This documentation is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA For more details see the file COPYING in the source distribution of 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 at the root (the system's master), hubs as interior nodes, and peripheral devices as leaves (and slaves). Modern PCs support several such trees of USB devices, usually one USB 2.0 tree (480 Mbit/sec each) with a few USB 1.1 trees (12 Mbit/sec each) that are used when you connect a USB 1.1 device directly to the machine's "root hub". That master/slave asymmetry was designed in part for ease of use. It is not physically possible to assemble (legal) USB cables incorrectly: all upstream "to-the-host" connectors are the rectangular type, matching the sockets on root hubs, and the downstream type are the squarish type (or they are built in to the peripheral). Software doesn't need to deal with distributed autoconfiguration since the pre-designated master node manages all that. At the electrical level, bus protocol overhead is reduced by eliminating arbitration and moving scheduling into host software. USB 1.0 was announced in January 1996, and was revised as USB 1.1 (with improvements in hub specification and support for interrupt-out transfers) in September 1998. USB 2.0 was released in April 2000, including high speed transfers and transaction translating hubs (used for USB 1.1 and 1.0 backward compatibility). USB support was added to Linux early in the 2.2 kernel series shortly before the 2.3 development forked off. Updates from 2.3 were regularly folded back into 2.2 releases, bringing new features such as /sbin/hotplug support, more drivers, and more robustness. The 2.5 kernel series continued such improvements, and also worked on USB 2.0 support, higher performance, better consistency between host controller drivers, API simplification (to make bugs less likely), and providing internal "kerneldoc" documentation. Linux can run inside USB devices as well as on the hosts that control the devices. Because the Linux 2.x USB support evolved to support mass market platforms such as Apple Macintosh or PC-compatible systems, it didn't address design concerns for those types of USB systems. So it can't be used inside mass-market PDAs, or other peripherals. USB device drivers running inside those Linux peripherals don't do the same things as the ones running inside hosts, and so they've been given a different name: they're called gadget drivers. This document does not present gadget drivers. Within the kernel, host-side drivers for USB devices talk to the "usbcore" APIs. There are two types of public "usbcore" APIs, targetted at two different layers of USB driver. Those are general purpose drivers, exposed through driver frameworks such as block, character, or network devices; and drivers that are part of the core, which are involved in managing a USB bus. Such core drivers include the hub driver, which manages trees of USB devices, and several different kinds of host controller driver (HCD), which control individual busses. The device model seen by USB drivers is relatively complex. USB supports four kinds of data transfer (control, bulk, interrupt, and isochronous). Two transfer types use bandwidth as it's available (control and bulk), while the other two types of transfer (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 that are capable of high speed operation must also support full speed configurations, along with a way to ask about the "other speed" configurations that might be used. Configurations have one or more "interface", 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 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 messaging. It also supports asynchnous 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 2.0 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 on the 2.5 kernels, but there are still differences that crop up especially with fault handling. 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. (You will need external USB 1.1 and/or USB 2.0 hubs to perform all those tests.) 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 Hackers Manual November 2007 struct usb_ctrlrequest 9 struct usb_ctrlrequest SETUP data for a USB device control request struct usb_ctrlrequest { __u8 bRequestType; __u8 bRequest; __le16 wValue; __le16 wIndex; __le16 wLength; }; bRequestType matches the USB bmRequestType field bRequest matches the USB bRequest field wValue matches the USB wValue field (le16 byte order) wIndex matches the USB wIndex field (le16 byte order) wLength matches the USB wLength field (le16 byte order) This structure is used to send control requests to a USB device. It matches the different fields of the USB 2.0 Spec section 9.3, table 9-2. See the USB spec for a fuller description of the different fields, and what they are used for. Note that the driver for any interface can issue control requests. For most devices, interfaces don't coordinate with each other, so such requests may be made at any time. 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 Hackers Manual November 2007 struct usb_host_endpoint 9 struct usb_host_endpoint host-side endpoint descriptor and queue struct usb_host_endpoint { struct usb_endpoint_descriptor desc; struct list_head urb_list; void * hcpriv; struct kobject * kobj; unsigned char * extra; int extralen; }; desc descriptor for this endpoint, wMaxPacketSize in native byteorder urb_list urbs queued to this endpoint; maintained by usbcore hcpriv for use by HCD; typically holds hardware dma queue head (QH) with one or more transfer descriptors (TDs) per urb kobj kobject for sysfs info extra descriptors following this endpoint in the configuration extralen how many bytes of extra are valid USB requests are always queued to a given endpoint, identified by a descriptor within an active interface in a given USB configuration. Kernel Hackers Manual November 2007 struct usb_interface 9 struct usb_interface what usb device drivers talk to struct usb_interface { struct usb_host_interface * altsetting; struct usb_host_interface * cur_altsetting; unsigned num_altsetting; int minor; enum usb_interface_condition condition; struct device dev; struct class_device * class_dev; }; altsetting array of interface structures, one for each alternate setting that may be selected. Each one includes a set of endpoint configurations. They will be in no particular order. cur_altsetting the current altsetting. num_altsetting number of altsettings defined. minor the minor number assigned to this interface, if this interface is bound to a driver that uses the USB major number. If this interface does not use the USB major, this field should be unused. The driver should set this value in the probe function of the driver, after it has been assigned a minor number from the USB core by calling usb_register_dev. condition binding state of the interface: not bound, binding (in probe), bound to a driver, or unbinding (in disconnect) dev driver model's view of this device class_dev driver model's class view of this device. USB device drivers attach to interfaces on a physical device. Each interface encapsulates a single high level function, such as feeding an audio stream to a speaker or reporting a change in a volume control. Many USB devices only have one interface. The protocol used to talk to an interface's endpoints can be defined in a usb class specification, or by a product's vendor. The (default) control endpoint is part of every interface, but is never listed among the interface's descriptors. The driver that is bound to the interface can use standard driver model calls such as dev_get_drvdata on the dev member of this structure. Each interface may have alternate settings. The initial configuration of a device sets altsetting 0, but the device driver can change that setting using usb_set_interface. Alternate settings are