centos man page for usb_control_msg

USB_CONTROL_MSG(9)						   USB Core APIs						USB_CONTROL_MSG(9)

NAME
       usb_control_msg - Builds a control urb, sends it off and waits for completion

SYNOPSIS
       int usb_control_msg(struct usb_device * dev, unsigned int pipe, __u8 request, __u8 requesttype, __u16 value, __u16 index, void * data,
			   __u16 size, int timeout);

ARGUMENTS
       dev
	   pointer to the usb device to send the message to

       pipe
	   endpoint "pipe" to send the message to

       request
	   USB message request value

       requesttype
	   USB message request type value

       value
	   USB message value

       index
	   USB message index value

       data
	   pointer to the data to send

       size
	   length in bytes of the data to send

       timeout
	   time in msecs to wait for the message to complete before timing out (if 0 the wait is forever)

CONTEXT
       !in_interrupt ()

DESCRIPTION
       This function sends a simple control message to a specified endpoint and waits for the message to complete, or timeout.

       Don't use this function from within an interrupt context, like a bottom half handler. If you need an asynchronous message, or need to send
       a message from within interrupt context, use usb_submit_urb. If a thread in your driver uses this call, make sure your disconnect method
       can wait for it to complete. Since you don't have a handle on the URB used, you can't cancel the request.

RETURN
       If successful, the number of bytes transferred. Otherwise, a negative error number.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014							USB_CONTROL_MSG(9)