net: libwx: fix VF illegal register access

commit 694de31 upstream.

Register WX_CFG_PORT_ST is a PF restricted register. When a VF is
initialized, attempting to read this register triggers an illegal
register access, which lead to a system hang.

When the device is VF, the bus function ID can be obtained directly from
the PCI_FUNC(pdev->devfn).

Fixes: a04ea57 ("net: libwx: fix device bus LAN ID")
Cc: stable@vger.kernel.org
Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>
Link: https://patch.msgid.link/4D1F4452D21DE107+20260429083743.88961-1-jiawenwu@trustnetic.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Jiawen Wu

drivers/net/ethernet/wangxun/libwx/wx_hw.c

@@ -2480,8 +2480,11 @@ int wx_sw_init(struct wx *wx)
 	wx->oem_svid = pdev->subsystem_vendor;
 	wx->oem_ssid = pdev->subsystem_device;
 	wx->bus.device = PCI_SLOT(pdev->devfn);
-	wx->bus.func = FIELD_GET(WX_CFG_PORT_ST_LANID,
-				 rd32(wx, WX_CFG_PORT_ST));
+	if (pdev->is_virtfn)
+		wx->bus.func = PCI_FUNC(pdev->devfn);
+	else
+		wx->bus.func = FIELD_GET(WX_CFG_PORT_ST_LANID,
+					 rd32(wx, WX_CFG_PORT_ST));
 
 	if (wx->oem_svid == PCI_VENDOR_ID_WANGXUN ||
 	    pdev->is_virtfn) {