often used to control the the use of periodic endpoints, such as by having different endpoints use different amounts of reserved USB bandwidth. All standards-conformant USB devices that use isochronous endpoints will use them in non-default settings. The USB specification says that alternate setting numbers must run from 0 to one less than the total number of alternate settings. But some devices manage to mess this up, and the structures aren't necessarily stored in numerical order anyhow. Use usb_altnum_to_altsetting to look up an alternate setting in the altsetting array based on its number. Kernel Hackers Manual November 2007 struct usb_interface_cache 9 struct usb_interface_cache long-term representation of a device interface struct usb_interface_cache { unsigned num_altsetting; struct kref ref; struct usb_host_interface altsetting[0]; }; num_altsetting number of altsettings defined. ref reference counter. altsetting[0] variable-length array of interface structures, one for each alternate setting that may be selected. Each one includes a set of endpoint configurations. They will be in no particular order. These structures persist for the lifetime of a usb_device, unlike struct usb_interface (which persists only as long as its configuration is installed). The altsetting arrays can be accessed through these structures at any time, permitting comparison of configurations and providing support for the /proc/bus/usb/devices pseudo-file. Kernel Hackers Manual November 2007 struct usb_host_config 9 struct usb_host_config representation of a device's configuration struct usb_host_config { struct usb_config_descriptor desc; char * string; struct usb_interface * interface[USB_MAXINTERFACES]; struct usb_interface_cache * intf_cache[USB_MAXINTERFACES]; unsigned char * extra; int extralen; }; desc the device's configuration descriptor. string pointer to the cached version of the iConfiguration string, if present for this configuration. interface[USB_MAXINTERFACES] array of pointers to usb_interface structures, one for each interface in the configuration. The number of interfaces is stored in desc.bNumInterfaces. These pointers are valid only while the the configuration is active. intf_cache[USB_MAXINTERFACES] array of pointers to usb_interface_cache structures, one for each interface in the configuration. These structures exist for the entire life of the device. extra pointer to buffer containing all extra descriptors associated with this configuration (those preceding the first interface descriptor). extralen length of the extra descriptors buffer. USB devices may have multiple configurations, but only one can be active at any time. Each encapsulates a different operational environment; for example, a dual-speed device would have separate configurations for full-speed and high-speed operation. The number of configurations available is stored in the device descriptor as bNumConfigurations. A configuration can contain multiple interfaces. Each corresponds to a different function of the USB device, and all are available whenever the configuration is active. The USB standard says that interfaces are supposed to be numbered from 0 to desc.bNumInterfaces-1, but a lot of devices get this wrong. In addition, the interface array is not guaranteed to be sorted in numerical order. Use usb_ifnum_to_if to look up an interface entry based on its number. Device drivers should not attempt to activate configurations. The choice of which configuration to install is a policy decision based on such considerations as available power, functionality provided, and the user's desires (expressed through userspace tools). However, drivers can call usb_reset_configuration to reinitialize the current configuration and all its interfaces. Kernel Hackers Manual November 2007 usb_interface_claimed 9 usb_interface_claimed returns true iff an interface is claimed int usb_interface_claimed struct usb_interface * iface iface the interface being checked Returns true (nonzero) iff the interface is claimed, else false (zero). Callers must own the driver model's usb bus readlock. So driver probe entries don't need extra locking, but other call contexts may need to explicitly claim that lock. Kernel Hackers Manual November 2007 usb_make_path 9 usb_make_path returns stable device path in the usb tree int usb_make_path struct usb_device * dev char * buf size_t size dev the device whose path is being constructed buf where to put the string size how big is buf? Returns length of the string (> 0) or negative if size was too small. This identifier is intended to be stable, reflecting physical paths in hardware such as physical bus addresses for host controllers or ports on USB hubs. That makes it stay the same until systems are physically reconfigured, by re-cabling a tree of USB devices or by moving USB host controllers. Adding and removing devices, including virtual root hubs in host controller driver modules, does not change these path identifers; neither does rebooting or re-enumerating. These are more useful identifiers than changeable (unstable) ones like bus numbers or device addresses. With a partial exception for devices connected to USB 2.0 root hubs, these identifiers are also predictable. So long as the device tree isn't changed, plugging any USB device into a given hub port always gives it the same path. Because of the use of companion controllers, devices connected to ports on USB 2.0 root hubs (EHCI host controllers) will get one path ID if they are high speed, and a different one if they are full or low speed. Kernel Hackers Manual November 2007 USB_DEVICE 9 USB_DEVICE macro used to describe a specific usb device USB_DEVICE vend prod vend the 16 bit USB Vendor ID prod the 16 bit USB Product ID This macro is used to create a struct usb_device_id that matches a specific device. Kernel Hackers Manual November 2007 USB_DEVICE_VER 9 USB_DEVICE_VER macro used to describe a specific usb device with a USB_DEVICE_VER vend prod lo hi vend the 16 bit USB Vendor ID prod the 16 bit USB Product ID lo the bcdDevice_lo value hi the bcdDevice_hi value This macro is used to create a struct usb_device_id that matches a specific device, with a version range. This macro is used to create a struct usb_device_id that matches a specific device, with a version range. Kernel Hackers Manual November 2007 USB_DEVICE_INFO 9 USB_DEVICE_INFO macro used to describe a class of usb devices USB_DEVICE_INFO cl sc pr cl bDeviceClass value sc bDeviceSubClass value pr bDeviceProtocol value This macro is used to create a struct usb_device_id that matches a specific class of devices. Kernel Hackers Manual November 2007 USB_INTERFACE_INFO 9 USB_INTERFACE_INFO macro used to describe a class of usb interfaces USB_INTERFACE_INFO cl sc pr cl bInterfaceClass value sc bInterfaceSubClass value pr bInterfaceProtocol value This macro is used to create a struct usb_device_id that matches a specific class of interfaces. Kernel Hackers Manual November 2007 struct usb_driver 9 struct usb_driver identifies USB driver to usbcore struct usb_driver { const char * name; int (* probe) (struct usb_interface *intf,const struct usb_device_id *id); void (* disconnect) (struct usb_interface *intf); int (* ioctl) (struct usb_interface *intf, unsigned int code,void *buf); int (* suspend) (struct usb_interface *intf, pm_message_t message); int (* resume) (struct usb_interface *intf); const struct usb_device_id * id_table; struct usb_dynids dynids; struct device_driver driver; unsigned int no_dynamic_id:1; }; name The driver name should be unique among USB drivers, and should normally be the same as the module name. probe Called to see if the driver is willing to manage a particular interface on a device. If it is, probe returns zero and uses dev_set_drvdata to associate driver-specific data with the interface. It may also use usb_set_interface to specify