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USBNET(9) NetBSD Kernel Developer's Manual USBNET(9)
Powered by man-cgi (2021-06-01).
Maintained for NetBSD
by Kimmo Suominen.
Based on man-cgi by Panagiotis Christias.
usbnet -- common USB Ethernet driver framework
Functions offered by usbnet.h
usbnet_set_link(struct usbnet *un, bool link);
struct ifnet *
usbnet_ifp(struct usbnet *un);
struct ethercom *
usbnet_ec(struct usbnet *un);
struct mii_data *
usbnet_mii(struct usbnet *un);
usbnet_rndsrc(struct usbnet *un);
usbnet_softc(struct usbnet *un);
usbnet_havelink(struct usbnet *un);
usbnet_ispromisc(struct usbnet *un);
usbnet_isdying(struct usbnet *un);
usbnet_enqueue(struct usbnet *un, uint8_t *buf, size_t buflen,
int csum_flags, uint32_t csum_data, int mbuf_flags);
usbnet_input(struct usbnet *un, uint8_t *buf, size_t buflen);
usbnet_attach(struct usbnet *un);
usbnet_attach_ifp(struct usbnet *un, unsigned if_flags,
unsigned if_extflags, const struct usbnet_mii *unm);
usbnet_detach(device_t dev, int flags);
usbnet_activate(device_t dev, devact_t act);
The usbnet framework provides methods usable for USB Ethernet drivers.
The framework has support for these features:
· Partial autoconf handling
· USB endpoint pipe handling
· Rx and Tx chain handling
· Generic handlers or support for several struct ifnet call-
· Network stack locking protocol
· Interrupt handling
usbnet provides many or all of the traditional ``softc'' members inside
struct usbnet, which can be used directly as the device softc structure
if no additional storage is required. A structure exists for receive and
transmit chain management, struct usbnet_chain, that tracks the metadata
for each transfer descriptor available, minimum of one each for Rx and Tx
slot, and will be passed to the Rx and Tx callbacks.
There is a struct usbnet_ops structure that provides a number of optional
and required callbacks that will be described below.
For autoconfiguration the device attach routine is expected to ensure
that this device's struct usbnet is the first member of the device softc,
if it can not be used directly as the device softc, as well as set up the
necessary structure members, find end-points, find the Ethernet address
if relevant, call usbnet_attach(), set up interface, Ethernet, and MII
capabilities, and finally call usbnet_attach_ifp(). The device detach
routine should free any resources allocated by attach and then call
usbnet_detach(), possibly directly using usbnet_detach() as most con-
sumers have no additional resources not owned and released by the usbnet
framework itself. The device activate function should be set to
When bringing an interface up from if_init(9), which happens under
IFNET_LOCK(9), usbnet will:
1. call ``uno_init'' to initialize the hardware for sending and receiv-
2. open the USB pipes,
3. allocate Rx and Tx buffers for transfers,
4. call ``uno_mcast'' to initially program the hardware multicast fil-
ter, and finally
5. start the Rx transfers so packets can be received.
See the RECEIVE AND SEND section for details on using the chains.
When bringing an interface down from if_stop(9), which happens under
IFNET_LOCK(9), usbnet will:
1. abort the USB pipes,
2. call ``uno_stop'' to stop the hardware from receiving packets
(unless the device is detaching),
3. free Rx and Tx buffers for transfers, and
4. close the USB pipes.
For interface ioctl, most of the handling is in the framework. While the
interface is running, the optional ``uno_mcast'' callback is invoked
after handling the SIOCADDMULTI and SIOCDELMULTI ioctl commands to update
the hardware's multicast filter from the ethersubr(9) lists. The
optional ``uno_ioctl'' callback, which is invoked under IFNET_LOCK(9),
can be used to program special settings like offload handling.
If ioctl handling requires capturing device-specific ioctls then the
``uno_override_ioctl'' callback may be used instead to replace the frame-
work's ioctl handler completely (i.e., the replacement should call any
generic ioctl handlers such as ether_ioctl() as required.) For sending
packets, the ``uno_tx_prepare'' callback must be used to convert an mbuf
into a chain buffer ready for transmission.
For devices requiring MII handling there are callbacks for reading and
writing registers, and for status change events. Access to all the MII
functions is serialized by usbnet.
