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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_CONFIGURA(9) Kernel Mode Gadget API STRUCT USB_CONFIGURA(9) NAME
struct_usb_configuration - represents one gadget configuration SYNOPSIS
struct usb_configuration { const char * label; struct usb_gadget_strings ** strings; const struct usb_descriptor_header ** descriptors; int (* bind) (struct usb_configuration *); void (* unbind) (struct usb_configuration *); int (* setup) (struct usb_configuration *,const struct usb_ctrlrequest *); u8 bConfigurationValue; u8 iConfiguration; u8 bmAttributes; u8 bMaxPower; struct usb_composite_dev * cdev; }; MEMBERS
label For diagnostics, describes the configuration. strings Tables of strings, keyed by identifiers assigned during bind() and by language IDs provided in control requests. descriptors Table of descriptors preceding all function descriptors. Examples include OTG and vendor-specific descriptors. bind Called from usb_add_config() to allocate resources unique to this configuration and to call usb_add_function() for each function used. unbind Reverses bind; called as a side effect of unregistering the driver which added this configuration. setup Used to delegate control requests that aren't handled by standard device infrastructure or directed at a specific interface. bConfigurationValue Copied into configuration descriptor. iConfiguration Copied into configuration descriptor. bmAttributes Copied into configuration descriptor. bMaxPower Copied into configuration descriptor. cdev assigned by usb_add_config() before calling bind(); this is the device associated with this configuration. DESCRIPTION
Configurations are building blocks for gadget drivers structured around function drivers. Simple USB gadgets require only one function and one configuration, and handle dual-speed hardware by always providing the same functionality. Slightly more complex gadgets may have more than one single-function configuration at a given speed; or have configurations that only work at one speed. Composite devices are, by definition, ones with configurations which include more than one function. The lifecycle of a usb_configuration includes allocation, initialization of the fields described above, and calling usb_add_config() to set up internal data and bind it to a specific device. The configuration's bind() method is then used to initialize all the functions and then call usb_add_function() for them. Those functions would normally be independant of each other, but that's not mandatory. CDC WMC devices are an example where functions often depend on other functions, with some functions subsidiary to others. Such interdependency may be managed in any way, so long as all of the descriptors complete by the time the composite driver returns from its bind routine. AUTHOR
David Brownell <dbrownell@users.sourceforge.net> Author. COPYRIGHT
Kernel Hackers Manual 2.6. July 2010 STRUCT USB_CONFIGURA(9)

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