On Wed, 2020-06-17 at 18:48 +0200, Andrew Lunn wrote: > On Wed, Jun 17, 2020 at 03:21:53PM +0200, Tanjeff-Nicolai Moos wrote: > > Hi netdevs, > > > > Kernel version: > > > > I'm working with kernel 4.14.137 (OpenWRT project). But I looked > > at > > the source of kernel 5.7 and found the same situation. > > > > Problem: > > > > I'm using the qmi_wwan driver for a Sierra Wireless EM7455 LTE > > modem. This driver does not use > > netif_carrier_on()/netif_carrier_off() to update its link status. > > This confuses ledtrig_netdev which uses netif_carrier_ok() to > > obtain > > the link status. > > > > My solution: > > > > As a solution (or workaround?) I would try: > > > > 1) In drivers/net/usb/qmi_wwan.c, lines 904/913: Add the flag > > FLAG_LINK_INTR. > > > > 2) In drivers/net/usb/usbnet.c, functions usbnet_open() and > > usbnet_stop(): Add a call to netif_carrier_*(), > > but only if FLAG_LINK_INTR is set. > > > > Question: > > > > Is this the intended way to use FLAG_LINK_INTR and > > netif_carrier_*()? > > Or is there another recommended way to obtain the link status of > > network devices (I could change ledtrig_netdev)? > > Hi Tanjeff > > With Ethernet, having a carrier means there is a link partner, the > layer 2 of the OSI 7 layer stack model is working. If the interface > is > not open()ed, it clearly should not have carrier. However, just > because it is open, does not mean it has carrier. The cable could be > unplugged, etc. > > This is an LTE modem. What does carrier mean here? I don't know if it > is well defined, but i would guess it is connected to a base station > which is offering service. I'm assuming you are interested in data > here, not wanting to make a 911/999/112/$EMERGENCY_SERVICE call which > in theory all base stations should accept. > > Is there a way to get this state information from the hardware? That > would be the correct way to set the carrier.
There isn't. All the setup that would result in IFF_LOWER_UP (eg ability to pass packets to the cellular network) happens over channels *other* than the ethernet one. eg CDC-WDM, CDC-ACM, CDC-MBIM, AT commands, QMI commands, MBIM commands, etc. Something in userspace handles the actual IP-level connection setup and once that's done, only then do you really have IFF_LOWER_UP. One way to solve this could be to require userspace connection managers to manage the carrier state of the device, which is possible for some drivers already IIRC. Dan
