Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <1617616369-27305-1-git-send-email-loic.poulain@linaro.org>
 <ddc8cd0fd3212ccbba399b03a059bcf40abbc117.camel@redhat.com> <CAMZdPi_6hCYpiyf4=x1FdA2KHnVg6LFWnfEhCd8PMQP_yFXqCw@mail.gmail.com>
In-Reply-To: <CAMZdPi_6hCYpiyf4=x1FdA2KHnVg6LFWnfEhCd8PMQP_yFXqCw@mail.gmail.com>
From:   Aleksander Morgado <aleksander@aleksander.es>
Date:   Thu, 8 Apr 2021 22:05:49 +0200
Message-ID: <CAAP7ucL8Gc_w=BxFFY50XStJWghmdTWo2W2fdzdJjD3cfuWRRg@mail.gmail.com>
Subject: Re: [PATCH net-next v9 1/2] net: Add a WWAN subsystem
To:     Loic Poulain <loic.poulain@linaro.org>
Cc:     Dan Williams <dcbw@redhat.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jakub Kicinski <kuba@kernel.org>,
        David Miller <davem@davemloft.net>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Hey,

>
> * Note: Userspace tools like ModemManager are able to link control
> ports and netdev by looking at the sysfs hierarchy, it's fine for
> simple connection management, but probably not enough for 'multi PDN'
> support for which devices may have multiple netdev and ports
> targetting different 'PDN contexts'...
>

ModemManager is happy with those devices exposing multiple netdevs
(even connecting different net ports to different contexts/bearers and
such), as long as we can bind all those ports together to the same
"modem device". The sysfs hierarchy has been enough for now for that
purpose; or better said, without the sysfs hierarchy it would not have
worked properly. E.g. there are some drivers out there allowing to
instantiate virtual net ports from a master net port; without proper
links in sysfs to link those virtual net ports to the master net port,
the setup would be extremely unstable.

-- 
Aleksander
https://aleksander.es