USBNET(9) | Kernel Developer's Manual | USBNET(9)

# NAME

`usbnet` —
common USB Ethernet driver framework

# SYNOPSIS

`#include <dev/usb/usbnet.h>`

## Functions offered by usbnet.h

void
`usbnet_set_link`(struct usbnet *un, bool link);

void
`usbnet_set_dying`(struct usbnet *un, bool dying);

struct ifnet *
`usbnet_ifp`(struct usbnet *un);

struct ethercom *
`usbnet_ec`(struct usbnet *un);

struct mii_data *
`usbnet_mii`(struct usbnet *un);

krndsource_t *
`usbnet_rndsrc`(struct usbnet *un);

void *
`usbnet_softc`(struct usbnet *un);

bool
`usbnet_havelink`(struct usbnet *un);

bool
`usbnet_isdying`(struct usbnet *un);

void
`usbnet_lock`(struct usbnet *un);

void
`usbnet_unlock`(struct usbnet *un);

kmutex_t *
`usbnet_mutex`(struct usbnet *un);

void
`usbnet_isowned`(struct usbnet *un);

void
`usbnet_lock_rx`(struct usbnet *un);

void
`usbnet_unlock_rx`(struct usbnet *un);

kmutex_t *
`usbnet_mutex_rx`(struct usbnet *un);

void
`usbnet_isowned_rx`(struct usbnet *un);

void
`usbnet_lock_tx`(struct usbnet *un);

void
`usbnet_unlock_tx`(struct usbnet *un);

kmutex_t *
`usbnet_mutex_tx`(struct usbnet *un);

void
`usbnet_isowned_tx`(struct usbnet *un);

int
`usbnet_init_rx_tx`(struct usbnet *un, unsigned rxflags, unsigned txflags);

void
`usbnet_lock_mii`(struct usbnet *un);

void
`usbnet_lock_mii_un_locked`(struct usbnet *un);

void
`usbnet_unlock_mii`(struct usbnet *un);

void
`usbnet_unlock_mii_un_locked`(struct usbnet *un);

kmutex_t *
`usbnet_mutex_mii`(struct usbnet *un);

void
`usbnet_isowned_mii`(struct usbnet *un);

int
`usbnet_miibus_readreg`(device_t dev, int phy, int reg, uint16_t *val);

int
`usbnet_miibus_writereg`(device_t dev, int phy, int reg, uint16_t val);

void
`usbnet_miibus_statchg`(struct ifnet *);

void
`usbnet_enqueue`(struct usbnet *un, uint8_t *buf, size_t buflen, int csum_flags, uint32_t csum_data, int mbuf_flags);

void
`usbnet_input`(struct usbnet *un, uint8_t *buf, size_t buflen);

void
`usbnet_attach`(struct usbnet *un, const char *detname);

void
`usbnet_attach_ifp`(struct usbnet *un, unsigned if_flags, unsigned if_extflags, const struct usbnet_mii *unm);

int
`usbnet_detach`(device_t dev, int flags);

int
`usbnet_activate`(device_t dev, devact_t act);

void
`usbnet_stop`(struct usbnet *un, struct ifnet *ifp, int disable);

# DESCRIPTION

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 callbacks
- MII bus locking
- 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 consumers have no additional resources not owned and released by the `usbnet` framework itself. The device activate function should be set to `usbnet_activate`().

To manage all Rx and Tx chains the “uno_init” callback of struct usbnet_ops should perform any device specific initialization and then call `usbnet_init_rx_tx`() which will allocate chains, set up and open pipes, and start the Rx transfers so that packets can arrived. These allocations and pipes can be closed and destroyed by calling `usbnet_stop`(). Both of `usbnet_init_rx_tx`() and `usbnet_stop`() must be called with the `usbnet` lock held, see `usbnet_lock`() and `usbnet_unlock`(). See the RECEIVE AND SEND section for details on using the chains.

The interface init, ioctl, start, and stop, routines are handled by the framework with callbacks for device-specific handling. For interface init (i.e., when bringing the interface up), the “uno_init” callback should perform any device specific initialization and then call `usbnet_init_rx_tx`() to finalize Rx and Tx queue initialization. For interface ioctl, most of the handling is in the framework and the optional “uno_ioctl” callback should be used to program special settings like multicast filters or offload handling. If ioctl handling requires capturing device-specific ioctls then the “uno_override_ioctl” callback may be used instead to replace the framework's ioctl handler completely (i.e., the replacement should call any generic ioctl handlers such as `ether_ioctl`() as required.) For interface start, the “uno_tx_prepare” callback must be used to convert an mbuf into a chain buffer ready for transmission. For interface stop, there is an optional “uno_stop” callback to turn off any chipset specific values if required.

