On Tue, 2019-06-04 at 22:04 +0200, Arnd Bergmann wrote: > On Tue, Jun 4, 2019 at 5:18 PM Dan Williams <dcbw@xxxxxxxxxx> wrote: > > On Tue, 2019-06-04 at 10:13 +0200, Arnd Bergmann wrote: > > > Can you describe what kind of multiplexing is actually going on? > > > I'm still unclear about what we actually use multiple logical > > > interfaces for here, and how they relate to one another. > > > > Each logical interface represents a different "connection" (PDP/EPS > > context) to the provider network with a distinct IP address and > > QoS. > > VLANs may be a suitable analogy but here they are L3+QoS. > > > > In realistic example the main interface (say rmnet0) would be used > > for > > web browsing and have best-effort QoS. A second interface (say > > rmnet1) > > would be used for VOIP and have certain QoS guarantees from both > > the > > modem and the network itself. > > > > QMAP can also aggregate frames for a given channel > > (connection/EPS/PDP > > context/rmnet interface/etc) to better support LTE speeds. > > Thanks, that's a very helpful explanation! > > Is it correct to say then that the concept of having those separate > connections would be required for any proper LTE modem > implementation, > but the QMAP protocol (and based on that, the rmnet implementation) > is Qualcomm specific and shared only among several generations of > modems from that one vendor? Exactly correct. This is what Johannes is discussing in his "cellular modem APIs - take 2" thread about how this should all be organized at the driver level and I think we should figure that out before we commit to IPA-with-a-useless-netdev that requires rmnets to be created on top. That may end up being the solution but let's have that discussion. > > You mentioned the need to have a common user space interface > for configuration, and if the above is true, I agree that we should > try > to achieve that, either by ensuring rmnet is generic enough to > cover other vendors (and non-QMAP clients), or by creating a > new user level interface that IPA/rmnet can be adapted to. I would not suggest making rmnet generic; it's pretty QMAP specific (but QMAP is spoken by many many modems both SoC, USB stick, and PCIe minicard). Instead, I think what Johannes is discussing is a better approach. A kernel WWAN framework with consistent user API that rmnet/IPA/qmi_wwan/MBIM/QMI/serial/Sierra can all implement. That wouldn't affect the core packet processing of IPA/rmnet but instead: 1) when/how an rmnet device actually gets created on top of the IPA (or qmi_wwan) device AND (one of these two) a) whether IPA creates a netdev on probe OR b) whether there is some "WWAN device" kernel object which userspace interacts with create rmnet channels on top of IPA Dan
