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

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Date:   Tue, 7 Jun 2022 21:19:54 +0900
From:   Vincent MAILHOL <mailhol.vincent@...adoo.fr>
To:     Dario Binacchi <dario.binacchi@...rulasolutions.com>
Cc:     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,
        Max Staudt <max@...as.org>
Subject: Re: [RFC PATCH 00/13] can: slcan: extend supported features

+CC: Max Staudt <max@...as.org>

On Tue. 7 Jun. 2022 at 18:47, Dario Binacchi
<dario.binacchi@...rulasolutions.com> wrote:
> This series originated as a result of CAN communication tests for an
> application using the USBtin adapter (https://www.fischl.de/usbtin/).
> The tests showed some errors but for the driver everything was ok.
> Also, being the first time I used the slcan driver, I was amazed that
> it was not possible to configure the bitrate via the ip tool.
> For these two reasons, I started looking at the driver code and realized
> that it didn't use the CAN network device driver interface.
>
> Starting from these assumptions, I tried to:
> - Use the CAN network device driver interface.
> - Set the bitrate via the ip tool.
> - Send the open/close command to the adapter from the driver.
> - Add ethtool support to reset the adapter errors.
> - Extend the protocol to forward the adapter CAN communication
>   errors and the CAN state changes to the netdev upper layers.
>
> Except for the protocol extension patches (i. e. forward the adapter CAN
> communication errors and the CAN state changes to the netdev upper
> layers), the whole series has been tested. Testing the extension
> protocol patches requires updating the adapter firmware. Before modifying
> the firmware I think it makes sense to know if these extensions can be
> considered useful.
>
> Before applying the series I used these commands:
>
> slcan_attach -f -s6 -o /dev/ttyACM0
> slcand ttyACM0 can0
> ip link set can0 up
>
> After applying the series I am using these commands:
>
> slcan_attach /dev/ttyACM0
> slcand ttyACM0 can0
> ip link set dev can0 down
> ip link set can0 type can bitrate 500000
> ethtool --set-priv-flags can0 err-rst-on-open on
> ip link set dev can0 up

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?

> Now there is a clearer separation between serial line and CAN,
> but above all, it is possible to use the ip and ethtool commands
> as it happens for any CAN device driver. The changes are backward
> compatible, you can continue to use the slcand and slcan_attach
> command options.

Yours sincerely,
Vincent Mailhol