GENET(4)

NAME
genet - Raspberry Pi 4 / BCM2711 Gigabit Ethernet controller driver

SYNOPSIS
To compile this driver into the kernel, place the following lines in the kernel configuration file:

device miibus
device genet

DESCRIPTION
The genet driver supports the BCM2711 Ethernet controller as found on the Raspberry Pi 4.

The following features are supported in the genet driver in FreeBSD:

IP/TCP/UDP checksum offload for IPv4 and IPv6
10/100/1000Mbps operation in full-duplex mode
10/100Mbps operation in half-duplex mode

Note that the operation of transmit checksum offload is coupled for IPv4 and IPv6; to disable it, both must be disabled even if both address families are not in use.

The genet driver supports the following media types:

autoselect
    Enable autoselection of the media type and options. The user can manually override the autoselected mode by adding media options to rc.conf(5).

10baseT/UTP
    Set 10Mbps operation. The ifconfig(8) mediaopt option can also be used to select either full-duplex or half-duplex modes.

100baseTX
    Set 100Mbps (Fast Ethernet) operation. The ifconfig(8) mediaopt option can also be used to select either full-duplex or half-duplex modes.

1000baseT
    Set 1000baseT operation over twisted pair. Only full-duplex mode is supported.

The genet driver supports the following media options set with the mediaopt option to the ifconfig(8) command:

full-duplex
    Force full duplex operation.

half-duplex
    Force half duplex operation.

For more information on configuring this device, see ifconfig(8).

HARDWARE
The genet driver supports the Ethernet controller portion of the Broadcom BCM2711 on the Raspberry Pi 4 Model B and related systems. It utilizes the BCM54213PE PHY.

LOADER TUNABLES
Tunables can be set at the loader(8) prompt before booting the kernel or stored in loader.conf(5). The following loader tunable variable is available, and is also available as a read-only sysctl(8) variable:

hw.genet.rx_batch
    The maximum number of packets to pass to the link-layer input routine at one time. The default is 16.

SYSCTL VARIABLES
The following variable is available as a sysctl(8) variable:

hw.genet.tx_hdr_min
    When the driver is given an output packet in a buffer chain in which the first buffer contains only the Ethernet header, the number of bytes of the packet to add to the Ethernet header in the first buffer. Certain packets may be lost if this value is too small. The default value is 56, and is sufficient for the observed cases to date.

DIAGNOSTICS
The genet driver has no diagnostics that are likely in normal operation. However, when the debug option is set with ifconfig(8), most failures that cause packet loss in the transmit and receive paths cause a cryptic diagnostic message naming the failure. These messages generally make sense only when looking at the driver source.

SEE ALSO
altq(4), arp(4), miibus(4), netintro(4), ng_ether(4), vlan(4), ifconfig(8)

HISTORY
The genet device driver first appeared in FreeBSD 13.0.

AUTHORS
The genet driver was written by Mike Karels <karels@freebsd.org>. Portions are derived from the bcmgenet driver in NetBSD by Jared McNeill, and parts of the structure and common code are from the awg driver for the Allwinner EMAC by Jared McNeill.