As receive must handle the case of multiple packets in one buffer, the
support is split between the driver and the framework. A ``uno_rx_loop''
callback must be provided that loops over the incoming packet data found
in a chain, performs necessary checking and passes the network frame up
the stack via either usbnet_enqueue() or usbnet_input(). Typically Eth-
ernet devices prefer usbnet_enqueue().
General accessor functions for struct usbnet:
Set the link status for this un to link.
Returns pointer to this un's struct ifnet.
Returns pointer to this un's struct ethercom.
Returns pointer to this un's struct mii_data.
Returns pointer to this un's krndsource_t.
Returns pointer to this un's device softc.
Returns true if link is active.
True if IFF_PROMISC is enabled, false if not.
May be used only in ``uno_init'' and ``uno_mcast''.
Drivers must use this in ``uno_mcast'' instead of reading
Returns true if device is dying (has been pulled or deactivated,
pending detach). This should be used only to abort timeout loops
Buffer enqueue handling for struct usbnet:
usbnet_enqueue(un, buf, buflen, csum_flags, csum_data, mbuf_flags)
Enqueue buffer buf for length buflen with higher layers, using the
provided csum_flags, and csum_data, which are written directly to
the mbuf packet header, and mbuf_flags, which is or-ed into the
mbuf flags for the created mbuf.
usbnet_input(un, buf, buflen)
Enqueue buffer buf for length buflen with higher layers.
Autoconfiguration handling for struct usbnet. See the AUTOCONFIGURATION
section for more details about these functions.
Initial stage attach of a usb network device. Performs internal
initialization and memory allocation only -- nothing is published
usbnet_attach_ifp(un, if_flags, if_extflags, unm)
Final stage attach of usb network device. Publishes the network
interface to the rest of the system.
If the passed in unm is non-NULL then an MII interface will be cre-
ated using the values provided in the struct usbnet_mii structure,
which has these members passed to mii_attach():
un_mii_capmask Capability mask.
un_mii_phyloc PHY location.
un_mii_offset PHY offset.
A default unm can be set using the USBNET_MII_DECL_DEFAULT() macro.
The if_flags and if_extflags will be or-ed into the interface flags
Device detach. Stops all activity and frees memory. Usable as
driver(9) detach method.
Device activate (deactivate) method. Usable as driver(9) activate
The framework expects the usbnet structure to have these members filled
in with valid values or functions:
un_sc Real softc allocated by autoconf and provided to attach, should
be set to the usbnet structure if no device-specific softc is
un_dev device_t saved in attach, used for messages mostly.
The USB iface handle for data interactions, see
usbd_device2interface_handle() for more details.
The struct usbd_device for this device, provided as the
usb_attach_arg's uaa_device member.
un_ops Points to a struct usbnet_ops structure which contains these mem-
void (*uno_stop)(struct ifnet *ifp, int disable)
Stop hardware activity (optional). Called under
IFNET_LOCK(9) when bringing the interface down, but skipped
when the device is detaching.
int (*uno_ioctl)(struct ifnet *ifp, u_long cmd, void *data)
Handle driver-specific ioctls (optional). Called under
void (*uno_mcast)(struct ifnet *)
Program hardware multicast filters from ethersubr(9) lists
(optional). Called between, and not during, ``uno_init''
int (*uno_override_ioctl)(struct ifnet *ifp, u_long cmd, void
Handle all ioctls, including standard ethernet ioctls nor-
mally handled internally by usbnet (optional). May or may
not be called under IFNET_LOCK(9).
int (*uno_init)(struct ifnet *ifp)
Initialize hardware activity (optional). Called under
IFNET_LOCK(9) when bringing the interface up.
int (*uno_read_reg)(struct usbnet *un, int phy, int reg, uint16_t
Read MII register. Required with MII. Serialized with
other MII functions, and only called after ``uno_init'' and
int (*uno_write_reg)(struct usbnet *un, int phy, int reg,
Write MII register. Required with MII. Serialized with
other MII functions, and only called after ``uno_init'' and
usbd_status (*uno_statchg)(struct ifnet *ifp)
Handle MII status change. Required with MII. Serialized
with other MII functions, and only called after
``uno_init'' and before ``uno_stop''.
