[PATCH v4 6/9] riscv: dts: starfive: visionfive-v1: Setup ethernet phy

[Cristian Ciocaltea]

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
misbehaviour on the GMAC side, but most likely the issue stems from
the Motorcomm PHY.

While at it, drop the redundant gpio include, which is already provided
by jh7100-common.dtsi.

Co-developed-by: Emil Renner Berthing <emil.renner.berthing at canonical.com>
Signed-off-by: Emil Renner Berthing <emil.renner.berthing at canonical.com>
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea at collabora.com>
---
 .../jh7100-starfive-visionfive-v1.dts         | 22 ++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

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..4e396f820660 100644
--- a/arch/riscv/boot/dts/starfive/jh7100-starfive-visionfive-v1.dts
+++ b/arch/riscv/boot/dts/starfive/jh7100-starfive-visionfive-v1.dts
@@ -6,7 +6,6 @@
 
 /dts-v1/;
 #include "jh7100-common.dtsi"
-#include <dt-bindings/gpio/gpio.h>
 
 / {
 	model = "StarFive VisionFive V1";
@@ -18,3 +17,24 @@ gpio-restart {
 		priority = <224>;
 	};
 };
+
+/*
+ * The board 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 (1.95ns) is too high, but applying a 50%
+ * reduction seems to mitigate the issue.
+ *
+ * It is worth noting the adjustment is not necessary on BeagleV Starlight SBC,
+ * which uses a Microchip PHY.  Hence, most likely the Motorcomm PHY is the one
+ * responsible for the misbehaviour, not the GMAC.
+ */
+&mdio {
+	phy: ethernet-phy at 0 {
+		reg = <0>;
+		rx-internal-delay-ps = <900>;
+	};
+};
+
+&gmac {
+	phy-handle = <&phy>;
+};
-- 
2.43.0