netdev - [PATCH v2] usbnet: Set duplex status to unknown in the absence of MII

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Message-Id: <20250724013133.1645142-1-yicongsrfy@163.com>
Date: Thu, 24 Jul 2025 09:31:33 +0800
From: yicongsrfy@....com
To: kuba@...nel.org,
	andrew+netdev@...n.ch,
	andrew@...n.ch,
	oneukum@...e.com
Cc: davem@...emloft.net,
	linux-usb@...r.kernel.org,
	netdev@...r.kernel.org,
	yicong@...inos.cn
Subject: [PATCH v2] usbnet: Set duplex status to unknown in the absence of MII

From: Yi Cong <yicong@...inos.cn>

Currently, USB CDC devices that do not use MDIO to get link status have
their duplex mode set to half-duplex by default. However, since the CDC
specification does not define a duplex status, this can be misleading.

This patch changes the default to DUPLEX_UNKNOWN in the absence of MII,
which more accurately reflects the state of the link and avoids implying
an incorrect or error state.

v2: rewrote commmit messages and code comments

Link: https://lore.kernel.org/all/20250723152151.70a8034b@kernel.org/
Signed-off-by: Yi Cong <yicong@...inos.cn>
---
 drivers/net/usb/usbnet.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 6a3cca104af9..b870e7c6d6a0 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -1013,6 +1013,13 @@ int usbnet_get_link_ksettings_internal(struct net_device *net,
 	else
 		cmd->base.speed = SPEED_UNKNOWN;
 
+	/* The standard "Universal Serial Bus Class Definitions
+	 * for Communications Devices v1.2" does not specify
+	 * anything about duplex status.
+	 * So set it DUPLEX_UNKNOWN instead of default DUPLEX_HALF.
+	 */
+	cmd->base.duplex = DUPLEX_UNKNOWN;
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(usbnet_get_link_ksettings_internal);
-- 
2.25.1