UM0851 datasheet(74/245 Pages) STMICROELECTRONICS

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Communication device drivers

UM0851

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Doc ID 16604 Rev 2

ss->function.disable = sourcesink_disable;

ss->function.suspend = sourcesink_suspend;

ss->function.resume = sourcesink_resume;

status = usb_add_function(c, &ss->function);

if (status)

kfree(ss);

return status;

}

Initializing USB descriptors

There are some fields in standard USB descriptors that require inputs from the composite

layer for initialization. In almost all descriptors some of these fields are indexed to string

tables and to an interface number for the interface descriptors. For this there are some

helper routines which are described below.

static int zero_bind(struct usb_composite_dev *cdev)

{

/* get next available string index */

id = usb_string_id(cdev);

if (id < 0)

return id;

strings_dev[STRING_MANUFACTURER_IDX].id = id;

device_desc.iManufacturer = id;

...

}

static int sourcesink_bind(struct usb_configuration *c, struct usb_function *f)

{

...

/* allocate interface ID(s) */

id = usb_interface_id(c, f);

if (id < 0)

return id;

source_sink_intf.bInterfaceNumber = id;

...

}

Data and control transfer

After completing the registering process, the gadget driver can handle setup requests

through setup callbacks. In this way, you can configure other required endpoints and initiate

a transfer (of control or data) through Linux gadget framework APIs. You can obtain more

details on these APIs through references.The following table summarizes these APIs and

their purpose.

Table 22.

Linux gadget endpoint APIs

API

Description

struct usb_ep *usb_ep_autoconfig(struct

usb_gadget *, struct usb_endpoint descriptor *)

Allocates a suitable free endpoint described by

struct usb_endpoint_descriptor

int usb_ep_enable(struct usb_ep *ep, const struct

usb_endpoint_descriptor *desc)

Enables the endpoint ep, in order to be used for

data transfer. The endpoint ep is described in

struct usb_endpoint_descriptor

struct usb_request *usb_ep_alloc_request(struct

usb_ep *ep, gfp_t gfp_flags)

Allocates a request for USB transfer

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