[PATCH] arm64: dts: imx8mp-debix-model-a: Disable EEE for 1000T

[Laurent Pinchart]

Energy Efficient Ethernet (EEE) is broken at least for 1000T on the EQOS
(DWMAC) interface. When connected to an EEE-enabled peer, the ethernet
devices produces an interrupts storm. Disable EEE support to fix it.

Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
The exact reason for the interrupt storm is unknown, and my attempts to
diagnose it was hindered by my lack of expertise with DWMAC. As far as I
understand, the DWMAC implements EEE support, and so does the RTL8211E
PHY according to its datasheet. What each side does exactly is unknown
to me. One theory I've heard to explain the issue is that the two
implementations conflict. There is no register in the RTL8211E PHY to
disable EEE on the PHY side while still advertising its support to the
peer and relying on the implementation in the DWMAC (if this even makes
sense), so disabling EEE is the only viable option.

This patch is likely a workaround, but it fixes ethernet usage on the
board, so it's in my opinion worth being merged. If someone with better
knowledge of EEE and DWMAC, as well as an interest in getting it working
properly on the Debix board, wants to submit additional patches to drop
eee-broken-1000t, I will be happy to test them.
---
 arch/arm64/boot/dts/freescale/imx8mp-debix-model-a.dts | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/boot/dts/freescale/imx8mp-debix-model-a.dts b/arch/arm64/boot/dts/freescale/imx8mp-debix-model-a.dts
index 9422beee30b2..4aa47f71425b 100644
--- a/arch/arm64/boot/dts/freescale/imx8mp-debix-model-a.dts
+++ b/arch/arm64/boot/dts/freescale/imx8mp-debix-model-a.dts
@@ -102,6 +102,7 @@ ethphy0: ethernet-phy at 1 { /* RTL8211E */
 			reset-gpios = <&gpio4 18 GPIO_ACTIVE_LOW>;
 			reset-assert-us = <20>;
 			reset-deassert-us = <200000>;
+			eee-broken-1000t;
 		};
 	};
 };
-- 
Regards,

Laurent Pinchart