For devices requiring MII handling there are callbacks for reading and writing registers, and for status change events. The framework provides an MII-specific lock per interface which will be held when calling these functions, and these locks should be used by internal code that also requires serialized access to registers with the `usbnet_lock_mii`(), `usbnet_unlock_mii`(), `usbnet_lock_mii_un_locked`(), and `usbnet_unlock_mii_un_locked`() functions. These functions handle device detach events safely, and as such take and release a reference on this device and use the usbnet lock for this. Sometimes the usbnet lock is already held and instead the “un_locked” versions should be used.

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 Ethernet devices prefer `usbnet_enqueue`().

General accessor functions for struct usbnet:

`usbnet_set_link`(un, link)
  Set the link status for this un to link.
`usbnet_set_dying`(un, dying)
  Set the dying status for this un to dying.
`usbnet_ifp`(un)
  Returns pointer to this un's struct ifnet.
`usbnet_ec`(un)
  Returns pointer to this un's struct ethercom.
`usbnet_mii`(un)
  Returns pointer to this un's struct mii_data.
`usbnet_rndsrc`(un)
  Returns pointer to this un's krndsource_t.
`usbnet_softc`(un)
  Returns pointer to this un's device softc.
`bool`(usbnet_havelink, un)
  Returns true if link is active.
`bool`(usbnet_isdying, un)
  Returns true if device is dying (has been pulled or deactivated, pending detach.)

Lock handling functions for struct usbnet:

`usbnet_lock`(un)
`usbnet_unlock`(un)
`usbnet_isowned`(un)
`usbnet_lock_rx`(un)
`usbnet_unlock_rx`(un)
`usbnet_isowned_rx`(un)
`usbnet_lock_tx`(un)
`usbnet_unlock_tx`(un)
`usbnet_isowned_tx`(un)
`usbnet_lock_mii`(un)
`usbnet_lock_mii_un_locked`(un)
`usbnet_unlock_mii`(un)
`usbnet_unlock_mii_un_locked`(un)
`usbnet_isowned_mii`(un)
  These groups of three or five functions provide methods to lock, unlock, and assert ownership of one of the four locks provided by `usbnet`. The four locks are the “softc” lock, the “Tx” lock, the “Rx” lock, and the “MII” lock. The MII lock is special in that it blocks device detach using an internal reference count and is frequently required when both the “softc” lock is held or unheld, and two versions are provided that either hold the “softc” lock while increasing or decreasing the reference count, or assume (and in debug builds, assert) the lock is held for the “un_locked” versions.

MII access functions for struct usbnet:

`usbnet_mii_readreg`(dev, phy, reg, valp)
  Read register reg on PHY number phy and return the value in valp. Called with the MII lock held.
`usbnet_mii_writereg`(dev, phy, reg, val)
  Write register reg on PHY number phy with val. Called with the MII lock held.
`usbnet_mii_statchg`(ifp)
  Trigger a status change update for interface ifp. Unlike register access, called with the MII lock not held.

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.

`usbnet_attach`(un, detachname)
  Initial stage attach of a usb network device. The detachname will be used while waiting for final references to drain when detaching.
`usbnet_attach_ifp`(un, if_flags, if_extflags, unm)
  Final stage attach of usb network device. If the passed in unm is non-`NULL` then an MII interface will be created using the values provided in the struct usbnet_mii structure, which has these members passed to `mii_attach`():
  un_mii_flags
    Flags.
  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 and extflags.

`usbnet_detach`(dev, flags)
  Device detach. Usable as actual device method.
`usbnet_activate`(dev, act)
  Device activate (deactivate) method. Usable as actual device method.
`usbnet_stop`(un, ifp, disable)
  Interface stop routine.

