[PATCH v2] arm64: dts: imx8mn-var-som: fix PHY detection bug by adding deassert delay

[Hugo Villeneuve]

From: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>

While testing the ethernet interface on a Variscite symphony carrier
board using an imx8mn SOM with an onboard ADIN1300 PHY (EC hardware
configuration), the ethernet PHY is not detected.

The ADIN1300 datasheet indicate that the "Management interface
active (t4)" state is reached at most 5ms after the reset signal is
deasserted.

The device tree in Variscite custom git repository uses the following
property:

    phy-reset-post-delay = <20>;

Add a new MDIO property 'reset-deassert-us' of 20ms to have the same
delay inside the ethphy node. Adding this property fixes the problem
with the PHY detection.

Note that this SOM can also have an Atheros AR8033 PHY. In this case,
a 1ms deassert delay is sufficient. Add a comment to that effect.

Fixes: ade0176dd8a0 ("arm64: dts: imx8mn-var-som: Add Variscite
VAR-SOM-MX8MN System on Module")

Signed-off-by: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
---
 arch/arm64/boot/dts/freescale/imx8mn-var-som.dtsi | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/boot/dts/freescale/imx8mn-var-som.dtsi b/arch/arm64/boot/dts/freescale/imx8mn-var-som.dtsi
index 67072e6c77d5..cbd9d124c80d 100644
--- a/arch/arm64/boot/dts/freescale/imx8mn-var-som.dtsi
+++ b/arch/arm64/boot/dts/freescale/imx8mn-var-som.dtsi
@@ -98,11 +98,17 @@ mdio {
 		#address-cells = <1>;
 		#size-cells = <0>;
 
-		ethphy: ethernet-phy@4 {
+		ethphy: ethernet-phy@4 { /* AR8033 or ADIN1300 */
 			compatible = "ethernet-phy-ieee802.3-c22";
 			reg = <4>;
 			reset-gpios = <&gpio1 9 GPIO_ACTIVE_LOW>;
 			reset-assert-us = <10000>;
+			/*
+			 * Deassert delay:
+			 * ADIN1300 requires 5ms.
+			 * AR8033   requires 1ms.
+			 */
+			reset-deassert-us = <20000>;
 		};
 	};
 };
-- 
2.30.2