updated by this request.
|
|
|
|
**Warning**
|
|
|
|
*No security check is made to ensure that the task which made
|
|
the claim is the one which is releasing it. This means that user
|
|
mode driver may interfere other ones.*
|
|
|
|
USBDEVFS_RESETEP
|
|
Resets the data toggle value for an endpoint (bulk or interrupt) to
|
|
DATA0. The ioctl parameter is an integer endpoint number (1 to 15,
|
|
as identified in the endpoint descriptor), with USB_DIR_IN added
|
|
if the device's endpoint sends data to the host.
|
|
|
|
**Warning**
|
|
|
|
*Avoid using this request. It should probably be removed.* Using
|
|
it typically means the device and driver will lose toggle
|
|
synchronization. If you really lost synchronization, you likely
|
|
need to completely handshake with the device, using a request
|
|
like CLEAR_HALT or SET_INTERFACE.
|
|
|
|
USBDEVFS_DROP_PRIVILEGES
|
|
This is used to relinquish the ability to do certain operations
|
|
which are considered to be privileged on a usbfs file descriptor.
|
|
This includes claiming arbitrary interfaces, resetting a device on
|
|
which there are currently claimed interfaces from other users, and
|
|
issuing USBDEVFS_IOCTL calls. The ioctl parameter is a 32 bit mask
|
|
of interfaces the user is allowed to claim on this file descriptor.
|
|
You may issue this ioctl more than one time to narrow said mask.
|
|
|
|
Synchronous I/O Support
|
|
~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Synchronous requests involve the kernel blocking until the user mode
|
|
request completes, either by finishing successfully or by reporting an
|
|
error. In most cases this is the simplest way to use usbfs, although as
|
|
noted above it does prevent performing I/O to more than one endpoint at
|
|
a time.
|
|
|
|
USBDEVFS_BULK
|
|
Issues a bulk read or write request to the device. The ioctl
|
|
parameter is a pointer to this structure:
|
|
|
|
::
|
|
|
|
struct usbdevfs_bulktransfer {
|
|
unsigned int ep;
|
|
unsigned int len;
|
|
unsigned int timeout; /* in milliseconds */
|
|
void *data;
|
|
};
|
|
|
|
The "ep" value identifies a bulk endpoint number (1 to 15, as
|
|
identified in an endpoint descriptor), masked with USB_DIR_IN when
|
|
referring to an endpoint which sends data to the host from the
|
|
device. The length of the data buffer is identified by "len"; Recent
|
|
kernels support requests up to about 128KBytes. *FIXME say how read
|
|
length is returned, and how short reads are handled.*.
|
|
|
|
USBDEVFS_CLEAR_HALT
|
|
Clears endpoint halt (stall) and resets the endpoint toggle. This is
|
|
only meaningful for bulk or interrupt endpoints. The ioctl parameter
|
|
is an integer endpoint number (1 to 15, as identified in an endpoint
|
|
descriptor), masked with USB_DIR_IN when referring to an endpoint
|
|
which sends data to the host from the device.
|
|
|
|
Use this on bulk or interrupt endpoints which have stalled,
|
|
returning *-EPIPE* status to a data transfer request. Do not issue
|
|
the control request directly, since that could invalidate the host's
|
|
record of the data toggle.
|
|
|
|
USBDEVFS_CONTROL
|
|
Issues a control request to the device. The ioctl parameter points
|
|
to a structure like this:
|
|
|
|
::
|
|
|
|
struct usbdevfs_ctrltransfer {
|
|
__u8 bRequestType;
|
|
__u8 bRequest;
|
|
__u16 wValue;
|
|
__u16 wIndex;
|
|
__u16 wLength;
|
|
__u32 timeout; /* in milliseconds */
|
|
void *data;
|
|
};
|
|
|
|
The first eight bytes of this structure are the contents of the
|
|
SETUP packet to be sent to the device; see the USB 2.0 specification
|
|
for details. The bRequestType value is composed by combining a
|
|
USB_TYPE_\* value, a USB_DIR_\* value, and a USB_RECIP_\*
|
|
value (from *<linux/usb.h>*). If wLength is nonzero, it describes
|
|
the length of the data buffer, which is either written to the device
|
|
(USB_DIR_OUT) or read from the device (USB_DIR_IN).
|
|
|
|
At this writing, you can't transfer more than 4 KBytes of data to or
|
|
from a device; usbfs has a limit, and some host controller drivers
|
|
have a limit. (That's not usually a problem.) *Also* there's no way
|
|
to say it's not OK to get a short read back from the device.
