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

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Message-ID: <6373678e-d827-4cf7-a98f-e66bda238315@suse.com>
Date: Wed, 23 Jul 2025 09:17:02 +0200
From: Oliver Neukum <oneukum@...e.com>
To: yicongsrfy@....com, 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

On 23.07.25 03:29, yicongsrfy@....com wrote:

> No, the standard does not mention anything about duplex at all.
> 
> However, Chapter 2 of the standard describes the scope of devices
> covered by CDC, including wired and wireless network adapters,
> among others.
> 
> We know that wireless communication is inherently half-duplex;

Well, no. 802.11 is half-duplex. Cell phones are capable of full
duplex. CDC is not just network cards.

> for wired network adapters, the duplex status depends on the
> capabilities of both communication ends.

On ethernet. Again CDC is not limited to ethernet.
  
>  From these two tests, we can conclude that both full-duplex
> and half-duplex modes are supported — the problem is simply
> that the duplex status cannot be retrieved in the absence of
> MII support.

Sort of. You are asking a generic driver to apply a concept
from ethernet. It cannot. Ethernet even if it is half-duplex
is very much symmetrical in speed. Cable modems do not, just
to give an example.

I think we need to centralize the reaction to stuff that is not ethernet.

	Regards
		Oliver