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

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Message-ID: <CAK8P3a3r95gXMdq7s9GF=37v6t4kR+-2iyC6bnmUDVuM+bn80Q@mail.gmail.com>
Date:   Tue, 18 Jun 2019 23:06:29 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     Alex Elder <elder@...aro.org>, Dan Williams <dcbw@...hat.com>,
        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 Tue, Jun 18, 2019 at 10:39 PM Johannes Berg
<johannes@...solutions.net> 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.

      Arnd