unsigned (*uno_tx_prepare)(struct usbnet *un, struct mbuf *m,
struct usbnet_chain *c)
Prepare an mbuf for transmit. Required. Called sequen-
tially between, and not during, ``uno_init'' and
void (*uno_rx_loop)(struct usbnet *un, struct usbnet_chain *c,
Prepare one or more chain for enqueue. Required. Called
sequentially between, and not during, ``uno_init'' and
void (*uno_intr)(struct usbnet *un, usbd_status status)
Process periodic interrupt (optional). Called sequentially
between, and not during, ``uno_init'' and ``uno_stop''.
void (*uno_tick)(struct usbnet *un)
Called every second with USB task thread context
(optional). Called sequentially between, and not during,
``uno_init'' and ``uno_stop''.
Points to a struct usbnet_intr structure which should have these
If non-NULL, points to a buffer passed to
usbd_open_pipe_intr() in the device init callback, along
with the size and interval.
Size of interrupt pipe buffer.
Frequency of the interrupt in milliseconds.
un_ed Array of endpoint descriptors. There indexes are provided:
USBNET_ENDPT_RX, USBNET_ENDPT_TX, and USBNET_ENDPT_INTR. The Rx
and Tx endpoints are required.
MII phy number. Not used by usbnet.
6 bytes of Ethernet address that must be provided before calling
usbnet_attach_ifp() if the device has Ethernet.
Device owned flags word. The usbnet framework will not touch
Passed to usbd_setup_xfer() for receiving packets.
Passed to usbd_setup_xfer() for sending packets.
Number of chain elements to allocate for Rx.
Number of chain elements to allocate for Tx.
Rx buffer size.
Tx buffer size.
The device detach and activate callbacks can typically be set to
usbnet_detach() and usbnet_activate() unless device-specific handling is
required, in which case, they can be called before or after such han-
The capabilities described in both struct ifp and struct ethercom must be
set before calling usbnet_attach_ifp().
RECEIVE AND SEND
Receive and send routines are structured around the usbnet_cdata and
usbnet_chain structures, the un_ed, un_rx_xfer_flags, and
un_tx_xfer_flags members, and the uno_init(), uno_tx_prepare(),
uno_rx_loop(), and uno_stop() callbacks of usbnet_ops.
Typically, the device attach routine will fill in members of the usbnet
structure, as listed in AUTOCONFIGURATION. The un_ed array should have
the USBNET_ENDPT_RX and USBNET_ENDPT_TX array entries filled in, and
optionally the USBNET_ENDPT_INTR entry filled in if applicable.
The uno_init() callback enables the hardware, and if necessary reprograms
the hardware multicast filter, before the framework initiates USB Tx/Rx
transfers. All USB transfer setup is handled by the framework. The
driver callbacks merely copy data in or out of a chain entry using what
is typically a device-specific method.
The uno_rx_loop() callback, called sequentially, converts the provided
usbnet_chain data and length into a series (one or more) of packets that
are enqueued with the higher layers using either usbnet_enqueue() (for
most devices) or usbnet_input() for devices that use if_input(). (This
currently relies upon the struct ifnet having the ``_if_input'' member
set as well, which is true for current consumers.)
The uno_tx_prepare() callback must convert the provided struct mbuf into
the provided struct usbnet_chain performing any device-specific padding,
checksum, header or other. Note that this callback must check that it is
not attempting to copy more than the chain buffer size, as set in the
usbnet ``un_tx_bufsz'' member. This callback is only called once per
The struct usbnet_chain structure which contains a ``unc_buf'' member
which has the chain buffer allocated where data should be copied to or
from for receive or transmit operations. It also contains pointers back
to the owning struct usbnet, and the struct usbd_xfer associated with
After aborting all USB Tx/Rx transfers when bringing an interface down,
the framework calls the optional uno_stop() callback to disable the hard-
For devices that have MII support these callbacks in struct usbnet_ops
must be provided:
Read an MII register for a particular PHY. Returns standard
errno(2). Must initialize the result even on failure.
Write an MII register for a particular PHY. Returns standard
Handle a status change event for this interface.
The interrupt specific callback, ``uno_intr'', is an optional callback
that can be called periodically, registered by usbnet using the
usbd_open_pipe_intr() function (instead of the usbd_open_pipe() func-
tion.) The usbnet framework provides most of the interrupt handling and
the callback simply inspects the returned buffer as necessary. To enable
the this callback point the struct usbnet member ``un_intr'' to a struct
usbnet_intr structure with these members set:
Data buffer for interrupt status relies.
