Hi,
In our custom board based on IMX8MN, we are facing issue in RMII Ethernet interface.
Below is the device tree configuration.
pinctrl_fec1: fec1grp {
fsl,pins = <
MX8MN_IOMUXC_ENET_MDC_ENET1_MDC 0x3
MX8MN_IOMUXC_ENET_MDIO_ENET1_MDIO 0x23
MX8MN_IOMUXC_ENET_TXC_ENET1_RGMII_TXC 0x4000001f
MX8MN_IOMUXC_ENET_TD1_ENET1_RGMII_TD1 0x56
MX8MN_IOMUXC_ENET_TD0_ENET1_RGMII_TD0 0x56
MX8MN_IOMUXC_ENET_RD1_ENET1_RGMII_RD1 0x56
MX8MN_IOMUXC_ENET_RD0_ENET1_RGMII_RD0 0x56
MX8MN_IOMUXC_ENET_RXC_ENET1_RX_ER 0x56
MX8MN_IOMUXC_ENET_RX_CTL_ENET1_RGMII_RX_CTL 0x56
MX8MN_IOMUXC_ENET_TX_CTL_ENET1_RGMII_TX_CTL 0x56
MX8MN_IOMUXC_ENET_RD2_GPIO1_IO28 0x19 /* Interrupt */
MX8MN_IOMUXC_GPIO1_IO00_GPIO1_IO0 0x116 /* Reset */
>;
};
&fec1 {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_fec1>;
phy-mode = "rmii";
phy-handle = <ðphy0>;
phy-reset-gpios = <&gpio1 0 GPIO_ACTIVE_LOW>;
fsl,magic-packet;
status = "okay";
mdio {
#address-cells = <1>;
#size-cells = <0>;
ethphy0: ethernet-phy@0 {
compatible = "ethernet-phy-ieee802.3-c22";
reg = <0>;
interrupt-parent = <&gpio1>;
interrupts = <28 IRQ_TYPE_EDGE_FALLING>;
};
};
};
After booting, we are able to see Ethernet driver log
[ 6.069688] Micrel KSZ8081 or KSZ8091 30be0000.ethernet-1:00: attached PHY driver [Micrel KSZ8081 or KSZ8091] (mii_bus:phy_addr=30be0000.ethernet-1:00, irq=77)
But when we connect Ethernet cable to the board, the link is not getting detected. I found one reference dts imx8mq-ddr3l-val.dts, where a RMII interface has been configured.
pinctrl_fec1: fec1grp {
fsl,pins = <
MX8MQ_IOMUXC_ENET_MDC_ENET1_MDC 0x3
MX8MQ_IOMUXC_ENET_MDIO_ENET1_MDIO 0x23
MX8MQ_IOMUXC_ENET_TD2_ENET1_TX_CLK 0x4000001f
MX8MQ_IOMUXC_ENET_TD1_ENET1_RGMII_TD1 0x56
MX8MQ_IOMUXC_ENET_TD0_ENET1_RGMII_TD0 0x56
MX8MQ_IOMUXC_ENET_RD1_ENET1_RGMII_RD1 0x56
MX8MQ_IOMUXC_ENET_RD0_ENET1_RGMII_RD0 0x56
MX8MQ_IOMUXC_ENET_RXC_ENET1_RX_ER 0x56
MX8MQ_IOMUXC_ENET_RX_CTL_ENET1_RGMII_RX_CTL 0x56
MX8MQ_IOMUXC_ENET_TX_CTL_ENET1_RGMII_TX_CTL 0x56
>;
};
In the above pin mux configuration it uses MX8MQ_IOMUXC_ENET_TD2_ENET1_TX_CLK, but we are using MX8MN_IOMUXC_ENET_TXC_ENET1_RGMII_TXC.
Whether ENET1_TX_CLK and ENET1_RGMII_TXC are same..? Will it cause a problem in link detection.
Below is our custom board RMII ethernet connection schematic. 
