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+Revised: 2004-Oct-21
+
+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 and the
+way certain faults are reported.
+
+
+**************************************************************************
+* 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
+
+-ENOENT specified interface or endpoint does not exist or
+ is not enabled
+
+-ENXIO host controller driver does not support queuing of this type
+ of urb. (treat as a host controller bug.)
+
+-EINVAL a) Invalid transfer type specified (or not supported)
+ b) Invalid or unsupported periodic transfer interval
+ c) ISO: attempted to change transfer interval
+ d) ISO: number_of_packets is < 0
+ e) various other cases
+
+-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 Host controller driver can't schedule that many ISO frames.
+
+-EPIPE Specified endpoint is stalled. For non-control endpoints,
+ reset this status with usb_clear_halt().
+
+-EMSGSIZE (a) endpoint maxpacket size is zero; it is not usable
+ in the current interface altsetting.
+ (b) ISO packet is biger than endpoint maxpacket
+ (c) requested data transfer size is invalid (negative)
+
+-ENOSPC This request would overcommit the usb bandwidth reserved
+ for periodic transfers (interrupt, isochronous).
+
+-ESHUTDOWN The device or host controller has been disabled due to some
+ problem that could not be worked around.
+
+-EPERM Submission failed because urb->reject was set.
+
+-EHOSTUNREACH URB was rejected because the device is suspended.
+
+
+**************************************************************************
+* 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) no response packet received within the
+ prescribed bus turn-around time
+ c) unknown USB error
+
+-EILSEQ (*, **) a) CRC mismatch
+ b) no response packet received within the
+ prescribed bus turn-around time
+ c) unknown USB error
+
+ Note that often the controller hardware does not
+ distinguish among cases a), b), and c), so a
+ driver cannot tell whether there was a protocol
+ error, a failure to respond (often caused by
+ device disconnect), or some other fault.
+
+-ETIMEDOUT (**) No response packet received within the prescribed
+ bus turn-around time. This error may instead be
+ reported as -EPROTO or -EILSEQ.
+
+ Note that the synchronous USB message functions
+ also use this code to indicate timeout expired
+ before the transfer completed.
+
+-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 data read from the endpoint did not fill the
+ specified buffer, and URB_SHORT_NOT_OK was set in
+ urb->transfer_flags.
+
+-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 device or host controller has been disabled due
+ to some problem that could not be worked around,
+ such as a physical disconnect.
+
+
+(*) Error codes like -EPROTO, -EILSEQ and -EOVERFLOW normally indicate
+hardware problems such as bad devices (including firmware) or cables.
+
+(**) This is also one of several codes that different kinds of host
+controller use to to indicate a transfer has failed because of device
+disconnect. In the interval before the hub driver starts disconnect
+processing, devices may receive such fault reports for every request.
+
+
+
+**************************************************************************
+* 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():
+-ETIMEDOUT Timeout expired before the transfer completed.
+ In the future this code may change to -ETIME,
+ whose definition is a closer match to this sort
+ of error.
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