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usb_add_function(9) [centos man page]

USB_ADD_FUNCTION(9)					      Kernel Mode Gadget API					       USB_ADD_FUNCTION(9)

NAME
usb_add_function - add a function to a configuration SYNOPSIS
int usb_add_function(struct usb_configuration * config, struct usb_function * function); ARGUMENTS
config the configuration function the function being added CONTEXT
single threaded during gadget setup DESCRIPTION
After initialization, each configuration must have one or more functions added to it. Adding a function involves calling its bind() method to allocate resources such as interface and string identifiers and endpoints. This function returns the value of the function's bind, which is zero for success else a negative errno value. AUTHOR
David Brownell <dbrownell@users.sourceforge.net> Author. COPYRIGHT
Kernel Hackers Manual 3.10 June 2014 USB_ADD_FUNCTION(9)

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STRUCT 
USB_FUNCTION(9) Kernel Mode Gadget API STRUCT USB_FUNCTION(9) NAME
struct_usb_function - describes one function of a configuration SYNOPSIS
struct usb_function { const char * name; struct usb_gadget_strings ** strings; struct usb_descriptor_header ** fs_descriptors; struct usb_descriptor_header ** hs_descriptors; struct usb_descriptor_header ** ss_descriptors; struct usb_configuration * config; int (* bind) (struct usb_configuration *,struct usb_function *); void (* unbind) (struct usb_configuration *,struct usb_function *); void (* free_func) (struct usb_function *f); struct module * mod; int (* set_alt) (struct usb_function *,unsigned interface, unsigned alt); int (* get_alt) (struct usb_function *,unsigned interface); void (* disable) (struct usb_function *); int (* setup) (struct usb_function *,const struct usb_ctrlrequest *); void (* suspend) (struct usb_function *); void (* resume) (struct usb_function *); int (* get_status) (struct usb_function *); int (* func_suspend) (struct usb_function *,u8 suspend_opt); }; MEMBERS
name For diagnostics, identifies the function. strings tables of strings, keyed by identifiers assigned during bind and by language IDs provided in control requests fs_descriptors Table of full (or low) speed descriptors, using interface and string identifiers assigned during bind(). If this pointer is null, the function will not be available at full speed (or at low speed). hs_descriptors Table of high speed descriptors, using interface and string identifiers assigned during bind(). If this pointer is null, the function will not be available at high speed. ss_descriptors Table of super speed descriptors, using interface and string identifiers assigned during bind(). If this pointer is null after initiation, the function will not be available at super speed. config assigned when usb_add_function() is called; this is the configuration with which this function is associated. bind Before the gadget can register, all of its functions bind to the available resources including string and interface identifiers used in interface or class descriptors; endpoints; I/O buffers; and so on. unbind Reverses bind; called as a side effect of unregistering the driver which added this function. free_func free the struct usb_function. mod (internal) points to the module that created this structure. set_alt (REQUIRED) Reconfigures altsettings; function drivers may initialize usb_ep.driver data at this time (when it is used). Note that setting an interface to its current altsetting resets interface state, and that all interfaces have a disabled state. get_alt Returns the active altsetting. If this is not provided, then only altsetting zero is supported. disable (REQUIRED) Indicates the function should be disabled. Reasons include host resetting or reconfiguring the gadget, and disconnection. setup Used for interface-specific control requests. suspend Notifies functions when the host stops sending USB traffic. resume Notifies functions when the host restarts USB traffic. get_status Returns function status as a reply to GetStatus request when the recepient is Interface. func_suspend callback to be called when SetFeature(FUNCTION_SUSPEND) is reseived DESCRIPTION
A single USB function uses one or more interfaces, and should in most cases support operation at both full and high speeds. Each function is associated by usb_add_function() with a one configuration; that function causes bind() to be called so resources can be allocated as part of setting up a gadget driver. Those resources include endpoints, which should be allocated using usb_ep_autoconfig(). To support dual speed operation, a function driver provides descriptors for both high and full speed operation. Except in rare cases that don't involve bulk endpoints, each speed needs different endpoint descriptors. Function drivers choose their own strategies for managing instance data. The simplest strategy just declares it "static', which means the function can only be activated once. If the function needs to be exposed in more than one configuration at a given speed, it needs to support multiple usb_function structures (one for each configuration). A more complex strategy might encapsulate a usb_function structure inside a driver-specific instance structure to allows multiple activations. An example of multiple activations might be a CDC ACM function that supports two or more distinct instances within the same configuration, providing several independent logical data links to a USB host. AUTHOR
David Brownell <dbrownell@users.sourceforge.net> Author. COPYRIGHT
Kernel Hackers Manual 3.10 June 2014 STRUCT USB_FUNCTION(9)

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