linux-kernel - Re: [PATCH] PHY: Fix no autoneg corner case

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Message-ID: <m3ldwyh5yw.fsf@t19.piap.pl>
Date: Mon, 02 Dec 2024 08:57:59 +0100
From: Krzysztof Hałasa <khalasa@...p.pl>
To: Heiner Kallweit <hkallweit1@...il.com>
Cc: Andrew Lunn <andrew@...n.ch>,  netdev <netdev@...r.kernel.org>,  Oliver
 Neukum <oneukum@...e.com>,  Andrew Lunn <andrew+netdev@...n.ch>,  "David
 S. Miller" <davem@...emloft.net>,  Eric Dumazet <edumazet@...gle.com>,
  Jakub Kicinski <kuba@...nel.org>,  Paolo Abeni <pabeni@...hat.com>,
  linux-usb@...r.kernel.org,  linux-kernel@...r.kernel.org,  Jose Ignacio
 Tornos Martinez <jtornosm@...hat.com>,  Ming Lei <ming.lei@...hat.com>
Subject: Re: [PATCH] PHY: Fix no autoneg corner case

Heiner,

Heiner Kallweit <hkallweit1@...il.com> writes:

> If autoneg is supported, then phylib defaults to enable it. I don't see
> anything wrong with this. BaseT modes from 1000Mbps on require autoneg.
> Your original commit message seems to refer to a use case where a certain
> operation mode of the PHY doesn't support autoneg. Then the PHY driver
> should detect this operation mode and clear the autoneg-supported bit.

I'm not sure about it, but if there is consensus it should stay this
way, no problem.

WRT specific case, It seems the SFP port doesn't support autoneg on
AX88772BL (I don't have any SFP copper 10/100 module).

The PHY registers (100BASE-FX, no link currently):
          x0   x1   x2   x3   x4   x5   x6   x7   x8
  0000: 2100 7809   3B 1881  501
  0010:  250  80C 8620   20 2314  3C8 4716 724F 8024

BMCR: fixed speed 100 Mb/s
      The datasheet says "autoneg is fixed to 1 and speed to 100", but
      it's apparently the case only with 100BASE-TX, not FX.

      It seems autoneg, speed and duplex bits are read only
      (bits 13, 12, 9, 8). So, basically, you can't enable autoneg at
      all and this is maybe the source of the "bug".

BMSR: 10 and 100 Mb/s FD/HD autoneg support indicated. Hmm. R/O.

ANAR: quite standard, but doesn't matter since autoneg is disabled.

I will think about it a bit more.
-- 
Krzysztof "Chris" Hałasa

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