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Function and Usage of K1 GMAC

For the GMAC dts configuration, it is necessary to determine the pin group used by the Ethernet, the phy reset gpio, the phy model and address. The tx phase and rx phase generally use the default values.

pinctrl​

Check the schematic diagram of the development board to find the pin group used by the gmac. Suppose eth0 uses the pin group of GPIO00~GPIO14, GPIO45, and the configuration can adopt the configuration of the pinctrl_gmac0 group in k1 - x_pinctrl.dtsi. The eth0 in the solution dts uses the gmac0 pinctrl as follows:

&eth0 {
    pinctrl - names = "default";
    pinctrl - 0 = <&pinctrl_gmac0>;
};

gpio​

Check the schematic diagram of the development board to find the gpio of the Ethernet phy reset signal. Suppose the phy reset gpio of eth0 is gpio 110. The eth0 in the solution dts uses gpio 110 as follows.

&eth0 {
    emac, reset - gpio = <&gpio 110 0>;

phy Configuration​

phy Identification​

Check the schematic diagram of the development board to confirm the model and phy id of the Ethernet phy. For example, the Ethernet phy RTL8821F - CG has a phy id of 001c.c916. The phy id information can be found in the phy spec or provided by contacting the phy manufacturer.

phy Address​

Check the schematic diagram of the development board to confirm the address of the Ethernet phy. Suppose it is 1.

phy Configuration​

According to the phy identification id and phy address obtained in 5.3.1 and 5.3.2, configure the phy. The eth0 configuration in the solution dts is as follows:

&eth0 {
   ...
    mdio - bus {
                #address - cells = <0x1>;
                #size - cells = <0x0>;
                rgmii0: phy@0 {
                        compatible = "ethernet - phy - id001c.c916";
                        device_type = "ethernet - phy";
                        reg = <0x1>;
                        phy - mode = "rgmii";
                };
    };
};

tx phase and rx phase​

The default value of tx - phase is 90, and the default value of rx - phase is 73. The tx - phase and rx - phase may need to be adjusted for different boards. If the eth0 port can be up, but cannot be assigned an IP address, you need to contact Spacemit to adjust the tx - phase and rx - phase.

&eth0 {
    tx - phase = <90>;
    rx - phase = <73>;
};

dts Configuration​

Based on the Ethernet hardware information of the development board, the configuration is as follows.

&eth0 {
        pinctrl - names = "default";
        pinctrl - 0 = <&pinctrl_gmac0>;
        emac, reset - gpio = <&gpio 110 0>;
        emac, reset - active - low;
        emac, reset - delays - us = <0 10000 100000>;
        /* store forward mode */
        tx - threshold = <1518>;
        rx - threshold = <12>;
        tx - ring - num = <128>;
        rx - ring - num = <128>;
        dma - burst - len = <5>;
        ref - clock - from - phy;
        clk - tuning - enable;
        clk - tuning - by - delayline;
        tx - phase = <90>;
        rx - phase = <73>;
        phy - handle = <&rgmii0>;
        status = "okay";
        mdio - bus {
                #address - cells = <0x1>;
                #size - cells = <0x0>;
                rgmii0: phy@0 {
                        compatible = "ethernet - phy - id001c.c916";
                        device_type = "ethernet - phy";
                        reg = <0x1>;
                        phy - mode = "rgmii";
                };
        };
};