netdev - Re: [PATCH v2 0/2] Add MHI Endpoint network driver

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Date: Tue, 28 Nov 2023 22:35:50 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>, davem@...emloft.net, 
	edumazet@...gle.com, pabeni@...hat.com, mhi@...ts.linux.dev, 
	linux-arm-msm@...r.kernel.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, loic.poulain@...aro.org
Subject: Re: [PATCH v2 0/2] Add MHI Endpoint network driver

On Mon, 27 Nov 2023 at 18:46, Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Mon, 27 Nov 2023 11:34:39 +0530 Manivannan Sadhasivam wrote:
> > I think you made up your mind that this driver is exposing the network interface
> > to the firmware on the device. I ought to clearify that the device running this
> > driver doesn't necessarily be a modem but a PCIe endpoint instance that uses the
> > netdev exposed by this driver to share data connectivity with another device.
>
> Doesn't matter how many legit use cases you can come up with.
> Using netdev as a device comm channel is something I am
> fundamentally opposed to.
>
> > This concept is not new and being supported by other protocols such as Virtio
> > etc...
>
> Yes. Use virtio, please.

We can try using virtio if we control both sides of the link. However
there are usecases of the upstream Linux running on the modem (PCIe
EP) side and other systems (Win, Android) running on the RC side. In
such cases we have to provide the interface that is expected by the
host driver, which unfortunately is MHI. Not to mention that one of
the PCIe EP regions contains registers which are targeting the MHI
protocol. I am not sure how hardware will react if we bypass this
completely and implement VirtIIO or NTB instead.

Also, please excuse me if this was already answered, just for my understanding:
- If we limit functionality to just networking channels which are used
to pass IP data between host and EP, will that be accepted?

- If we were to implement the PCIe networking card running Linux (e.g.
using Freescale PowerQUICC or Cavium Octeon chips), would you also be
opposed to implementing the EP side of the link as the netdev?

-- 
With best wishes
Dmitry