struct usb_function — describes one function of a configuration
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 *,bool config0); 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); };
const char * name
For diagnostics, identifies the function.
struct usb_gadget_strings ** strings
tables of strings, keyed by identifiers assigned during bind
and by language IDs provided in control requests
struct usb_descriptor_header ** 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).
struct usb_descriptor_header ** 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.
struct usb_descriptor_header ** 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.
struct usb_descriptor_header ** 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.
struct usb_configuration * config
assigned when usb_add_function
() is called; this is the
configuration with which this function is associated.
struct usb_os_desc_table * 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.
unsigned os_desc_n
Number of entries in os_desc_table
int (*)(struct usb_configuration *,struct usb_function *) 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.
void (*)(struct usb_configuration *,struct usb_function *) unbind
Reverses bind
; called as a side effect of unregistering the
driver which added this function.
void (*)(struct usb_function *f) free_func
free the struct usb_function.
struct module * mod
(internal) points to the module that created this structure.
int (*)(struct usb_function *,unsigned interface, unsigned alt) 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.
int (*)(struct usb_function *,unsigned interface) get_alt
Returns the active altsetting. If this is not provided, then only altsetting zero is supported.
void (*)(struct usb_function *) disable
(REQUIRED) Indicates the function should be disabled. Reasons include host resetting or reconfiguring the gadget, and disconnection.
int (*)(struct usb_function *,const struct usb_ctrlrequest *) setup
Used for interface-specific control requests.
bool (*)(struct usb_function *,const struct usb_ctrlrequest *,bool config0) req_match
Tests if a given class request can be handled by this function.
void (*)(struct usb_function *) suspend
Notifies functions when the host stops sending USB traffic.
void (*)(struct usb_function *) resume
Notifies functions when the host restarts USB traffic.
int (*)(struct usb_function *) get_status
Returns function status as a reply to
GetStatus
request when the recipient is Interface.
int (*)(struct usb_function *,u8 suspend_opt) func_suspend
callback to be called when SetFeature(FUNCTION_SUSPEND) is reseived
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.