netdev - Re: [PATCH v1] net: phy: dp83867: Disable EEE support as not implemented

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Message-ID: <aP-hca4pDsDlEGUt@shell.armlinux.org.uk>
Date: Mon, 27 Oct 2025 16:44:33 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>,
	Emanuele Ghidoli <ghidoliemanuele@...il.com>
Cc: Heiner Kallweit <hkallweit1@...il.com>,
	Emanuele Ghidoli <emanuele.ghidoli@...adex.com>,
	Oleksij Rempel <o.rempel@...gutronix.de>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH v1] net: phy: dp83867: Disable EEE support as not
 implemented

On Mon, Oct 27, 2025 at 04:34:54PM +0100, Emanuele Ghidoli wrote:
> > So, this needs to be tested - please modify phylib's
> > genphy_c45_read_eee_cap1() to print the value read from the register.
> > 
> > If it is 0xffff, that confirms that theory.
> It’s not 0xffff; I verified that the value read is:
> TI DP83867 stmmac-0:02: Reading EEE capabilities from MDIO_PCS_EEE_ABLE: 0x0006

Thanks for testing. So the published manual for this PHY is wrong.
https://www.ti.com/lit/ds/symlink/dp83867ir.pdf page 64.

The comment I quoted from that page implies that the PCS and AN
MMD registers shouldn't be implemented.

Given what we now know, I'd suggest TI PHYs are a mess. Stuff they
say in the documentation that is ignored plainly isn't, and their
PHYs report stuff as capable but their PHYs aren't capable.

I was suggesting to clear phydev->supported_eee, but that won't
work if the MDIO_AN_EEE_ADV register is implemented even as far
as exchanging EEE capabilities with the link partner. We use the
supported_eee bitmap to know whether a register is implemented.
Clearing ->supported_eee will mean we won't write to the advertisement
register. That's risky. Given the brokenness so far, I wouldn't like
to assume that the MDIO_AN_EEE_ADV register contains zero by default.

Calling phy_disable_eee() from .get_features() won't work, because
after we call that method, of_set_phy_eee_broken() will then be
called, which will clear phydev->eee_disabled_modes. I think that is
a mistake. Is there any reason why we would want to clear the
disabled modes? Isn't it already zero? (note that if OF_MDIO is
disabled, or there's no DT node, we don't zero this.)

Your placement is the only possible location as the code currently
stands, but I would like to suggest that of_set_phy_eee_broken()
should _not_ be calling linkmode_zero(modes), and we should be able
to set phydev->eee_disabled_modes in the .get_features() method.

Andrew, would you agree?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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