usb_set_interface(9) [suse man page]
USB_SET_INTERFACE(9) USB Core APIs USB_SET_INTERFACE(9) NAME
usb_set_interface - Makes a particular alternate setting be current SYNOPSIS
int usb_set_interface(struct usb_device * dev, int interface, int alternate); ARGUMENTS
dev the device whose interface is being updated interface the interface being updated alternate the setting being chosen. CONTEXT
!in_interrupt () DESCRIPTION
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. COPYRIGHT
Kernel Hackers Manual 2.6. July 2010 USB_SET_INTERFACE(9)
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STRUCT
USB_INTERFACE(9) Host-Side Data Types and Macro STRUCT USB_INTERFACE(9) NAME
struct_usb_interface - what usb device drivers talk to SYNOPSIS
struct usb_interface { struct usb_host_interface * altsetting; struct usb_host_interface * cur_altsetting; unsigned num_altsetting; struct usb_interface_assoc_descriptor * intf_assoc; int minor; enum usb_interface_condition condition; unsigned sysfs_files_created:1; unsigned ep_devs_created:1; unsigned unregistering:1; unsigned needs_remote_wakeup:1; unsigned needs_altsetting0:1; unsigned needs_binding:1; unsigned reset_running:1; struct device dev; struct device * usb_dev; atomic_t pm_usage_cnt; struct work_struct reset_ws; }; MEMBERS
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. intf_assoc interface association descriptor 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) sysfs_files_created sysfs attributes exist ep_devs_created endpoint child pseudo-devices exist unregistering flag set when the interface is being unregistered needs_remote_wakeup flag set when the driver requires remote-wakeup capability during autosuspend. needs_altsetting0 flag set when a set-interface request for altsetting 0 has been deferred. needs_binding flag set when the driver should be re-probed or unbound following a reset or suspend operation it doesn't support. reset_running set to 1 if the interface is currently running a queued reset so that usb_cancel_queued_reset doesn't try to remove from the workqueue when running inside the worker thread. See __usb_queue_reset_device. dev driver model's view of this device usb_dev if an interface is bound to the USB major, this will point to the sysfs representation for that device. pm_usage_cnt PM usage counter for this interface reset_ws Used for scheduling resets from atomic context. DESCRIPTION
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 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. COPYRIGHT
Kernel Hackers Manual 2.6. July 2010 STRUCT USB_INTERFACE(9)