[PATCH] arm64: dts: rockchip: use MAC TX delay for ROCK 4D

[Sebastian Reichel]

According to the Ethernet controller device tree binding "rgmii-id"
means, that the PCB does not have extra long lines to add the required
delays. This is indeed the case for the ROCK 4D.

The problem is, that the Rockchip MAC Linux driver interprets the
interface type differently and abuses the information to configure
RX and TX delays in the MAC using (vendor) properties 'rx_delay' and
'tx_delay'.

When Detlev Casanova upstreamed the ROCK 4D device tree, he used the
correct description for the board ("rgmii-id"). This results in no delays
being configured in the MAC. At the same time the PHY will provide
some delays.

This works to some degree, but is not a stable configuration. All five
ROCK 4D production boards, which have recently been added to the Collabora
LAVA lab for CI purposes have trouble with data not getting through
after a connection has been established.

Using the same delay setup as the vendor device tree fixes the
functionality (at the cost of not properly following the DT binding).
As we cannot fix the driver behavior for RK3576 (some other boards
already depend on this), let's update the ROCK 4D DT instead.

Signed-off-by: Sebastian Reichel <sebastian.reichel at collabora.com>
---
There is an additional problem, that the link does not come up in the
first place. This has been handled by the recently merged (and less
questionable) DT changes [0] combined with a PHY driver patch to trigger
a PHY reset after the clock has been enabled [1] (I will send a new
version of that patch after this one). Stable network support on the
ROCK 4D requires all patches.

[0] https://lore.kernel.org/linux-rockchip/20250704-rk3576-rock4d-phy-handling-fixes-v1-1-1d64130c4139@kernel.org/
[1] https://lore.kernel.org/netdev/20250704-phy-realtek-clock-fix-v1-1-63b33d204537@kernel.org/
---
 arch/arm64/boot/dts/rockchip/rk3576-rock-4d.dts | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/boot/dts/rockchip/rk3576-rock-4d.dts b/arch/arm64/boot/dts/rockchip/rk3576-rock-4d.dts
index 0388d72076bf79ee4f20ac1d3bc04fe1859f857b..f105ed675d3671e93916c830a9a17dc240ca5fda 100644
--- a/arch/arm64/boot/dts/rockchip/rk3576-rock-4d.dts
+++ b/arch/arm64/boot/dts/rockchip/rk3576-rock-4d.dts
@@ -237,7 +237,7 @@ &cpu_l3 {
 &gmac0 {
 	clock_in_out = "output";
 	phy-handle = <&rgmii_phy0>;
-	phy-mode = "rgmii-id";
+	phy-mode = "rgmii-rxid";
 	pinctrl-names = "default";
 	pinctrl-0 = <&eth0m0_miim
 		     &eth0m0_tx_bus2
@@ -246,6 +246,8 @@ &eth0m0_rgmii_clk
 		     &eth0m0_rgmii_bus
 		     &ethm0_clk0_25m_out>;
 	status = "okay";
+	tx_delay = <0x20>;
+	rx_delay = <0x00>;
 };
 
 &gpu {

---
base-commit: e05818ef75bee755fc56811cb54febf4174d7cf2
change-id: 20250724-rk3576-rock4d-phy-timings-6b4eb4ba82fc

Best regards,
-- 
Sebastian Reichel <sre at kernel.org>