From d9cc0e440f0664f6f3e2c26e39ab9dd5f3badba7 Mon Sep 17 00:00:00 2001 From: Oleksij Rempel Date: Thu, 5 Mar 2026 15:34:28 +0100 Subject: [PATCH] net: usb: lan78xx: skip LTM configuration for LAN7850 Do not configure Latency Tolerance Messaging (LTM) on USB 2.0 hardware. The LAN7850 is a High-Speed (USB 2.0) only device and does not support SuperSpeed features like LTM. Currently, the driver unconditionally attempts to configure LTM registers during initialization. On the LAN7850, these registers do not exist, resulting in writes to invalid or undocumented memory space. This issue was identified during a port to the regmap API with strict register validation enabled. While no functional issues or crashes have been observed from these invalid writes, bypassing LTM initialization on the LAN7850 ensures the driver strictly adheres to the hardware's valid register map. Fixes: 55d7de9de6c3 ("Microchip's LAN7800 family USB 2/3 to 10/100/1000 Ethernet device driver") Cc: stable@vger.kernel.org Signed-off-by: Oleksij Rempel Link: https://patch.msgid.link/20260305143429.530909-4-o.rempel@pengutronix.de Signed-off-by: Jakub Kicinski --- drivers/net/usb/lan78xx.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c index 507dbcf3b7b0..f8558b87eaec 100644 --- a/drivers/net/usb/lan78xx.c +++ b/drivers/net/usb/lan78xx.c @@ -3119,6 +3119,10 @@ static int lan78xx_init_ltm(struct lan78xx_net *dev) int ret; u32 buf; + /* LAN7850 is USB 2.0 and does not support LTM */ + if (dev->chipid == ID_REV_CHIP_ID_7850_) + return 0; + ret = lan78xx_read_reg(dev, USB_CFG1, &buf); if (ret < 0) goto init_ltm_failed; -- 2.47.3