arm64: dts: imx8mn-var-som: fix PHY detection bug by adding deassert delay

commit f161cea5a20f3aeeb637a88ad1705fc2720b4d58 upstream.

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@dimonoff.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/arch/arm64/boot/dts/freescale/imx8mn-var-som.dtsi b/arch/arm64/boot/dts/freescale/imx8mn-var-som.dtsi
index f6287f174355..24f9e8fd0c8b 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 @@
 		#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>;
 		};
 	};
 };