the appropriate altsetting. If unwilling to manage the interface, return a negative errno value. disconnect Called when the interface is no longer accessible, usually because its device has been (or is being) disconnected or the driver module is being unloaded. ioctl Used for drivers that want to talk to userspace through the usbfs filesystem. This lets devices provide ways to expose information to user space regardless of where they do (or don't) show up otherwise in the filesystem. suspend Called when the device is going to be suspended by the system. resume Called when the device is being resumed by the system. id_table USB drivers use ID table to support hotplugging. Export this with MODULE_DEVICE_TABLE(usb,...). This must be set or your driver's probe function will never get called. dynids used internally to hold the list of dynamically added device ids for this driver. driver the driver model core driver structure. no_dynamic_id if set to 1, the USB core will not allow dynamic ids to be added to this driver by preventing the sysfs file from being created. USB drivers must provide a name, probe and disconnect methods, and an id_table. Other driver fields are optional. The id_table is used in hotplugging. It holds a set of descriptors, and specialized data may be associated with each entry. That table is used by both user and kernel mode hotplugging support. The probe and disconnect methods are called in a context where they can sleep, but they should avoid abusing the privilege. Most work to connect to a device should be done when the device is opened, and undone at the last close. The disconnect code needs to address concurrency issues with respect to open and close methods, as well as forcing all pending I/O requests to complete (by unlinking them as necessary, and blocking until the unlinks complete). Kernel Hackers Manual November 2007 struct usb_class_driver 9 struct usb_class_driver identifies a USB driver that wants to use the USB major number struct usb_class_driver { char * name; const struct file_operations * fops; int minor_base; }; name the usb class device name for this driver. Will show up in sysfs. fops pointer to the struct file_operations of this driver. minor_base the start of the minor range for this driver. This structure is used for the usb_register_dev and usb_unregister_dev functions, to consolidate a number of the parameters used for them. Kernel Hackers Manual November 2007 struct urb 9 struct urb USB Request Block struct urb { struct list_head urb_list; struct usb_device * dev; unsigned int pipe; int status; unsigned int transfer_flags; void * transfer_buffer; dma_addr_t transfer_dma; int transfer_buffer_length; int actual_length; unsigned char * setup_packet; dma_addr_t setup_dma; int start_frame; int number_of_packets; int interval; int error_count; void * context; usb_complete_t complete; struct usb_iso_packet_descriptor iso_frame_desc[0]; }; urb_list For use by current owner of the URB. dev Identifies the USB device to perform the request. pipe Holds endpoint number, direction, type, and more. Create these values with the eight macros available; usb_{snd,rcv}TYPEpipe(dev,endpoint), where the TYPE is ctrl (control), bulk, int (interrupt), or iso (isochronous). For example usb_sndbulkpipe or usb_rcvintpipe. Endpoint numbers range from zero to fifteen. Note that in endpoint two is a different endpoint (and pipe) from out endpoint two. The current configuration controls the existence, type, and maximum packet size of any given endpoint. status This is read in non-iso completion functions to get the status of the particular request. ISO requests only use it to tell whether the URB was unlinked; detailed status for each frame is in the fields of the iso_frame-desc. transfer_flags A variety of flags may be used to affect how URB submission, unlinking, or operation are handled. Different kinds of URB can use different flags. transfer_buffer This identifies the buffer to (or from) which the I/O request will be performed (unless URB_NO_TRANSFER_DMA_MAP is set). This buffer must be suitable for DMA; allocate it with kmalloc or equivalent. For transfers to in endpoints, contents of this buffer will be modified. This buffer is used for the data stage of control transfers. transfer_dma When transfer_flags includes URB_NO_TRANSFER_DMA_MAP, the device driver is saying that it provided this DMA address, which the host controller driver should use in preference to the transfer_buffer. transfer_buffer_length How big is transfer_buffer. The transfer may be broken up into chunks according to the current maximum packet size for the endpoint, which is a function of the configuration and is encoded in the pipe. When the length is zero, neither transfer_buffer nor transfer_dma is used. actual_length This is read in non-iso completion functions, and it tells how many bytes (out of transfer_buffer_length) were transferred. It will normally be the same as requested, unless either an error was reported or a short read was performed. The URB_SHORT_NOT_OK transfer flag may be used to make such short reads be reported as errors. setup_packet Only used for control transfers, this points to eight bytes of setup data. Control transfers always start by sending this data to the device. Then transfer_buffer is read or written, if needed. setup_dma For control transfers with URB_NO_SETUP_DMA_MAP set, the device driver has provided this DMA address for the setup packet. The host controller driver should use this in preference to setup_packet. start_frame Returns the initial frame for isochronous transfers. number_of_packets Lists the number of ISO transfer buffers. interval Specifies the polling interval for interrupt or isochronous transfers. The units are frames (milliseconds) for for full and low speed devices, and microframes (1/8 millisecond) for highspeed ones. error_count Returns the number of ISO transfers that reported errors. context For use in completion functions. This normally points to request-specific driver context. complete Completion handler. This URB is passed as the parameter to the completion function. The completion function may then do what it likes with the URB, including resubmitting or freeing it. iso_frame_desc[0] Used to provide arrays of ISO transfer buffers and to collect the transfer status for each buffer. This structure identifies USB transfer requests. URBs must be allocated by calling usb_alloc_urb and freed with a call to usb_free_urb. Initialization may be done using various usb_fill_*_urb functions. URBs are submitted using usb_submit_urb, and pending requests may be canceled using usb_unlink_urb or usb_kill_urb. Normally drivers provide I/O buffers allocated with kmalloc or otherwise taken from the general page pool. That is provided by transfer_buffer (control requests also use setup_packet), and host controller drivers perform a dma mapping (and unmapping) for each buffer transferred. Those mapping operations can be expensive on some platforms (perhaps using a dma bounce buffer or talking to an IOMMU), although they're cheap on commodity x86 and ppc hardware. Alternatively, drivers may pass the URB_NO_xxx_DMA_MAP transfer flags, which tell the host controller driver that no such mapping is needed since the device driver is DMA-aware. For example, a device driver might allocate a DMA buffer with usb_buffer_alloc or call usb_buffer_map. When these transfer flags are provided, host controller drivers will attempt to use the dma addresses found in the transfer_dma and/or setup_dma fields rather than determining a dma address themselves. (Note that transfer_buffer and setup_packet must still be set because not all host controllers use DMA, nor do virtual root hubs). All URBs submitted must initialize the dev, pipe, transfer_flags (may be zero), and complete fields. All URBs must also initialize transfer_buffer and