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

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Message-ID: <496e1153-acac-468a-b39c-9ea138b2cf04@lunn.ch>
Date: Mon, 21 Jul 2025 15:51:07 +0200
From: Andrew Lunn <andrew@...n.ch>
To: yicongsrfy@....com
Cc: oneukum@...e.com, andrew+netdev@...n.ch, davem@...emloft.net,
	netdev@...r.kernel.org, linux-usb@...r.kernel.org,
	Yi Cong <yicong@...inos.cn>
Subject: Re: [PATCH] usbnet: Set duplex status to unknown in the absence of
 MII

On Mon, Jul 21, 2025 at 03:10:22PM +0800, yicongsrfy@....com wrote:
> From: Yi Cong <yicong@...inos.cn>
> 
> CDC device don't use mdio to get link status, duplex is set
> half as default.
> 
> Now cdc_ncm can't get duplex, set it UNKNOWN instead of half
> which might actually be in an error state.

It appears that CDC has a transfer to report the link status:
usbnet_cdc_status(). There is a u32 which contains the link speed. Is
the duplex also included in this transfer?

What does the standard say about duplex? Are 1/2 duplex modes are
supported? Is it clear stated they are not supported? 1G/half not be
supported depending on the MAC/PHY pair?

	Andrew