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
struct usb_interface * usb_ifnum_to_if(const struct usb_device * dev, unsigned ifnum);
the device whose current configuration is considered
the desired interface
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!
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)
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USB_SET_INTERFACE(9) USB Core APIs USB_SET_INTERFACE(9)NAME
usb_set_interface - Makes a particular alternate setting be current
int usb_set_interface(struct usb_device * dev, int interface, int alternate);
the device whose interface is being updated
the interface being updated
the setting being chosen.
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).
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)
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