Revised: 2002-Feb-09.

This is the documentation of (hopefully) all possible error codes (and
their interpretation) that can be returned from usbcore.

Some of them are returned by the Host Controller Drivers (HCDs), which
device drivers only see through usbcore.  As a rule, all the HCDs should
behave the same except for transfer speed dependent behaviors.


**************************************************************************
*                   Error codes returned by usb_submit_urb               *
**************************************************************************

Non-USB-specific:

0		URB submission went fine

-ENOMEM		no memory for allocation of internal structures	

USB-specific:

-ENODEV		specified USB-device or bus doesn't exist

-ENXIO		a control or interrupt URB is already queued to this endpoint;
		or (UHCI only) a bulk URB is already queued to this endpoint
		and USB_QUEUE_BULK wasn't used

-EINVAL		a) Invalid transfer type specified (or not supported)
		b) Invalid interrupt interval (0<=n<256)
		c) more than one interrupt packet requested
		d) ISO: number_of_packets is < 0

-EAGAIN		a) specified ISO start frame too early
		b) (using ISO-ASAP) too much scheduled for the future
		   wait some time and try again.

-EFBIG		too much ISO frames requested (currently uhci>900)

-EPIPE		Specified endpoint is stalled.  For non-control endpoints,
		reset this status with usb_clear_halt().

-EMSGSIZE	endpoint message size is zero, do interface/alternate setting

-ENOSPC		The host controller's bandwidth is already consumed and
		this request would push it past its allowed limit.

-ESHUTDOWN	The host controller has been disabled due to some
		problem that could not be worked around.


**************************************************************************
*                   Error codes returned by in urb->status               *
*                   or in iso_frame_desc[n].status (for ISO)             *
**************************************************************************

USB device drivers may only test urb status values in completion handlers.
This is because otherwise there would be a race between HCDs updating
these values on one CPU, and device drivers testing them on another CPU.

A transfer's actual_length may be positive even when an error has been
reported.  That's because transfers often involve several packets, so that
one or more packets could finish before an error stops further endpoint I/O.


0			Transfer completed successfully

-ENOENT			URB was synchronously unlinked by usb_unlink_urb

-EINPROGRESS		URB still pending, no results yet
			(That is, if drivers see this it's a bug.)

-EPROTO (*)		a) bitstuff error
			b) unknown USB error 

-EILSEQ (*)		CRC mismatch

-EPIPE			Endpoint stalled.  For non-control endpoints,
			reset this status with usb_clear_halt().

-ECOMM			During an IN transfer, the host controller
			received data from an endpoint faster than it
			could be written to system memory

-ENOSR			During an OUT transfer, the host controller
			could not retrieve data from system memory fast
			enough to keep up with the USB data rate

-EOVERFLOW (*)		The amount of data returned by the endpoint was
			greater than either the max packet size of the
			endpoint or the remaining buffer size.  "Babble".

-EREMOTEIO		The endpoint returned less than max packet size
			and that amount did not fill the specified buffer
			(and USB_DISBLE_SPD was not set in transfer_flags)

-ETIMEDOUT		transfer timed out, NAK

-ENODEV			Device was removed.  Often preceded by a burst of
			other errors, since the hub driver does't detect
			device removal events immediately.

-EXDEV			ISO transfer only partially completed
			look at individual frame status for details

-EINVAL			ISO madness, if this happens: Log off and go home

-ECONNRESET		URB was asynchronously unlinked by usb_unlink_urb

-ESHUTDOWN		The host controller has been disabled due to some
			problem that could not be worked around.


(*) Error codes like -EPROTO, -EILSEQ and -EOVERFLOW normally indicate
hardware problems such as bad devices (including firmware) or cables.



**************************************************************************
*              Error codes returned by usbcore-functions                 *
*           (expect also other submit and transfer status codes)         *
**************************************************************************

usb_register():
-EINVAL			error during registering new driver

usb_get_*/usb_set_*():
usb_control_msg():
usb_bulk_msg():
			All USB errors (submit/status) can occur