Size of the above buffer.
Interval in millieconds.
These values will be passed to usbd_open_pipe_intr().
CONVERTING OLD-STYLE DRIVERS
The porting of an older driver to the usbnet framework is largely an
effort in deleting code. The process involves making these changes:
Many headers are included in usbnet.h and can be removed from the
driver, as well as headers no longer used, such as callout.h and
The majority of the driver's existing ``softc'' structure can
likely be replaced with usage of struct usbnet and its related
functionality. This includes at least the device_t pointer, Ether-
net address, the ethercom and mii_data structures, end point
descriptors, usbd device, interface, and task and callout struc-
tures (both these probably go away entirely) and all the associated
watchdog handling, timevals, list size, buffer size and xfer flags
for both Rx, and Tx, and interrupt notices, interface flags, device
link, PHY number, chain data, locks including Rx, Tx, and MII.
There is a driver-only ``un_flags'' in the usbnet structure avail-
able for drivers to use.
Many drivers can use the usbnet structure as the device private
storage passed to CFATTACH_DECL_NEW. Many internal functions to
the driver may look better if switched to operate on the device's
usbnet as, for example, the usbd_device value is now available (and
must be set by the driver) in the usbnet, which may be needed for
any call to usbd_do_request(). The standard endpoint values must
be stored in the usbnet ``un_ed'' array.
As usbnet manages xfer chains all code related to the opening,
closing, aborting and transferring of data on pipes is performed by
the framework based upon the buffer size and more provided in
subnet, so all code related to them should be deleted.
The vast majority of interface specific code should be deleted.
For device-specific interface values, the ifnet flags and exflags
can be set, as well as the ethercom ``ec_capabilities'' member,
before calling usbnet_attach_ifp(). All calls to ifmedia_init(),
mii_attach(), ifmedia_add(), ifmedia_set(), if_attach(),
ether_ifattach(), rnd_attach_source(), and usbd_add_drv_event()
should be eliminated. The device ``ioctl'' routine can use the
default handling with a callback for additional device specific
programming (multicast filters, etc.), which can be empty, or, the
override ioctl can be used for heavier requirements. The device
``stop'' routine is replaced with a simple call that turns off the
device-specific transmitter and receiver if necessary, as the
framework handles pipes and transfers and buffers.
For devices with MII support the three normal callbacks (read,
write, and status change) must be converted to usbnet. Local
``link'' variables need to be replaced with accesses to
usbnet_set_link() and usbnet_havelink(). Other ifmedia callbacks
that were passed to ifmedia_init() should be deleted and any work
moved into ``uno_statchg''.
Receive and Transmit
The usbnet framework handles the majority of handling of both net-
work directions. The interface init routine should keep all of the
device specific setup but replace all pipe management with a call
to usbnet_init_rx_tx(). The typical receive handling will normally
be replaced with a receive loop functions that can accept one or
more packets, ``uno_rx_loop'', which can use either
usbnet_enqueue() or usbnet_input() to pass the packets up to higher
layers. The typical interface ``if_start'' function and any addi-
tional functions used will normal be replaced with a relatively
simple ``uno_tx_prepare'' function that simply converts an mbuf
into a usbnet_chain useful for this device that will be passed onto
usbd_transfer(). The framework's handling of the Tx interrupt is
Interrupt pipe handling
For devices requiring special handling of the interrupt pipe (i.e.,
they use the usbd_open_pipe_intr() method), most of the interrupt
handler should be deleted, leaving only code that inspects the
result of the interrupt transfer.
It's common to forget to set link active on devices with MII. Be
sure to call usbnet_set_link() during any status change event.
Many locking issues are hidden without LOCKDEBUG, including hard-
hangs. It's highly recommended to develop with LOCKDEBUG.
The usbnet ``un_ed'' array is unsigned and should use ``0'' as the
usb(4), driver(9), usbd_status(9), usbdi(9)
This usbnet interface first appeared in NetBSD 9.0. Portions of the
original design are based upon ideas from Nick Hudson <skrll@NetBSD.org>.
Matthew R. Green <firstname.lastname@example.org>
NetBSD 10.99 March 15, 2020 NetBSD 10.99