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

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Message-ID: <4f6af874-ca9c-48d5-a812-9fd42226ac5c@ti.com>
Date: Mon, 22 Sep 2025 16:29:05 +0530
From: MD Danish Anwar <danishanwar@...com>
To: Andrew Davis <afd@...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

Hi Andrew

On 17/09/25 10:07 pm, Andrew Davis wrote:
> 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.
> 

virtio-net provides a solution for virtual ethernet interface in a
virtualized environment. Our use-case here is traffic tunneling between
heterogeneous processors in a non virtualized environment such as TI's
AM64x that has Cortex A53 and Cortex R5 where Linux runs on A53 and a
flavour of RTOS on R5(FreeRTOS) and the ethernet controller is managed
by R5 and needs to pass some low priority data to A53. The data plane is
over the shared memory while the control plane is over RPMsg end point
channel.

We had aligned with Andrew L [1] and the ask was to create a generic
Linux Ethernet driver that can be used for heterogeneous system. Similar
to rpmsg_tty.c. It was suggested to create a new rpmsg_eth.c driver that
can be used for this purpose.

Here I have implemented what was suggested in [1]

[1]
https://lore.kernel.org/all/8f5d2448-bfd7-48a5-be12-fb16cdc4de79@lunn.ch/

> 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
> 


-- 
Thanks and Regards,
Danish