transfer_buffer_length. They may provide the URB_SHORT_NOT_OK transfer flag, indicating that short reads are to be treated as errors; that flag is invalid for write requests. Bulk URBs may use the URB_ZERO_PACKET transfer flag, indicating that bulk OUT transfers should always terminate with a short packet, even if it means adding an extra zero length packet. Control URBs must provide a setup_packet. The setup_packet and transfer_buffer may each be mapped for DMA or not, independently of the other. The transfer_flags bits URB_NO_TRANSFER_DMA_MAP and URB_NO_SETUP_DMA_MAP indicate which buffers have already been mapped. URB_NO_SETUP_DMA_MAP is ignored for non-control URBs. Interrupt URBs must provide an interval, saying how often (in milliseconds or, for highspeed devices, 125 microsecond units) to poll for transfers. After the URB has been submitted, the interval field reflects how the transfer was actually scheduled. The polling interval may be more frequent than requested. For example, some controllers have a maximum interval of 32 milliseconds, while others support intervals of up to 1024 milliseconds. Isochronous URBs also have transfer intervals. (Note that for isochronous endpoints, as well as high speed interrupt endpoints, the encoding of the transfer interval in the endpoint descriptor is logarithmic. Device drivers must convert that value to linear units themselves.) Isochronous URBs normally use the URB_ISO_ASAP transfer flag, telling the host controller to schedule the transfer as soon as bandwidth utilization allows, and then set start_frame to reflect the actual frame selected during submission. Otherwise drivers must specify the start_frame and handle the case where the transfer can't begin then. However, drivers won't know how bandwidth is currently allocated, and while they can find the current frame using usb_get_current_frame_number () they can't know the range for that frame number. (Ranges for frame counter values are HC-specific, and can go from 256 to 65536 frames from now.) Isochronous URBs have a different data transfer model, in part because the quality of service is only best effort. Callers provide specially allocated URBs, with number_of_packets worth of iso_frame_desc structures at the end. Each such packet is an individual ISO transfer. Isochronous URBs are normally queued, submitted by drivers to arrange that transfers are at least double buffered, and then explicitly resubmitted in completion handlers, so that data (such as audio or video) streams at as constant a rate as the host controller scheduler can support. The completion callback is made in_interrupt, and one of the first things that a completion handler should do is check the status field. The status field is provided for all URBs. It is used to report unlinked URBs, and status for all non-ISO transfers. It should not be examined before the URB is returned to the completion handler. The context field is normally used to link URBs back to the relevant driver or request state. When the completion callback is invoked for non-isochronous URBs, the actual_length field tells how many bytes were transferred. This field is updated even when the URB terminated with an error or was unlinked. ISO transfer status is reported in the status and actual_length fields of the iso_frame_desc array, and the number of errors is reported in error_count. Completion callbacks for ISO transfers will normally (re)submit URBs to ensure a constant transfer rate. Note that even fields marked public should not be touched by the driver when the urb is owned by the hcd, that is, since the call to usb_submit_urb till the entry into the completion routine. Kernel Hackers Manual November 2007 usb_fill_control_urb 9 usb_fill_control_urb initializes a control urb void usb_fill_control_urb struct urb * urb struct usb_device * dev unsigned int pipe unsigned char * setup_packet void * transfer_buffer int buffer_length usb_complete_t complete void * context urb pointer to the urb to initialize. dev pointer to the struct usb_device for this urb. pipe the endpoint pipe setup_packet pointer to the setup_packet buffer transfer_buffer pointer to the transfer buffer buffer_length length of the transfer buffer complete pointer to the usb_complete_t function context what to set the urb context to. Initializes a control urb with the proper information needed to submit it to a device. Kernel Hackers Manual November 2007 usb_fill_bulk_urb 9 usb_fill_bulk_urb macro to help initialize a bulk urb void usb_fill_bulk_urb struct urb * urb struct usb_device * dev unsigned int pipe void * transfer_buffer int buffer_length usb_complete_t complete void * context urb pointer to the urb to initialize. dev pointer to the struct usb_device for this urb. pipe the endpoint pipe transfer_buffer pointer to the transfer buffer buffer_length length of the transfer buffer complete pointer to the usb_complete_t function context what to set the urb context to. Initializes a bulk urb with the proper information needed to submit it to a device. Kernel Hackers Manual November 2007 usb_fill_int_urb 9 usb_fill_int_urb macro to help initialize a interrupt urb void usb_fill_int_urb struct urb * urb struct usb_device * dev unsigned int pipe void * transfer_buffer int buffer_length usb_complete_t complete void * context int interval urb pointer to the urb to initialize. dev pointer to the struct usb_device for this urb. pipe the endpoint pipe transfer_buffer pointer to the transfer buffer buffer_length length of the transfer buffer complete pointer to the usb_complete_t function context what to set the urb context to. interval what to set the urb interval to, encoded like the endpoint descriptor's bInterval value. Initializes a interrupt urb with the proper information needed to submit it to a device. Note that high speed interrupt endpoints use a logarithmic encoding of the endpoint interval, and express polling intervals in microframes (eight per millisecond) rather than in frames (one per millisecond). Kernel Hackers Manual November 2007 struct usb_sg_request 9 struct usb_sg_request support for scatter/gather I/O struct usb_sg_request { int status; size_t bytes; }; status zero indicates success, else negative errno bytes counts bytes transferred. These requests are initialized using usb_sg_init, and then are used as request handles passed to usb_sg_wait or usb_sg_cancel. Most members of the request object aren't for driver access. The status and bytecount values are valid only after usb_sg_wait returns. If the status is zero, then the bytecount matches the total from the request. After an error completion, drivers may need to clear a halt condition on the endpoint. 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 handle 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 Hackers Manual November 2007 usb_init_urb 9 usb_init_urb initializes a urb so that it can be used by a USB driver void usb_init_urb struct urb * urb urb pointer to the urb to initialize Initializes a urb so that the USB subsystem can use it properly. If a urb is created with a call to usb_alloc_urb it is not necessary to call this function. Only use this if you allocate the space for a struct urb on your own. If you call this function, be careful when freeing the memory for your urb that it is no longer in use by the USB core. Only use this function if you _really_ understand what you are doing. Kernel Hackers Manual November 2007 usb_alloc_urb 9 usb_alloc_urb creates a new urb for a USB driver to use struct urb * usb_alloc_urb int iso_packets gfp_t mem_flags iso_packets number of iso packets for this urb mem_flags the type of memory to allocate, see kmalloc for a list of valid options for this. Creates an urb for the USB driver to use, initializes a few internal structures, incrementes the usage counter, and returns a pointer to it. If no memory is available, NULL is