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

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Message-ID: <20231117070602.GA10361@thinkpad>
Date:   Fri, 17 Nov 2023 12:36:02 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     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

Hi Jakub,

On Thu, Jun 08, 2023 at 06:07:20PM +0530, Manivannan Sadhasivam wrote:
> On Wed, Jun 07, 2023 at 10:43:50AM -0700, Jakub Kicinski wrote:
> > On Wed, 7 Jun 2023 22:41:53 +0530 Manivannan Sadhasivam wrote:
> > > > In any case, I'm opposed to reuse of the networking stack to talk
> > > > to firmware. It's a local device. The networking subsystem doesn't
> > > > have to cater to fake networks. Please carry:
> > > > 
> > > > Nacked-by: Jakub Kicinski <kuba@...nel.org>
> > > > 
> > > > if there are future submissions.  
> > > 
> > > Why shouldn't it be? With this kind of setup one could share the data connectivity
> > > available in the device with the host over IP tunneling. If the IP source in the
> > > device (like modem DSP) has no way to be shared with the host, then those IP
> > > packets could be tunneled through this interface for providing connectivity to
> > > the host.
> > > 
> > > I believe this is a common usecase among the PCIe based wireless endpoint
> > > devices.
> > 
> > We can handwave our way into many scenarios and terrible architectures.
> > I don't see any compelling reason to merge this.
> 
> These kind of usecases exist in the products out there in the market. Regarding
> your comment on "opposed to reuse of the network stack to talk to firmware", it
> not the just the firmware, it is the device in general that is talking to the
> host over this interface. And I don't see how different it is from the host
> perspective.
> 
> And these kind of scenarios exist with all types of interfaces like usb-gadget,
> virtio etc... So not sure why the rule is different for networking subsystem.
> 

Sorry to revive this old thread, this discussion seems to have fell through the
cracks...

As I explained above, other interfaces also expose this kind of functionality
between host and the device. One of the credible usecase with this driver is
sharing the network connectivity available in either host or the device with the
other end.

To make it clear, we have 2 kind of channels exposed by MHI for networking.

1. IP_SW0
2. IP_HW0

IP_SW0 is useful in scenarios I explained above and IP_HW0 is purely used to
provide data connectivity to the host machines with the help of modem IP in the
device. And the host side stack is already well supported in mainline. With the
proposed driver, Linux can run on the device itself and it will give Qcom a
chance to get rid of their proprietary firmware used on the PCIe endpoint
devices like modems, etc...

- Mani

> - Mani
> 
> -- 
> மணிவண்ணன் சதாசிவம்

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