other versions
STRUCT USB_FUNCTION(9) | Kernel Mode Gadget API | STRUCT USB_FUNCTION(9) |
NAME¶
struct_usb_function - describes one function of a configurationSYNOPSIS¶
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_descriptor_header ** ssp_descriptors; struct usb_configuration * config; struct usb_os_desc_table * os_desc_table; unsigned os_desc_n; 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 *); bool (* req_match) (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¶
nameFor 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.
ssp_descriptors
Table of super speed plus 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
plus.
config
assigned when usb_add_function() is called; this
is the configuration with which this function is associated.
os_desc_table
Table of (interface id, os descriptors) pairs. The
function can expose more than one interface. If an interface is a member of an
IAD, only the first interface of IAD has its entry in the table.
os_desc_n
Number of entries in os_desc_table
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.
req_match
Tests if a given class request can be handled by this
function.
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 recipient 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¶
January 2017 | Kernel Hackers Manual 4.8. |