netdev - Re: [PATCH] usbnet: Set duplex status to unknown in the absence of MII

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Message-Id: <20250722020933.1221663-1-yicongsrfy@163.com>
Date: Tue, 22 Jul 2025 10:09:33 +0800
From: yicongsrfy@....com
To: andrew@...n.ch
Cc: andrew+netdev@...n.ch,
	davem@...emloft.net,
	linux-usb@...r.kernel.org,
	netdev@...r.kernel.org,
	oneukum@...e.com,
	yicong@...inos.cn
Subject: Re: [PATCH] usbnet: Set duplex status to unknown in the absence of MII

Thanks for your reply!

According to the "Universal Serial Bus Class Definitions for Communications Devices v1.2":
In Section 6.3, which describes notifications such as NetworkConnection and ConnectionSpeedChange,
there is no mention of duplex status.In particular, for ConnectionSpeedChange, its data payload
only contains two 32-bit unsigned integers, corresponding to the uplink and downlink speeds.

Since CDC has no way to obtain the duplex status of the device, ethtool displays a default
value of "Half". I think it would be better to display "unknown" instead of potentially showing
incorrect information — for example, my device is actually operating at 1Gbps Full-duplex,
but ethtool shows 1Gbps Half-duplex.