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: <0212f9e8-8f60-461b-a7fe-bd4054f3689b@gmail.com>
Date: Sat, 11 Jan 2025 14:19:04 +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 11:01, Russell King (Oracle) wrote:
> On Sat, Jan 11, 2025 at 10:44:25AM +0100, Heiner Kallweit wrote:
>> 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.
> 
> Ok. Do we at least remove the broken modes from the supported mask
> reported to userspace?
> 
I think that's something we could do in addition, to provide a hint to the
user about unavailable modes. It wouldn't remove the need for the check here.
ethtool doesn't check the advertisement against the supported modes.
And even if it would, we must not rely on input from user space being sane.