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Adding Ethernet Support in DTS

Ethernet

Ethernet Support in kernel

  • The kernel has driver for the ethernet controller, which can hook into the TCP/IP stack.

  • There exists PHY driver which would be used by the ethernet driver to get or set the modes and speeds of the connection.

ethernet in linux

Ethernet HW Connectivity

ethernet connectivity

  • The Ethernet’s MAC layer needs to get connected to the Phy layer through Media Independent Interface (MII) for data and Management Data Input/Output (MDIO) for configuration.

  • The phy provides the differential lines to Magnetics isolator, whose output is connected to the RJ-45 Connector.

MII Modes

  • The MII is has more set of lines, which was reduced to half by RMII.

  • MII operates at 2.5 MHZ for 10 Mbps & 25 MHz for 100 Mbps.

  • RMII operates at 50 MHz for 100 Mbps & 10 Mbps, where for 10 Mbps the signals are held for 10 clock cycles.

  • GMII operates as 125 MHz which uses 8 lines for transmission.

Ethernet Controller

  • The target board has SMSC lan91c94 ethernet chipset

  • This ethernet controller has both MAC & PHY integrated within a single chip.

  • The SMSC controller sits on the external bus as memory mapped controller.

  • The memory controller is configured for proper timing and chip select configuration in the boot-loader.

  • The kernel driver would need only the base address and the irq for the controller, which needs to provided by the DTS.

Device Tree Representation for SMSC Ethernet controller

  • Since the ethernet controller is mapped in the memory controller for the address 0x4000300

  • As per the bindings of the smsc controller requires the interrupt number to be specified.

Interrupts from External Device

  • The interrupts can be specified with interrupts-extended property, which takes the interrupt trigger type as one more argument.

  • The interrupt used in Verdex board is a gpio irq, where gpio controller acts as the interrupt parent. Where the #interrupt-cells denotes how many arguments represent a interrupt.

gpio@40{
         .....

         interrupt-controller;
         #interrupt-cells = <0x2>;

         .....
};

DTS for SMSC

  • The dts node can be written as

mac: ethernet@04000300 {
	compatible = "smsc,lan91c94";
	reg = <0x04000300 0xffd00>;
	interrupts-extended = <&gpio 99 IRQ_TYPE_EDGE_RISING>;
};

References for Ethernet Bindings

  • Bindings for smsc is available in Documentation/devicetree/bindings/net/smsc-lan91c111.txt

  • Bindings for generic ethernet controllers is available in Documentation/devicetree/bindings/net/ethernet.txt

Tryout

  • As the board has SMSC based controller connected to the system bus, add node for it to the pxabus node of dts.

  • build the dts

Testing

  • If the SMSC lan controller is added properly to the device tree and the driver is enabled, it should get reflected in the boot log.

  • the ethernet interface can be listed as

$ ifconfig -a

  • the IP address for the interface can be assigned by the kernel using dhcp at the boot, when specified through the kernel boot argument.

  • We can check the kernel command line as

$ cat /proc/cmdline

Testing

  • We can verify the interrupt mapping in

$ cat /proc/interrupts

  • We can check whether interrupts are getting triggered, when packets are sent as

$ ping -c 10.0.2.2
$ cat /proc/interrupts

Enabling SMSC Driver

  • The driver for the SMSC ethernet controller can be enabled in Linux kernel as shown below.

   Device Drivers --->
   	  Network device support --->
	  	  Ethernet driver support --->
		  	    <*>     SMC 91C9x/91C1xxx support