Subject: Re: [PATCH v2] ARM: multi_v7_defconfig: Enable CONFIG_RPMSG_TTY
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC:     Russell King <linux@armlinux.org.uk>,
        Arnd Bergmann <arnd@arndb.de>, Joel Stanley <joel@jms.id.au>,
        Dmitry Osipenko <digetx@gmail.com>,
        Thierry Reding <treding@nvidia.com>,
        Manivannan Sadhasivam <mani@kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>
References: <20211220161155.32564-1-arnaud.pouliquen@foss.st.com>
 <YcC2M/QseKewXDGw@kroah.com>
From:   Arnaud POULIQUEN <arnaud.pouliquen@foss.st.com>
Message-ID: <214788db-6774-5501-bc12-67d3135b50ec@foss.st.com>
Date:   Tue, 21 Dec 2021 10:05:56 +0100
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On 12/20/21 5:58 PM, Greg Kroah-Hartman wrote:
> On Mon, Dec 20, 2021 at 05:11:55PM +0100, Arnaud Pouliquen wrote:
>> The RPMsg TTY implements an inter-processor communication with a standard
>> TTY interface on top of the RPMsg framework.
>> This driver is a generic RPMsg client that can run on different platforms.
>>
>> By enabling the RPMSG_TTY driver as module in multi_v7_defconfig, it makes
>> possible to automatically probe the rpmsg_tty driver by the RPMsg bus,
>> when the support of the RPMsg service is dynamically requested by the
>> co-processor firmware.
>>
>> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
>> ---
>> delta vs V1:
>> add
>> ---
> 
> "add"?  What does that mean?

Oops, sorry, part of my sentence has disappeared
"Add more description in commit message to detail the objective ".

> 
> Do all v7 chips have this hardware?

I would say yes and no

No - As mainly used today for hardware system integrating a main and a
coprocessor in a single chip.

Yes - as that depends on the RPMsg back-end

The RPMsg is divided in 3 layers
 - the service layer that implement a service on top of the RPmsg
	A parallel could be done between this layer and the Virtio devices such
	as the "Virtio-Console".
	=> the rpmsg _tty is part of this layer
	=> rpmsg_char is another one ( already enabled in some configs)

 - the transport layer in charge of the RPmsg protocol
 - the back-end layer that is the hardware abstraction layer
	- The main back-end used is the RPMsg VirtIO back-end which implements
	  the RPMSg over VirtIO.
	- There are also some platform specific backends (e.g. QCOM, MediaTek)
	- We have also some demos that implement the RPMsg protocol on top of a
	  serial link back-end allowing communication with an external
	  processor. Not up-streamed yet.

Thanks,
Arnaud

> 
> thanks,
> 
> greg k-h
>