[REGRESSION] e1000e heavy packet loss on Meteor Lake - 6.14.2

["Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>]

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Hi,

After updating to 6.14.2, the ethernet adapter is almost unusable, I get
over 30% packet loss.
Bisect says it's this commit:

    commit 85f6414167da39e0da30bf370f1ecda5a58c6f7b
    Author: Vitaly Lifshits <vitaly.lifshits@intel.com>
    Date:   Thu Mar 13 16:05:56 2025 +0200

        e1000e: change k1 configuration on MTP and later platforms
        
        [ Upstream commit efaaf344bc2917cbfa5997633bc18a05d3aed27f ]
        
        Starting from Meteor Lake, the Kumeran interface between the integrated
        MAC and the I219 PHY works at a different frequency. This causes sporadic
        MDI errors when accessing the PHY, and in rare circumstances could lead
        to packet corruption.
        
        To overcome this, introduce minor changes to the Kumeran idle
        state (K1) parameters during device initialization. Hardware reset
        reverts this configuration, therefore it needs to be applied in a few
        places.
        
        Fixes: cc23f4f0b6b9 ("e1000e: Add support for Meteor Lake")
        Signed-off-by: Vitaly Lifshits <vitaly.lifshits@intel.com>
        Tested-by: Avigail Dahan <avigailx.dahan@intel.com>
        Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
        Signed-off-by: Sasha Levin <sashal@kernel.org>

     drivers/net/ethernet/intel/e1000e/defines.h |  3 ++
     drivers/net/ethernet/intel/e1000e/ich8lan.c | 80 +++++++++++++++++++++++++++--
     drivers/net/ethernet/intel/e1000e/ich8lan.h |  4 ++
     3 files changed, 82 insertions(+), 5 deletions(-)

My system is Novacustom V540TU laptop with Intel Core Ultra 5 125H. And
the e1000e driver is running in a Xen HVM (with PCI passthrough).
Interestingly, I have also another one with Intel Core Ultra 7 155H
where the issue does not happen. I don't see what is different about
network adapter there, they look identical on lspci (but there are
differences about other devices)...

I see the commit above was already backported to other stable branches
too...

#regzbot introduced: 85f6414167da39e0da30bf370f1ecda5a58c6f7b

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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