- Background SoC: RK3568
Ethernet PHY: RTL8211F ×2 (RGMII interface)
MAC ↔ PHY connection: clock_in_out = “input” — the 125 MHz clock is provided from the PHY (CLKOUT) to the SoC.
DTS setting: Both gmac0 and gmac1 use clock_in_out = “input”.
- Issue Summary We’re seeing signal problems on the GMAC0 TXCLK pin (GPIO2_B0).
2.1 Problem Conditions When a 22Ω or 0Ω series resistor is added to TXC,
And we measure the waveform just before it exits the SoC,
The signal swings above an offset (e.g., around +1V ± 0.5V), not around 0V as expected.
Meanwhile, the RXC signal appears normal.
Drive Level Test Results drv_level_1: distorted waveform
From drv_level_5 and higher: waveform becomes normal only without the resistor
If a resistor is connected at TXC, even at drv_level_5, the signal starts swinging above an offset again.
We would appreciate any help or advice to resolve this issue.
Even if you set clock_in_out = "output", it works the same.
dts &gmac0 { assigned-clocks = <&cru SCLK_GMAC0_RX_TX>, <&cru SCLK_GMAC0>; assigned-clock-parents = <&cru SCLK_GMAC0_RGMII_SPEED>, <&gmac0_clkin>; clock_in_out = “input”;
pinctrl-names = "default";
pinctrl-0 = <
&gmac0_miim
&gmac0_tx_bus2
&gmac0_rx_bus2
&gmac0_rgmii_clk
&gmac0_rgmii_bus
&gmac0_clkinout
>;
phy-handle = <&rgmii_phy0>;
phy-mode = "rgmii";
snps,reset-gpio = <&gpio2 RK_PD1 GPIO_ACTIVE_LOW>;
snps,reset-active-low;
/* Reset time is 20ms, 100ms for rtl8211f */
snps,reset-delays-us = <0 20000 100000>;
tx_delay = <0x3c>;
rx_delay = <0x2f>;
status = "okay";
};
&gmac1 { assigned-clocks = <&cru SCLK_GMAC1_RX_TX>, <&cru SCLK_GMAC1>; assigned-clock-parents = <&cru SCLK_GMAC1_RGMII_SPEED>, <&gmac1_clkin>; clock_in_out = “input”;
pinctrl-names = "default";
pinctrl-0 = <
&gmac1m1_miim
&gmac1m1_tx_bus2
&gmac1m1_rx_bus2
&gmac1m1_rgmii_clk
&gmac1m1_rgmii_bus
&gmac1m1_clkinout
>;
phy-handle = <&rgmii_phy1>;
phy-mode = "rgmii";
snps,reset-gpio = <&gpio3 RK_PB0 GPIO_ACTIVE_LOW>;
snps,reset-active-low;
/* Reset time is 20ms, 100ms for rtl8211f */
snps,reset-delays-us = <0 20000 100000>;
tx_delay = <0x4f>;
rx_delay = <0x26>;
status = "okay";
};
&mdio0 { rgmii_phy0: phy@0 { compatible = “ethernet-phy-ieee802.3-c22”; reg = <0x0>; }; };
&mdio1 { rgmii_phy1: phy@0 { compatible = “ethernet-phy-ieee802.3-c22”; reg = <0x0>; }; };
