linux-kernel - Re: [PATCH net-next v4 0/4] usbnet: speed reporting for devices without MDIO

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Date:   Wed, 07 Apr 2021 13:36:43 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Grant Grundler <grundler@...omium.org>,
        Andrew Lunn <andrew@...n.ch>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Roland Dreier <roland@...nel.org>,
        nic_swsd <nic_swsd@...ltek.com>, netdev <netdev@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v4 0/4] usbnet: speed reporting for devices
 without MDIO

Am Dienstag, den 06.04.2021, 18:01 +0000 schrieb Grant Grundler:

> > Ethernet does not support
> > different rates in each direction. So if RX and TX are different, i
> > would actually say something is broken.
> 
> Agreed. The question is: Is there data or some heuristics we can use
> to determine if the physical layer/link is ethernet?
> I'm pessimistic we will be able to since this is at odds with the
> intent of the CDC spec.

Yes, CDC intends to hide that. We can conclude that an asymmetric link
rules out ethernet, but anything else is difficult.

	Regards
		Oliver