|
|
|
|
USBDEVFS_RESET
|
|
Does a USB level device reset. The ioctl parameter is ignored. After
|
|
the reset, this rebinds all device interfaces. File modification
|
|
time is not updated by this request.
|
|
|
|
**Warning**
|
|
|
|
*Avoid using this call* until some usbcore bugs get fixed, since
|
|
it does not fully synchronize device, interface, and driver (not
|
|
just usbfs) state.
|
|
|
|
USBDEVFS_SETINTERFACE
|
|
Sets the alternate setting for an interface. The ioctl parameter is
|
|
a pointer to a structure like this:
|
|
|
|
::
|
|
|
|
struct usbdevfs_setinterface {
|
|
unsigned int interface;
|
|
unsigned int altsetting;
|
|
};
|
|
|
|
File modification time is not updated by this request.
|
|
|
|
Those struct members are from some interface descriptor applying to
|
|
the current configuration. The interface number is the
|
|
bInterfaceNumber value, and the altsetting number is the
|
|
bAlternateSetting value. (This resets each endpoint in the
|
|
interface.)
|
|
|
|
USBDEVFS_SETCONFIGURATION
|
|
Issues the :c:func:`usb_set_configuration()` call for the
|
|
device. The parameter is an integer holding the number of a
|
|
configuration (bConfigurationValue from descriptor). File
|
|
modification time is not updated by this request.
|
|
|
|
**Warning**
|
|
|
|
*Avoid using this call* until some usbcore bugs get fixed, since
|
|
it does not fully synchronize device, interface, and driver (not
|
|
just usbfs) state.
|
|
|
|
Asynchronous I/O Support
|
|
~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
As mentioned above, there are situations where it may be important to
|
|
initiate concurrent operations from user mode code. This is particularly
|
|
important for periodic transfers (interrupt and isochronous), but it can
|
|
be used for other kinds of USB requests too. In such cases, the
|
|
asynchronous requests described here are essential. Rather than
|
|
submitting one request and having the kernel block until it completes,
|
|
the blocking is separate.
|
|
|
|
These requests are packaged into a structure that resembles the URB used
|
|
by kernel device drivers. (No POSIX Async I/O support here, sorry.) It
|
|
identifies the endpoint type (USBDEVFS_URB_TYPE_\*), endpoint
|
|
(number, masked with USB_DIR_IN as appropriate), buffer and length,
|
|
and a user "context" value serving to uniquely identify each request.
|
|
(It's usually a pointer to per-request data.) Flags can modify requests
|
|
(not as many as supported for kernel drivers).
|
|
|
|
Each request can specify a realtime signal number (between SIGRTMIN and
|
|
SIGRTMAX, inclusive) to request a signal be sent when the request
|
|
completes.
|
|
|
|
When usbfs returns these urbs, the status value is updated, and the
|
|
buffer may have been modified. Except for isochronous transfers, the
|
|
actual_length is updated to say how many bytes were transferred; if the
|
|
USBDEVFS_URB_DISABLE_SPD flag is set ("short packets are not OK"), if
|
|
fewer bytes were read than were requested then you get an error report.
|
|
|
|
::
|
|
|
|
struct usbdevfs_iso_packet_desc {
|
|
unsigned int length;
|
|
unsigned int actual_length;
|
|
unsigned int status;
|
|
};
|
|
|
|
struct usbdevfs_urb {
|
|
unsigned char type;
|
|
unsigned char endpoint;
|
|
int status;
|
|
unsigned int flags;
|
|
void *buffer;
|
|
int buffer_length;
|
|
int actual_length;
|
|
int start_frame;
|
|
int number_of_packets;
|
|
int error_count;
|
|
unsigned int signr;
|
|
void *usercontext;
|
|
struct usbdevfs_iso_packet_desc iso_frame_desc[];
|
|
};
|
|
|
|
For these asynchronous requests, the file modification time reflects
|
|
when the request was initiated. This contrasts with their use with the
|
|
synchronous requests, where it reflects when requests complete.
|
|
|
|
USBDEVFS_DISCARDURB
|
|
*TBS* File modification time is not updated by this request.
|
|
|
|
USBDEVFS_DISCSIGNAL
|
|
*TBS* File modification time is not updated by this request.
|
|
|
|
USBDEVFS_REAPURB
|
|
*TBS* File modification time is not updated by this request.
|
|
|
|
USBDEVFS_REAPURBNDELAY
|
|
*TBS* File modification time is not updated by this request.
|
|
|
|
USBDEVFS_SUBMITURB
|
|
*TBS*
|