returned. If the driver want to use this urb for interrupt, control, or bulk endpoints, pass '0' as the number of iso packets. The driver must call usb_free_urb when it is finished with the urb. Kernel Hackers Manual November 2007 usb_free_urb 9 usb_free_urb frees the memory used by a urb when all users of it are finished void usb_free_urb struct urb * urb urb pointer to the urb to free, may be NULL Must be called when a user of a urb is finished with it. When the last user of the urb calls this function, the memory of the urb is freed. The transfer buffer associated with the urb is not freed, that must be done elsewhere. Kernel Hackers Manual November 2007 usb_get_urb 9 usb_get_urb increments the reference count of the urb struct urb * usb_get_urb struct urb * urb urb pointer to the urb to modify, may be NULL This must be called whenever a urb is transferred from a device driver to a host controller driver. This allows proper reference counting to happen for urbs. A pointer to the urb with the incremented reference counter is returned. Kernel Hackers Manual November 2007 usb_submit_urb 9 usb_submit_urb issue an asynchronous transfer request for an endpoint int usb_submit_urb struct urb * urb gfp_t mem_flags urb pointer to the urb describing the request mem_flags the type of memory to allocate, see kmalloc for a list of valid options for this. This submits a transfer request, and transfers control of the URB describing that request to the USB subsystem. Request completion will be indicated later, asynchronously, by calling the completion handler. The three types of completion are success, error, and unlink (a software-induced fault, also called request cancellation). URBs may be submitted in interrupt context. The caller must have correctly initialized the URB before submitting it. Functions such as usb_fill_bulk_urb and usb_fill_control_urb are available to ensure that most fields are correctly initialized, for the particular kind of transfer, although they will not initialize any transfer flags. Successful submissions return 0; otherwise this routine returns a negative error number. If the submission is successful, the complete callback from the URB will be called exactly once, when the USB core and Host Controller Driver (HCD) are finished with the URB. When the completion function is called, control of the URB is returned to the device driver which issued the request. The completion handler may then immediately free or reuse that URB. With few exceptions, USB device drivers should never access URB fields provided by usbcore or the HCD until its complete is called. The exceptions relate to periodic transfer scheduling. For both interrupt and isochronous urbs, as part of successful URB submission urb->interval is modified to reflect the actual transfer period used (normally some power of two units). And for isochronous urbs, urb->start_frame is modified to reflect when the URB's transfers were scheduled to start. Not all isochronous transfer scheduling policies will work, but most host controller drivers should easily handle ISO queues going from now until 10-200 msec into the future. For control endpoints, the synchronous usb_control_msg call is often used (in non-interrupt context) instead of this call. That is often used through convenience wrappers, for the requests that are standardized in the USB 2.0 specification. For bulk endpoints, a synchronous usb_bulk_msg call is available. URBs may be submitted to endpoints before previous ones complete, to minimize the impact of interrupt latencies and system overhead on data throughput. With that queuing policy, an endpoint's queue would never be empty. This is required for continuous isochronous data streams, and may also be required for some kinds of interrupt transfers. Such queuing also maximizes bandwidth utilization by letting USB controllers start work on later requests before driver software has finished the completion processing for earlier (successful) requests. As of Linux 2.6, all USB endpoint transfer queues support depths greater than one. This was previously a HCD-specific behavior, except for ISO transfers. Non-isochronous endpoint queues are inactive during cleanup after faults (transfer errors or cancellation). Periodic transfers (interrupt or isochronous) are performed repeatedly, using the interval specified in the urb. Submitting the first urb to the endpoint reserves the bandwidth necessary to make those transfers. If the USB subsystem can't allocate sufficient bandwidth to perform the periodic request, submitting such a periodic request should fail. Device drivers must explicitly request that repetition, by ensuring that some URB is always on the endpoint's queue (except possibly for short periods during completion callacks). When there is no longer an urb queued, the endpoint's bandwidth reservation is canceled. This means drivers can use their completion handlers to ensure they keep bandwidth they need, by reinitializing and resubmitting the just-completed urb until the driver longer needs that periodic bandwidth. The general rules for how to decide which mem_flags to use are the same as for kmalloc. There are four different possible values; GFP_KERNEL, GFP_NOFS, GFP_NOIO and GFP_ATOMIC. GFP_NOFS is not ever used, as it has not been implemented yet. GFP_ATOMIC is used when (a) you are inside a completion handler, an interrupt, bottom half, tasklet or timer, or (b) you are holding a spinlock or rwlock (does not apply to semaphores), or (c) current->state != TASK_RUNNING, this is the case only after you've changed it. GFP_NOIO is used in the block io path and error handling of storage devices. All other situations use GFP_KERNEL. Some more specific rules for mem_flags can be inferred, such as (1) start_xmit, timeout, and receive methods of network drivers must use GFP_ATOMIC (they are called with a spinlock held); (2) queuecommand methods of scsi drivers must use GFP_ATOMIC (also called with a spinlock held); (3) If you use a kernel thread with a network driver you must use GFP_NOIO, unless (b) or (c) apply; (4) after you have done a down you can use GFP_KERNEL, unless (b) or (c) apply or your are in a storage driver's block io path; (5) USB probe and disconnect can use GFP_KERNEL unless (b) or (c) apply; and (6) changing firmware on a running storage or net device uses GFP_NOIO, unless b) or c) apply Kernel Hackers Manual November 2007 usb_unlink_urb 9 usb_unlink_urb abort/cancel a transfer request for an endpoint int usb_unlink_urb struct urb * urb urb pointer to urb describing a previously submitted request, may be NULL This routine cancels an in-progress request. URBs complete only once per submission, and may be canceled only once per submission. Successful cancellation means the requests's completion handler will be called with a status code indicating that the request has been canceled (rather than any other code) and will quickly be removed from host controller data structures. This request is always asynchronous. Success is indicated by returning -EINPROGRESS, at which time the URB will normally have been unlinked but not yet given back to the device driver. When it is called, the completion function will see urb->status == -ECONNRESET. Failure is indicated by any other return value. Unlinking will fail when the URB is not currently linked (i.e., it was never submitted, or it was unlinked before, or the hardware is already finished with it), even if the completion handler has not yet run. Host Controller Drivers (HCDs) place all the URBs for a particular endpoint in a queue. Normally the queue advances as the controller hardware processes each request. But when an URB terminates with an error its queue stops, at least until that URB's completion routine returns. It is guaranteed that the queue will not restart until all its unlinked URBs have been fully retired, with