netdev - Re: [PATCH net-next 3/9] net: phy: c45: don't accept disabled EEE modes in genphy_c45_ethtool_set

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Message-ID: <472f6fe4-18ff-4124-ba43-fd757df7cb4d@gmail.com>
Date: Sat, 11 Jan 2025 10:44:25 +0100
From: Heiner Kallweit <hkallweit1@...il.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Paolo Abeni <pabeni@...hat.com>, Jakub Kicinski <kuba@...nel.org>,
 David Miller <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Simon Horman <horms@...nel.org>, Andrew Lunn <andrew@...n.ch>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 3/9] net: phy: c45: don't accept disabled EEE
 modes in genphy_c45_ethtool_set_eee

On 11.01.2025 10:21, Russell King (Oracle) wrote:
> On Sat, Jan 11, 2025 at 10:06:02AM +0100, Heiner Kallweit wrote:
>> Link modes in phydev->eee_disabled_modes are filtered out by
>> genphy_c45_write_eee_adv() and won't be advertised. Therefore
>> don't accept such modes from userspace.
> 
> Why do we need this? Surely if the MAC doesn't support modes, then they
> should be filtered out of phydev->supported_eee so that userspace knows
> that the mode is not supported by the network interface as a whole, just
> like we do for phydev->supported.
> 
> That would give us the checking here.
> 
Removing EEE modes to be disabled from supported_eee is problematic
because of how genphy_c45_write_eee_adv() works.

Let's say we have a 2.5Gbps PHY and want to disable EEE at 2.5Gbps. If we
remove 2.5Gbps from supported_eee, then the following check is false:
if (linkmode_intersects(phydev->supported_eee, PHY_EEE_CAP2_FEATURES))
What would result in the 2.5Gbps mode not getting disabled.