netdev - Re: [PATCH 1/1] net: phy: marvell: avoid bringing down fibre link when autoneg is bypassed

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Message-ID: <30f9c0d0-499c-47d6-bdf2-a86b6d300dbf@lunn.ch>
Date: Thu, 3 Oct 2024 16:30:19 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Qingtao Cao <qingtao.cao.au@...il.com>
Cc: Qingtao Cao <qingtao.cao@...i.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	"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
Subject: Re: [PATCH 1/1] net: phy: marvell: avoid bringing down fibre link
 when autoneg is bypassed

On Thu, Oct 03, 2024 at 12:25:12PM +1000, Qingtao Cao wrote:
> On 88E151x the SGMII autoneg bypass mode defaults to be enabled. When it is
> activated, the device assumes a link-up status with existing configuration
> in BMCR, avoid bringing down the fibre link in this case
> 
> Test case:
> 1. Two 88E151x connected with SFP, both enable autoneg, link is up with speed
>    1000M
> 2. Disable autoneg on one device and explicitly set its speed to 1000M
> 3. The fibre link can still up with this change, otherwise not.

What is actually wrong here?

If both ends are performing auto-neg, i would expect a link at the
highest speeds both link peers support.

If one peer is doing autoneg, the other not, i expect link down, this
is not a valid configuration, since one peer is going to fail to
auto-neg.

If both peers are using forced 1000M, i would expect a link.

   Andrew