their completion routines run, even if that's not until some time after the original completion handler returns. Normally the same behavior and guarantees apply when an URB terminates because it was unlinked; however if an URB is unlinked before the hardware has started to execute it, then its queue is not guaranteed to stop until all the preceding URBs have completed. This means that USB device drivers can safely build deep queues for large or complex transfers, and clean them up reliably after any sort of aborted transfer by unlinking all pending URBs at the first fault. Note that an URB terminating early because a short packet was received will count as an error if and only if the URB_SHORT_NOT_OK flag is set. Also, that all unlinks performed in any URB completion handler must be asynchronous. Queues for isochronous endpoints are treated differently, because they advance at fixed rates. Such queues do not stop when an URB is unlinked. An unlinked URB may leave a gap in the stream of packets. It is undefined whether such gaps can be filled in. When a control URB terminates with an error, it is likely that the status stage of the transfer will not take place, even if it is merely a soft error resulting from a short-packet with URB_SHORT_NOT_OK set. Kernel Hackers Manual November 2007 usb_kill_urb 9 usb_kill_urb cancel a transfer request and wait for it to finish void usb_kill_urb struct urb * urb urb pointer to URB describing a previously submitted request, may be NULL This routine cancels an in-progress request. It is guaranteed that upon return all completion handlers will have finished and the URB will be totally idle and available for reuse. These features make this an ideal way to stop I/O in a disconnect callback or close function. If the request has not already finished or been unlinked the completion handler will see urb->status == -ENOENT. While the routine is running, attempts to resubmit the URB will fail with error -EPERM. Thus even if the URB's completion handler always tries to resubmit, it will not succeed and the URB will become idle. This routine may not be used in an interrupt context (such as a bottom half or a completion handler), or when holding a spinlock, or in other situations where the caller can't schedule. Kernel Hackers Manual November 2007 usb_control_msg 9 usb_control_msg Builds a control urb, sends it off and waits for completion int usb_control_msg struct usb_device * dev unsigned int pipe __u8 request __u8 requesttype __u16 value __u16 index void * data __u16 size int timeout dev pointer to the usb device to send the message to pipe endpoint pipe to send the message to request USB message request value requesttype USB message request type value value USB message value index USB message index value data pointer to the data to send size length in bytes of the data to send timeout time in msecs to wait for the message to complete before timing out (if 0 the wait is forever) !in_interrupt () This function sends a simple control message to a specified endpoint and waits for the message to complete, or timeout. If successful, it returns the number of bytes transferred, otherwise a negative error number. Don't use this function from within an interrupt context, like a bottom half handler. If you need an asynchronous message, or need to send a message from within interrupt context, use usb_submit_urb If a thread in your driver uses this call, make sure your disconnect method can wait for it to complete. Since you don't have a handle on the URB used, you can't cancel the request. Kernel Hackers Manual November 2007 usb_bulk_msg 9 usb_bulk_msg Builds a bulk urb, sends it off and waits for completion int usb_bulk_msg struct usb_device * usb_dev unsigned int pipe void * data int len int * actual_length int timeout usb_dev pointer to the usb device to send the message to pipe endpoint pipe to send the message to data pointer to the data to send len length in bytes of the data to send actual_length pointer to a location to put the actual length transferred in bytes timeout time in msecs to wait for the message to complete before timing out (if 0 the wait is forever) !in_interrupt () This function sends a simple bulk message to a specified endpoint and waits for the message to complete, or timeout. If successful, it returns 0, otherwise a negative error number. The number of actual bytes transferred will be stored in the actual_length paramater. Don't use this function from within an interrupt context, like a bottom half handler. If you need an asynchronous message, or need to send a message from within interrupt context, use usb_submit_urb If a thread in your driver uses this call, make sure your disconnect method can wait for it to complete. Since you don't have a handle on the URB used, you can't cancel the request. Because there is no usb_interrupt_msg and no USBDEVFS_INTERRUPT ioctl, users are forced to abuse this routine by using it to submit URBs for interrupt endpoints. We will take the liberty of creating an interrupt URB (with the default interval) if the target is an interrupt endpoint. Kernel Hackers Manual November 2007 usb_sg_init 9 usb_sg_init initializes scatterlist-based bulk/interrupt I/O request int usb_sg_init struct usb_sg_request * io struct usb_device * dev unsigned pipe unsigned period struct scatterlist * sg int nents size_t length gfp_t mem_flags io request block being initialized. until usb_sg_wait returns, treat this as a pointer to an opaque block of memory, dev the usb device that will send or receive the data pipe endpoint pipe used to transfer the data period polling rate for interrupt endpoints, in frames or (for high speed endpoints) microframes; ignored for bulk sg scatterlist entries nents how many entries in the scatterlist length how many bytes to send from the scatterlist, or zero to send every byte identified in the list. mem_flags SLAB_* flags affecting memory allocations in this call Returns zero for success, else a negative errno value. This initializes a scatter/gather request, allocating resources such as I/O mappings and urb memory (except maybe memory used by USB controller drivers). The request must be issued using usb_sg_wait, which waits for the I/O to complete (or to be canceled) and then cleans up all resources allocated by usb_sg_init. The request may be canceled with usb_sg_cancel, either before or after usb_sg_wait is called. Kernel Hackers Manual November 2007 usb_sg_wait 9 usb_sg_wait synchronously execute scatter/gather request void usb_sg_wait struct usb_sg_request * io io request block handle, as initialized with usb_sg_init. some fields become accessible when this call returns. !in_interrupt () This function blocks until the specified I/O operation completes. It leverages the grouping of the related I/O requests to get good transfer rates, by queueing the requests. At higher speeds, such queuing can significantly improve USB throughput. There are three kinds of completion for this function. (1) success, where io->status is zero. The number of io->bytes transferred is as requested. (2) error, where io->status is a negative errno value. The number of io->bytes transferred before the error is usually less than requested, and can be nonzero. (3) cancellation, a type of error with status -ECONNRESET that is initiated by usb_sg_cancel. When this function returns, all memory allocated through usb_sg_init or this call will have been freed. The request block parameter may still be passed to usb_sg_cancel, or it may be freed. It could also be reinitialized and then reused. Bulk transfers are valid for full or high speed endpoints. The best full speed data rate is 19 packets of 64 bytes each per frame, or 1216 bytes per millisecond. The best high speed data rate is 13 packets of 512 bytes each per microframe, or 52 KBytes per millisecond. The reason to use interrupt transfers through