From: Andrew Lunn <andrew@lunn.ch>
To: Petr Machata <petrm@mellanox.com>
Cc: Amit Cohen <amitc@mellanox.com>, mlxsw <mlxsw@mellanox.com>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"o.rempel@pengutronix.de" <o.rempel@pengutronix.de>
Subject: Re: Link down reasons
Date: Thu, 28 May 2020 17:40:10 +0200 [thread overview]
Message-ID: <20200528154010.GD840827@lunn.ch> (raw)
In-Reply-To: <87zh9stocb.fsf@mellanox.com>
> Andrew, pardon my ignorance in these matters, can a PHY driver in
> general determine that the issue is with the cable, even without running
> the fairly expensive cable test?
No. To diagnose a problem, you need the link to be idle. If the link
peer is sending frames, they interfere with TDR. So all the cable
testing i've seen first manipulates the auto-negotiation to make the
link peer go quiet. That takes 1 1/2 seconds. There are some
optimizations possible, e.g. if the cable is so broken it never
establishes link, you can skip this. But Ethernet tends to be robust,
it drops back to 100Mbps only using two pairs if one of the four pairs
is broken, for example.
Andrew
next prev parent reply other threads:[~2020-05-28 15:40 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <AM0PR0502MB38261D4F4F7A3BB5E0FDCD10D7B10@AM0PR0502MB3826.eurprd05.prod.outlook.com>
2020-05-27 21:38 ` Link down reasons Andrew Lunn
2020-05-28 5:56 ` Amit Cohen
2020-05-28 9:12 ` Petr Machata
2020-05-28 15:40 ` Andrew Lunn [this message]
2020-05-28 16:54 ` Petr Machata
2020-05-28 17:17 ` Michal Kubecek
2020-05-28 18:37 ` Andrew Lunn
2020-05-29 9:03 ` Petr Machata
2020-05-28 8:40 ` Oleksij Rempel
2020-05-28 9:22 ` Petr Machata
2020-05-28 10:28 ` Oleksij Rempel
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