# AUTOCONFIGURATION

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 needed.
un_dev
  device_t saved in attach, used for messages mostly.
un_iface
  The USB iface handle for data interactions, see `usbd_device2interface_handle`() for more details.
un_udev
  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 members:
  void `(*uno_stop)`(struct ifnet *ifp, int disable)
    Stop interface (optional.)
  int `(*uno_ioctl)`(struct ifnet *ifp, u_long cmd, void *data)
    Simple ioctl callback (optional.)
  int `(*uno_override_ioctl)`(struct ifnet *ifp, u_long cmd, void *data)
    Full ioctl callback (optional.)
  int `(*uno_init)`(struct ifnet *ifp)
    Initialize (bring up) interface. Required. Must call `usbnet_rx_tx_init`().
  int `(*uno_read_reg)`(struct usbnet *un, int phy, int reg, uint16_t *val)
    Read MII register. Required with MII.
  int `(*uno_write_reg)`(struct usbnet *un, int phy, int reg, uint16_t val)
    Write MII register. Required with MII.
  usbd_status `(*uno_statchg)`(struct ifnet *ifp)
    Handle MII status change. Required with MII.
  unsigned `(*uno_tx_prepare)`(struct usbnet *un, struct mbuf *m, struct usbnet_chain *c)
    Prepare an mbuf for transmit. Required.
  void `(*uno_rx_loop)`(struct usbnet *un, struct usbnet_chain *c, uint32_t total_len)
    Prepare one or more chain for enqueue. Required.
  void `(*uno_intr)`(struct usbnet *un, usbd_status status)
    Process periodic interrupt (optional.)
  void `(*uno_tick)`(struct usbnet *un)
    Called every second with USB task thread context (optional.)
un_intr
  Points to a struct usbnet_intr structure which should have these members set:
  uni_intr_buf
    If non-`NULL`, points to a buffer passed to `usbd_open_pipe_intr`() in the device init callback, along with the size and interval.
  uni_intr_bufsz
    Size of interrupt pipe buffer.
  uni_intr_interval
    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.
un_phyno
  MII phy number. Not used by `usbnet`.
un_eaddr
  6 bytes of Ethernet address that must be provided before calling `usbnet_attach_ifp`() if the device has Ethernet.
un_flags
  Device owned flags word. The `usbnet` framework will not touch this value.
un_rx_xfer_flags
  Passed to `usbd_setup_xfer`() for receiving packets.
un_tx_xfer_flags
  Passed to `usbd_setup_xfer`() for sending packets.
un_rx_list_cnt
  Number of chain elements to allocate for Rx.
un_tx_list_cnt
  Number of chain elements to allocate for Tx.
un_rx_bufsz
  Rx buffer size.
un_tx_bufsz
  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 handling.

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 a the usbnet_cdata and usbnet_chain structures, the `un_ed`, `un_rx_xfer_flags`, and `un_tx_xfer_flags` members, and the `uno_stop`(), `uno_init`(), `uno_tx_prepare`(), and `uno_rx_loop`() callbacks of usbnet_ops.

Typically, the device attach routine will fill in members of the usbnet structure, as listed in AUTOCONFIGURATION. The `un_ed`() member 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 optional `uno_stop`() callback performs device-specific operations to shutdown the transmit or receive handling. `uno_stop`() will be called with the usbnet lock held.

The `uno_init`() callback both performs device-specific enablement and then calls `usbnet_rx_tx_init`(), which sets up the receive, transmit, and, optionally, the interrupt pipes, as well as starting the receive pipes. All USB transfer setup is handled internally to the framework, and 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 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 Rx lock will be held during this call, see `usbnet_lock_rx`() and `usbnet_unlock_rx`().

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 packet. The Tx lock will be held during this call, see `usbnet_lock_tx`() and `usbnet_unlock_tx`().

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 this transfer.

# MII

For devices that have MII support these callbacks in struct usbnet_ops must be provided:

uno_read_reg
  Read an MII register for a particular PHY. Returns standard errno(2).
uno_write_reg
  Write an MII register for a particular PHY. Returns standard errno(2).
uno_statchg
  Handle a status change event for this interface.

The read and write callbacks are called with the MII lock held. See `usbnet_lock_mii`() and `usbnet_unlock_mii`().

# INTERRUPT PIPE

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`() function.) 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:

uni_buf
  Data buffer for interrupt status relies.
uni_bufsz
  Size of the above buffer.
uni_interval
  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:

Headers
  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 rndsource.h, etc.
Device softc
  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, Ethernet address, the ethercom and mii_data structures, end point descriptors, usbd device, interface, and task and callout structures (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, MII, and the base softc lock. There is a driver-only “un_flags” in the usbnet structure available 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.

Interface setup
  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.
Device locking
  The `usbnet` framework provides four locks for the system: normal device/softc lock, receive and transmit locks, and the MII lock. The normal locking order for these locks is ifnet lock -> usbnet lock -> usbnet rxlock -> usbne txlock, or, ifnet lock -> usbnet lock -> MII lock.
MII handling
  For devices with MII support the three normal callbacks (read, write, and status change) must be converted to usbnet. These functions are called with the MII lock is held (see “`usbnet_isowned_mii`()”), and do not require any checking for running, or up, or dying devices unless they drop and retake the MII lock. 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 network 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 upto higher layers. The typical interface “if_start” function and any additional 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 all internal.
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.
Common errors
  It's common to forget to set link active on devices with MII. Be sure to call `usbent_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 no-endpoint value.

# SEE ALSO

usb(4), driver(9), usbd_status(9), usbdi(9)

# HISTORY

This `usbnet` interface first appeared in NetBSD 9.0. Portions of the original design are based upon ideas from Nick Hudson <skrll@NetBSD.org>.

# AUTHORS

Matthew R. Green <mrg@eterna.com.au>

August 22, 2019 | NetBSD 9.5