netdev - Re: [RFC PATCH 06/13] can: slcan: allow to send commands to the adapter

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Date:   Sun, 12 Jun 2022 12:39:31 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
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>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [RFC PATCH 06/13] can: slcan: allow to send commands to the
 adapter

On 11.06.2022 23:43:47, Dario Binacchi wrote:
> Hi Marc,
> 
> On Thu, Jun 9, 2022 at 9:16 AM Marc Kleine-Budde <mkl@...gutronix.de> wrote:
> >
> > On 07.06.2022 11:47:45, Dario Binacchi wrote:
> > > This is a preparation patch for the upcoming support to change the
> > > bitrate via ip tool, reset the adapter error states via the ethtool API
> > > and, more generally, send commands to the adapter.
> > >
> > > Since some commands (e. g. setting the bitrate) will be sent before
> > > calling the open_candev(), the netif_running() will return false and so
> > > a new flag bit (i. e. SLF_XCMD) for serial transmission has to be added.
> > >
> > > Signed-off-by: Dario Binacchi <dario.binacchi@...rulasolutions.com>
> >
> > I think this patch can be dropped, let me explain:
> >
> > You don't have to implement the do_set_bittiming callback. It's
> > perfectly OK to set the bitrate during the ndo_open callback after
> > open_candev().
> 
> I developed what you suggested (i. e. remove the SLF_XCMD bit and set the
> bitrate, as well as send the "F\r" and "O\r" commands, after calling
> the open_candev(),

Note:
Max Staudt noticed that you need a do_set_bittiming() callback if you
have only fixed bitrates. I've create a patch that you can have fixed
bit rate only an no do_set_bittiming() callback.

| https://lore.kernel.org/all/20220611144248.3924903-1-mkl@pengutronix.de/

Or use the can-next/master branch as your base.

> but now I can't send the close command ("C\r") during the ndo_stop() since
> netif_running() returns false. The CAN framework clears netif_running() before
> calling the ndo_stop(). IMHO the SLF_XCMD bit then becomes necessary to
> transmit the commands to the adapter from the ndo_open() and
> ndo_stop() routines.
> Any suggestions ?

I see. Keep the setting of the bit rate in the ndo_open(), add the
SLF_XCMD so that you can send messages in ndo_close().

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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