this API would most likely be to reserve high speed bandwidth, where up to 24 KBytes per millisecond could be transferred. That capability is less useful for low or full speed interrupt endpoints, which allow at most one packet per millisecond, of at most 8 or 64 bytes (respectively). Kernel Hackers Manual November 2007 usb_sg_cancel 9 usb_sg_cancel stop scatter/gather i/o issued by usb_sg_wait void usb_sg_cancel struct usb_sg_request * io io request block, initialized with usb_sg_init This stops a request after it has been started by usb_sg_wait. It can also prevents one initialized by usb_sg_init from starting, so that call just frees resources allocated to the request. Kernel Hackers Manual November 2007 usb_get_descriptor 9 usb_get_descriptor issues a generic GET_DESCRIPTOR request int usb_get_descriptor struct usb_device * dev unsigned char type unsigned char index void * buf int size dev the device whose descriptor is being retrieved type the descriptor type (USB_DT_*) index the number of the descriptor buf where to put the descriptor size how big is buf? !in_interrupt () Gets a USB descriptor. Convenience functions exist to simplify getting some types of descriptors. Use usb_get_string or usb_string for USB_DT_STRING. Device (USB_DT_DEVICE) and configuration descriptors (USB_DT_CONFIG) are part of the device structure. In addition to a number of USB-standard descriptors, some devices also use class-specific or vendor-specific descriptors. This call is synchronous, and may not be used in an interrupt context. Returns the number of bytes received on success, or else the status code returned by the underlying usb_control_msg call. Kernel Hackers Manual November 2007 usb_string 9 usb_string returns ISO 8859-1 version of a string descriptor int usb_string struct usb_device * dev int index char * buf size_t size dev the device whose string descriptor is being retrieved index the number of the descriptor buf where to put the string size how big is buf? !in_interrupt () This converts the UTF-16LE encoded strings returned by devices, from usb_get_string_descriptor, to null-terminated ISO-8859-1 encoded ones that are more usable in most kernel contexts. Note that all characters in the chosen descriptor that can't be encoded using ISO-8859-1 are converted to the question mark (?) character, and this function chooses strings in the first language supported by the device. The ASCII (or, redundantly, US-ASCII) character set is the seven-bit subset of ISO 8859-1. ISO-8859-1 is the eight-bit subset of Unicode, and is appropriate for use many uses of English and several other Western European languages. (But it doesn't include the Euro symbol.) This call is synchronous, and may not be used in an interrupt context. Returns length of the string (>= 0) or usb_control_msg status (< 0). Kernel Hackers Manual November 2007 usb_get_status 9 usb_get_status issues a GET_STATUS call int usb_get_status struct usb_device * dev int type int target void * data dev the device whose status is being checked type USB_RECIP_*; for device, interface, or endpoint target zero (for device), else interface or endpoint number data pointer to two bytes of bitmap data !in_interrupt () Returns device, interface, or endpoint status. Normally only of interest to see if the device is self powered, or has enabled the remote wakeup facility; or whether a bulk or interrupt endpoint is halted (stalled). Bits in these status bitmaps are set using the SET_FEATURE request, and cleared using the CLEAR_FEATURE request. The usb_clear_halt function should be used to clear halt (stall) status. This call is synchronous, and may not be used in an interrupt context. Returns the number of bytes received on success, or else the status code returned by the underlying usb_control_msg call. Kernel Hackers Manual November 2007 usb_clear_halt 9 usb_clear_halt tells device to clear endpoint halt/stall condition int usb_clear_halt struct usb_device * dev int pipe dev device whose endpoint is halted pipe endpoint pipe being cleared !in_interrupt () This is used to clear halt conditions for bulk and interrupt endpoints, as reported by URB completion status. Endpoints that are halted are sometimes referred to as being stalled. Such endpoints are unable to transmit or receive data until the halt status is cleared. Any URBs queued for such an endpoint should normally be unlinked by the driver before clearing the halt condition, as described in sections 5.7.5 and 5.8.5 of the USB 2.0 spec. Note that control and isochronous endpoints don't halt, although control endpoints report protocol stall (for unsupported requests) using the same status code used to report a true stall. This call is synchronous, and may not be used in an interrupt context. Returns zero on success, or else the status code returned by the underlying usb_control_msg call. Kernel Hackers Manual November 2007 usb_set_interface 9 usb_set_interface Makes a particular alternate setting be current int usb_set_interface struct usb_device * dev int interface int alternate dev the device whose interface is being updated interface the interface being updated alternate the setting being chosen. !in_interrupt () This is used to enable data transfers on interfaces that may not be enabled by default. Not all devices support such configurability. Only the driver bound to an interface may change its setting. Within any given configuration, each interface may have several alternative settings. These are often used to control levels of bandwidth consumption. For example, the default setting for a high speed interrupt endpoint may not send more than 64 bytes per microframe, while interrupt transfers of up to 3KBytes per microframe are legal. Also, isochronous endpoints may never be part of an interface's default setting. To access such bandwidth, alternate interface settings must be made current. Note that in the Linux USB subsystem, bandwidth associated with an endpoint in a given alternate setting is not reserved until an URB is submitted that needs that bandwidth. Some other operating systems allocate bandwidth early, when a configuration is chosen. This call is synchronous, and may not be used in an interrupt context. Also, drivers must not change altsettings while urbs are scheduled for endpoints in that interface; all such urbs must first be completed (perhaps forced by unlinking). Returns zero on success, or else the status code returned by the underlying usb_control_msg call. Kernel Hackers Manual November 2007 usb_reset_configuration 9 usb_reset_configuration lightweight device reset int usb_reset_configuration struct usb_device * dev dev the device whose configuration is being reset This issues a standard SET_CONFIGURATION request to the device using the current configuration. The effect is to reset most USB-related state in the device, including interface altsettings (reset to zero), endpoint halts (cleared), and data toggle (only for bulk and interrupt endpoints). Other usbcore state is unchanged, including bindings of usb device drivers to interfaces. Because this affects multiple interfaces, avoid using this with composite (multi-interface) devices. Instead, the driver for each interface may use usb_set_interface on the interfaces it claims. Be careful though; some devices don't support the SET_INTERFACE request, and others won't reset all the interface state (notably data toggles). Resetting the whole configuration would affect other drivers' interfaces. The caller must own the device lock. Returns zero on success, else a negative error code. Kernel Hackers Manual November 2007 usb_register_dev 9 usb_register_dev register a USB device, and ask for a minor number int usb_register_dev struct usb_interface * intf struct usb_class_driver * class_driver intf pointer to the usb_interface that is being registered class_driver pointer to the usb_class_driver