linux-kernel - Re: [PATCH net-next v4 0/7] Add RPMSG Ethernet Driver

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Message-ID: <65a98655-68a1-4bf9-b139-c4172f48dad4@ti.com>
Date: Wed, 17 Sep 2025 11:37:36 -0500
From: Andrew Davis <afd@...com>
To: MD Danish Anwar <danishanwar@...com>,
        "David S. Miller"
	<davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Simon Horman
	<horms@...nel.org>,
        Jonathan Corbet <corbet@....net>, Nishanth Menon
	<nm@...com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Tero Kristo
	<kristo@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski
	<krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Andrew Lunn
	<andrew+netdev@...n.ch>,
        Mengyuan Lou <mengyuanlou@...-swift.com>,
        Lei Wei
	<quic_leiwei@...cinc.com>, Xin Guo <guoxin09@...wei.com>,
        Michael Ellerman
	<mpe@...erman.id.au>, Fan Gong <gongfan1@...wei.com>,
        Lorenzo Bianconi
	<lorenzo@...nel.org>,
        Parthiban Veerasooran
	<Parthiban.Veerasooran@...rochip.com>,
        Lukas Bulwahn
	<lukas.bulwahn@...hat.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>
CC: <netdev@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH net-next v4 0/7] Add RPMSG Ethernet Driver

On 9/17/25 6:44 AM, MD Danish Anwar wrote:
> Hi Andrew,
> 
> On 11/09/25 9:34 pm, Andrew Davis wrote:
>> On 9/11/25 6:36 AM, MD Danish Anwar wrote:
>>> This patch series introduces the RPMSG Ethernet driver, which provides a
>>> virtual Ethernet interface for communication between a host processor and
>>> a remote processor using the RPMSG framework. The driver enables
>>> Ethernet-like packet transmission and reception over shared memory,
>>> facilitating inter-core communication in systems with heterogeneous
>>> processors.
>>>
>>
>> This is neat and all but I have to ask: why? What does this provide
>> that couldn't be done with normal RPMSG messages? Or from a userspace
>> TAP/TUN driver on top of RPMSG?
>>
> 
> This is different from RPMSG because here I am not using RPMSG to do the
> actual TX / RX. RPMSG is only used to share information (tx / rx
> offsets, buffer size, etc) between driver and firmware. The TX / RX
> happens in the shared memory. This implementation uses a shared memory

This is how RPMSG is supposed to be used, it is meant for small messages
and signaling, bulk data should be send out-of-band. We have examples
specifically showing how this should be done when using RPMSG[0], and our
RPMSG backed frameworks do the same (like DSP audio[1] and OpenVX[2]).

> circular buffer with head/tail pointers for efficient data passing
> without copies between cores.
> 
>> This also feels like some odd layering, as RPMSG sits on virtio, and
>> we have virtio-net, couldn't we have a firmware just expose that (or
>> would the firmware be vhost-net..)?
>>
> 
> PMSG sits on virtio, and we do have virtio-net but I am not trying to do
> ethernet communication over RPMSG. RPMSG is only used to exchange
> information between cores regarding the shared memory where the actual
> ethernet communication happens.
> 

Again nothing new here, virtio-net does control plane work though a
message channel but the data plane is done using fast shared memory
vqueues with vhost-net[3]. Using RPMSG would just be an extra unneeded
middle layer and cause you to re-implement what is already done with
virtio-net/vhost-net.

Andrew

[0] https://git.ti.com/cgit/rpmsg/rpmsg_char_zerocopy
[1] https://github.com/TexasInstruments/rpmsg-dma
[2] https://github.com/TexasInstruments/tiovx
[3] https://www.redhat.com/en/blog/deep-dive-virtio-networking-and-vhost-net

>> Andrew
>>
> 
>