'\" t
.\"     Title: struct usb_host_config
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: January 2017
.\"    Manual: Host-Side Data Types and Macros
.\"    Source: Kernel Hackers Manual 4.8.15
.\"  Language: English
.\"
.TH "STRUCT USB_HOST_CONF" "9" "January 2017" "Kernel Hackers Manual 4\&.8\&." "Host-Side Data Types and Macro"
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.SH "NAME"
struct_usb_host_config \- representation of a device\*(Aqs configuration
.SH "SYNOPSIS"
.sp
.nf
struct usb_host_config {
  struct usb_config_descriptor desc;
  char * string;
  struct usb_interface_assoc_descriptor * intf_assoc[USB_MAXIADS];
  struct usb_interface * interface[USB_MAXINTERFACES];
  struct usb_interface_cache * intf_cache[USB_MAXINTERFACES];
  unsigned char * extra;
  int extralen;
};  
.fi
.SH "MEMBERS"
.PP
desc
.RS 4
the device\*(Aqs configuration descriptor\&.
.RE
.PP
string
.RS 4
pointer to the cached version of the iConfiguration string, if present for this configuration\&.
.RE
.PP
intf_assoc[USB_MAXIADS]
.RS 4
list of any interface association descriptors in this config
.RE
.PP
interface[USB_MAXINTERFACES]
.RS 4
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\&.
.RE
.PP
intf_cache[USB_MAXINTERFACES]
.RS 4
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\&.
.RE
.PP
extra
.RS 4
pointer to buffer containing all extra descriptors associated with this configuration (those preceding the first interface descriptor)\&.
.RE
.PP
extralen
.RS 4
length of the extra descriptors buffer\&.
.RE
.SH "DESCRIPTION"
.PP
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\&.
.PP
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
\fBusb_ifnum_to_if\fR
to look up an interface entry based on its number\&.
.PP
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\*(Aqs desires (expressed through userspace tools)\&. However, drivers can call
\fBusb_reset_configuration\fR
to reinitialize the current configuration and all its interfaces\&.
.SH "COPYRIGHT"
.br