Re: [PATCH v2 00/17] net: introduce Qualcomm IPA driver

From: Johannes Berg
Date: Wed Jun 26 2019 - 13:56:07 EST

On Wed, 2019-06-26 at 08:36 -0500, Alex Elder wrote:
> We need to identify the existence of a WWAN device (which is I
> guess--typically? always?--a modem). Perhaps that can be
> discovered in some cases but I think it means a node described
> by Device Tree.

Yeah, perhaps that's something you could do. I'm not sure though. For
one, for USB devices, obviously it isn't :-) And even for IPA you might
want to support existing DTs I guess.

> So you're saying you have a single Ethernet driver, and it can
> drive an Ethernet device connected to a WWAN, or not connected
> to a WWAN, without any changes. The only distinction is that
> if the device is part of a WWAN it needs to register with the
> WWAN framework. Is that right?

That's what I'm thinking, and I believe (mostly from discussions with
Dan) that this actually exists.

> > > So maybe:
> > > - Hardware probe detects a WWAN device
> > > - The drivers that detect the WWAN device register it with the
> > > WWAN core code.
> > > - A control channel is instantiated at/before the time the WWAN
> > > device is registered
> > > - Something in user space should manage the bring-up of any
> > > other things on the WWAN device thereafter
> >
> > But those things need to actually get connected first :-)
> What I meant is that the registering with the "WWAN core code"
> is what does that "connecting." The WWAN code has the information
> about what got registered. But as I said above, this WWAN device
> needs to be identified, and I think (at least for IPA) that will
> require something in Device Tree. That will "connect" them.
> Or I might be misunderstanding your point.

No, I think we're mostly agreeing, just thinking about different
scenarios. I think for IPA you don't really *need* anything in the DT
though - as soon as the IPA driver is loaded you know for sure you
actually have a modem there, and the IPA driver presumably loads based
on some existing probing (didn't look at it now).

Now, I don't know how the QMI channel to the modem is set up, so of
course you'd want a way of identifying that the two channels (IPA and
QMI) go to the same device and link them together in the WWAN framework.

> > If userspace actually had the ability to create (data) channels, then it
> > would have the ability to also remove them. Right now, this may or may
> > not be supported by the drivers that act together to form the interfaces
> > to a WWAN device.
> I think this (user space control) needs to be an option, but
> it doesn't have to be the only way.