usb_ifnum_to_if(9) [centos man page]

USB_IFNUM_TO_IF(9)						   USB Core APIs						USB_IFNUM_TO_IF(9)

NAME

       usb_ifnum_to_if - get the interface object with a given interface number

SYNOPSIS

       struct usb_interface * usb_ifnum_to_if(const struct usb_device * dev, unsigned ifnum);

ARGUMENTS

       dev
	   the device whose current configuration is considered

       ifnum
	   the desired interface

DESCRIPTION

       This walks the device descriptor for the currently active configuration to find the interface object with the particular interface number.

       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!

RETURN

       A pointer to the interface that has ifnum as interface number, if found.  NULL otherwise.

COPYRIGHT

Kernel Hackers Manual 3.10					     June 2014							USB_IFNUM_TO_IF(9)

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).

RETURN

       Zero on success, or else the status code returned by the underlying usb_control_msg call.

COPYRIGHT

Kernel Hackers Manual 3.10					     June 2014						      USB_SET_INTERFACE(9)