This page gives an overview of the macb driver which is available as part of the Zynq, ZynqMP and Versal Linux distribution and in the mainline.
Paths, files, links and documentation on this page are given relative to the Linux kernel source tree.

HW IP features

• Speed support for 10/100/1000 Mbps
• MAC loopback and PHY loopback
• Partial store and forward option
• Packet buffer option
• Flow control - TX/RX pause
• Checksum offload support, CRC checking, FCS stripping
• Promiscuous mode, Broadcast mode
• Collision detection and enforcement - this is an IP feature, no SW support required
• MDIO support for PHY layer management
• Multicasting support
• VLAN tagged frames
• Half duplex support
• Programmable IPG
• External FIFO interface
• Wake on LAN
• IEEE1588 support for ZynqMP and Versal
• Jumbo frame size support for ZynqMP and Versal
• 64 bit addressing for ZynqMP and Versal
• Priority queue support for ZynqMP and Versal
• PS SGMII support (hardwired to 1Gbps) is present in ZynqMP

Features supported in driver

(Functional HW IP and stack related features)

• Speed support for 10/100/1000 Mbps with clock framework
• Packet buffer option
• Checksum offload support, CRC checking, FCS stripping
• MDIO support for PHY layer management
• Multicasting support
• Programmable IPG
• IEEE1588 support for ZynqMP and Versal
• Jumbo frame size support for ZynqMP and Versal
• 64 bit addressing for ZynqMP and Versal
• Priority queue support for ZynqMP and Versal
• PS SGMII support is present in ZynqMP and supported in the driver
• This driver can be used with PL SGMII/1000BaseX driver on Zynq and ZynqMP
• This driver can be used with gmii2rgmii converter driver
• Support for EthTool queries
• NAPI support
• Clock adaptation on Zynq, ZynqMP and Versal
• Runtime PM and suspend/resume supported on ZynqMP and Versal
• Partial store and forward
• Wake on LAN support using ARP on ZynqMP and Versal

Missing Features, Known Issues and Limitations

• Linux does not support loopback
• Flow control support is not present in the driver. RX pause frames can be received by the IP but TX pause frame support is not provided.
• External FIFO interface is not supported by the driver - this implementation is DMA based.
• No interrupt support for PHY events in driver. The current implementation relies on polling method for phy event
• No IEEE 1588 support for Zynq as the timestamp implementation in IP is not accurate enough.
  • The timestamp generated on a PTP event is stored in a non-latching register. This means that the timestamp is overwritten whenever a PTP event packet arrives. Hence there is no foolproof way to associate a timestamp with the packet.
  • An application using sync, follow up, pdelay request, pdelay response with a sync cycle of 1 second and NO errors in between might possibly work but it is not reliable because sync will fail the moment there is any deviation: i.e. multiple back to back PTP event packets in the same direction (or) a small sync interval on a high traffic system where the SW is unable to process the timestamp register before it is overwritten.
• PS SGMII GT initialization is not supported via zynqmp_phy.c - it needs to be explicitly initialized.
• WOL does not work on warm restart designs because GEM WOL requires an RX BD scratch area that is accessible even during suspend (OCM is used for this) and OCM is secure in this design which is a limitation for this feature.

Important AR links

• WOL does not work on warm restart designs due to some limitations (2018.1/2/3) - AR-71028
• PTP time adjustment for a large negative delta fails in 2018.1/2 - AR-71332
• MACB MDIO bus support - Please find the patches for 2017.1, 2017.2, 2017.3, 2017.4, 2018.1, 2018.2 and 2018.3 at the AR - AR-69132
• ZynqMP PS SGMII GT initialization and related - AR-68866
• ZynqMP PS SGMII fixed link - AR-69769
• TI PHY design on ZynqMP evaluation board has incorrect straps and can be remedied with a SW workaround (already implemented in drivers) - AR-70686
• PL PCS PMA initialization in fsbl for Zynq and ZynqMP - refer to xapp1026 and xapp130
• For custom Versal designs using AIE on 2020.1, make sure the low DDR region is accessible to LPD slaves (including GEM) using a workaround (<link to AR>).
• There is a performance drop of ~100Mbps between 2020.1 (5.4 Linux kernel) and 2019.2 (4.19 Linux kernel) observed on both GEM and Axi Ethernet on Zynq. This is currently suspected to be the result of change in the net framework and there is no workaround yet. Further updates will be documented in AR-75195
• Macb + PL PCS PMA ifconfig down/up may fail without proper reset and clock reinitialization. Please refer to AR-72806.
• For full list of ARs, search XKB

Kernel Configuration

The following config options should be enabled in order to build the macb driver
CONFIG_ETHERNET