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

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Date:   Wed, 26 Jun 2019 19:55:48 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Alex Elder <elder@...aro.org>, Dan Williams <dcbw@...hat.com>,
        Arnd Bergmann <arnd@...db.de>
Cc:     Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>,
        abhishek.esse@...il.com, Ben Chan <benchan@...gle.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        cpratapa@...eaurora.org, David Miller <davem@...emloft.net>,
        DTML <devicetree@...r.kernel.org>,
        Eric Caruso <ejcaruso@...gle.com>, evgreen@...omium.org,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-arm-msm@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-soc@...r.kernel.org, Networking <netdev@...r.kernel.org>,
        syadagir@...eaurora.org
Subject: Re: [PATCH v2 00/17] net: introduce Qualcomm IPA driver

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.

Agree.

johannes