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SubjectRe: [PATCH v2 00/17] net: introduce Qualcomm IPA driver
On Tue, 2019-06-18 at 23:06 +0200, Arnd Bergmann wrote:
> On Tue, Jun 18, 2019 at 10:39 PM Johannes Berg
> <> wrote:
> > On Tue, 2019-06-18 at 22:33 +0200, Arnd Bergmann wrote:
> > It seems to me though that this is far more complex than what I'm
> > proposing? What I'm proposing there doesn't even need any userspace
> > involvement, as long as all the pieces are in the different sub-
> > drivers,
> > they'd fall out automatically.
> >
> > And realistically, the wwan_device falls out anyway at some point,
> > the
> > only question is if we really make one specific driver be the
> > "owner" of
> > it. I'm suggesting that we don't, and just make its lifetime depend
> > on
> > the links to parts it has (unless something like IPA actually wants
> > to
> > be an owner).
> My feeling so far is that having the wwan_device be owned by a device
> gives a nicer abstraction model that is also simpler for the common
> case. A device driver like ipa would end up with a probe() function
> that does does wwan_device_alloc/wwan_device_register, corresponding
> to alloc_etherdev/register_netdev, and then communicates through
> callbacks.
> I agree the compound device case would get more complex by
> shoehorning it into this model, but that can be a valid tradeoff
> if it's the exceptional case rather than the common one.

In my experience, the compound device model is by far the most
prevalent for regular Linux distros or anything *not* running on an SoC
with an integrated modem.

But it's also quite common for Android, no? drivers/net/ethernet/msm/
has rmnet and IPA ethernet drivers while arch/arm/mach-msm/ has various
SMD-related control channel drivers like smd_tty.c and smd_qmi.c and
smd_nmea.c. At least that's how I remember older SMD-based devices
being in the 8xxx and 9xxx time.

Ideally those setups can benefit from this framework as well, without
having to write entirely new composite drivers for those devices.


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