for this device This should be called by all USB drivers that use the USB major number. If CONFIG_USB_DYNAMIC_MINORS is enabled, the minor number will be dynamically allocated out of the list of available ones. If it is not enabled, the minor number will be based on the next available free minor, starting at the class_driver->minor_base. This function also creates a usb class device in the sysfs tree. usb_deregister_dev must be called when the driver is done with the minor numbers given out by this function. Returns -EINVAL if something bad happens with trying to register a device, and 0 on success. Kernel Hackers Manual November 2007 usb_deregister_dev 9 usb_deregister_dev deregister a USB device's dynamic minor. void usb_deregister_dev struct usb_interface * intf struct usb_class_driver * class_driver intf pointer to the usb_interface that is being deregistered class_driver pointer to the usb_class_driver for this device Used in conjunction with usb_register_dev. This function is called when the USB driver is finished with the minor numbers gotten from a call to usb_register_dev (usually when the device is disconnected from the system.) This function also removes the usb class device from the sysfs tree. This should be called by all drivers that use the USB major number. Kernel Hackers Manual November 2007 usb_match_id 9 usb_match_id find first usb_device_id matching device or interface const struct usb_device_id * usb_match_id struct usb_interface * interface const struct usb_device_id * id interface the interface of interest id array of usb_device_id structures, terminated by zero entry usb_match_id searches an array of usb_device_id's and returns the first one matching the device or interface, or null. This is used when binding (or rebinding) a driver to an interface. Most USB device drivers will use this indirectly, through the usb core, but some layered driver frameworks use it directly. These device tables are exported with MODULE_DEVICE_TABLE, through modutils, to support the driver loading functionality of USB hotplugging. The match_flags element in a usb_device_id controls which members are used. If the corresponding bit is set, the value in the device_id must match its corresponding member in the device or interface descriptor, or else the device_id does not match. driver_info is normally used only by device drivers, but you can create a wildcard matches anything usb_device_id as a driver's modules.usbmap entry if you provide an id with only a nonzero driver_info field. If you do this, the USB device driver's probe routine should use additional intelligence to decide whether to bind to the specified interface. The match algorithm is very simple, so that intelligence in driver selection must come from smart driver id records. Unless you have good reasons to use another selection policy, provide match elements only in related groups, and order match specifiers from specific to general. Use the macros provided for that purpose if you can. The most specific match specifiers use device descriptor data. These are commonly used with product-specific matches; the USB_DEVICE macro lets you provide vendor and product IDs, and you can also match against ranges of product revisions. These are widely used for devices with application or vendor specific bDeviceClass values. Matches based on device class/subclass/protocol specifications are slightly more general; use the USB_DEVICE_INFO macro, or its siblings. These are used with single-function devices where bDeviceClass doesn't specify that each interface has its own class. Matches based on interface class/subclass/protocol are the most general; they let drivers bind to any interface on a multiple-function device. Use the USB_INTERFACE_INFO macro, or its siblings, to match class-per-interface style devices (as recorded in bDeviceClass). Within those groups, remember that not all combinations are meaningful. For example, don't give a product version range without vendor and product IDs; or specify a protocol without its associated class and subclass. Kernel Hackers Manual November 2007 usb_register_driver 9 usb_register_driver register a USB driver int usb_register_driver struct usb_driver * new_driver struct module * owner new_driver USB operations for the driver owner module owner of this driver. Registers a USB driver with the USB core. The list of unattached interfaces will be rescanned whenever a new driver is added, allowing the new driver to attach to any recognized devices. Returns a negative error code on failure and 0 on success. if you want your driver to use the USB major number, you must call usb_register_dev to enable that functionality. This function no longer takes care of that. Kernel Hackers Manual November 2007 usb_deregister 9 usb_deregister unregister a USB driver void usb_deregister struct usb_driver * driver driver USB operations of the driver to unregister must be able to sleep Unlinks the specified driver from the internal USB driver list. If you called usb_register_dev, you still need to call usb_deregister_dev to clean up your driver's allocated minor numbers, this * call will no longer do it for you. Kernel Hackers Manual November 2007 usb_ifnum_to_if 9 usb_ifnum_to_if get the interface object with a given interface number struct usb_interface * usb_ifnum_to_if struct usb_device * dev unsigned ifnum dev the device whose current configuration is considered ifnum the desired interface This walks the device descriptor for the currently active configuration and returns a pointer to the interface with that particular interface number, or null. Note that configuration descriptors are not required to assign interface numbers sequentially, so that it would be incorrect to assume that the first interface in that descriptor corresponds to interface zero. This routine helps device drivers avoid such mistakes. However, you should make sure that you do the right thing with any alternate settings available for this interfaces. Don't call this function unless you are bound to one of the interfaces on this device or you have locked the device! Kernel Hackers Manual November 2007 usb_altnum_to_altsetting 9 usb_altnum_to_altsetting get the altsetting structure with a given struct usb_host_interface * usb_altnum_to_altsetting struct usb_interface * intf unsigned int altnum intf the interface containing the altsetting in question altnum the desired alternate setting number This searches the altsetting array of the specified interface for an entry with the correct bAlternateSetting value and returns a pointer to that entry, or null. Note that altsettings need not be stored sequentially by number, so it would be incorrect to assume that the first altsetting entry in the array corresponds to altsetting zero. This routine helps device drivers avoid such mistakes. Don't call this function unless you are bound to the intf interface or you have locked the device! This searches the altsetting array of the specified interface for an entry with the correct bAlternateSetting value and returns a pointer to that entry, or null. Note that altsettings need not be stored sequentially by number, so it would be incorrect to assume that the first altsetting entry in the array corresponds to altsetting zero. This routine helps device drivers avoid such mistakes. Don't call this function unless you are bound to the intf interface or you have locked the device! Kernel Hackers Manual November 2007 usb_driver_claim_interface 9 usb_driver_claim_interface bind a driver to an interface int usb_driver_claim_interface struct usb_driver * driver struct usb_interface * iface void * priv driver the driver to be bound iface the interface to which it will be bound; must be in the usb device's active configuration priv driver data associated with that interface This is used by usb device drivers that need to claim more than one