The StarFive VisionFive V1 SBC uses a Motorcomm YT8521 PHY supporting
RGMII-ID, but requires manual adjustment of the RX internal delay to
work properly.

The default RX delay provided by the driver is 1.95 ns, which proves to
be too high. Applying a 50% reduction seems to mitigate the issue.

Also note this adjustment is not necessary on BeagleV Starlight SBC,
which uses a Microchip PHY.  Hence, there is no indication of a
miss-behaviour on the GMAC side, but most likely the issue stems from
the Motorcomm PHY.

Co-developed-by: Emil Renner Berthing <redacted>
Signed-off-by: Emil Renner Berthing <redacted>
Signed-off-by: Cristian Ciocaltea <redacted>
---
 .../boot/dts/starfive/jh7100-starfive-visionfive-v1.dts    | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/riscv/boot/dts/starfive/jh7100-starfive-visionfive-v1.dts b/arch/riscv/boot/dts/starfive/jh7100-starfive-visionfive-v1.dts
index e82af72f1aaf..ca134b9f11bf 100644
--- a/arch/riscv/boot/dts/starfive/jh7100-starfive-visionfive-v1.dts
+++ b/arch/riscv/boot/dts/starfive/jh7100-starfive-visionfive-v1.dts

@@ -18,3 +18,10 @@ gpio-restart {
 		priority = <224>;
 	};
 };
+
+&mdio {
+	phy: ethernet-phy@0 {
+		reg = <0>;
+		rx-internal-delay-ps = <900>;
+	};
+};

-- 
2.43.0