linux-kernel - Re: [RFC PATCH 00/13] can: slcan: extend supported features

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Message-ID: <20220608015521.1ad4853c.max@enpas.org>
Date:   Wed, 8 Jun 2022 01:55:21 +0200
From:   Max Staudt <max@...as.org>
To:     Vincent MAILHOL <mailhol.vincent@...adoo.fr>
Cc:     Dario Binacchi <dario.binacchi@...rulasolutions.com>,
        linux-kernel@...r.kernel.org,
        Amarula patchwork <linux-amarula@...rulasolutions.com>,
        michael@...rulasolutions.com,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        Paolo Abeni <pabeni@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [RFC PATCH 00/13] can: slcan: extend supported features

On Tue, 7 Jun 2022 21:19:54 +0900
Vincent MAILHOL <mailhol.vincent@...adoo.fr> wrote:

> In his CAN327 driver, Max manages to bring the can0 device without the
> need of dedicated user space daemon by using line discipline
> (ldattach):
> https://lore.kernel.org/linux-can/20220602213544.68273-1-max@enpas.org/
> 
> Isn't the same feasible with slcan so that we completely remove the
> dependency toward slcand?
> Max what do you think of this?

I think it is a good idea to move this into the kernel driver. I don't
have a slcan device, but a quick peek at its protocol suggests that
it can be done much easier and cleaner than in can327.

Fun fact: The use of a userspace "ignition" tool is a possible use case
baked into can327's design ;)

There is only one use case I can see for it though: Probing the
ELM327's baud rate, and/or setting it before attaching the ldisc. This
is the single thing that the kernel driver cannot do, since it is
attached to an already running TTY, with a fixed speed. Everything else
is configurable via "ip link".

slcand could be used to auto-probe and set the baud rate as well.

Then again, these stripped-down tools could likely be implemented as
shell scripts calling stty and ldattach...

Max