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

[Laurent Pinchart]

Hi Russell,

On Mon, Oct 27, 2025 at 09:07:32AM +0000, Russell King (Oracle) wrote:
> On Sun, Oct 26, 2025 at 02:29:04PM +0200, Laurent Pinchart wrote:
> > 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.
> 
> As this is the second problem that has been reported recently, please
> bisect the conversion of stmmac to phylink managed EEE support and see
> whether there is anything in that which is causing this.

Emanuele Ghidoli has bisected this to commit 2c81f3357136 ("net: stmmac:
convert to phylink PCS support"), as reported in [1]. I can test that
commit and the commit just before tonight.

[1] https://lore.kernel.org/all/341f56de-9dde-4c44-9542-b523e1917dcb@gmail.com/

> Please also confirm that EEE was enabled (as soon through ethtool)
> prior to stmmac's conversion (I believe it was due to this code that
> was present in stmmac_init_phy():
> 
> -               if (priv->dma_cap.eee)
> -                       phy_support_eee(phydev);
> -
>                 ret = phylink_connect_phy(priv->phylink, phydev);
> 
> > 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.
> 
> The changes to stmmac have been tested on nVidia Jetson Xavier NX,
> which uses RGMII with dwmac4 and a RTL8211F PHY, connected to a Netgear
> GS108 switch. It seems to be the same that your board is using similar.

Very similar indeed, with a RTL8211E instead of the RTL8211F.

> I will re-test today.

Thank you.

-- 
Regards,

Laurent Pinchart