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From:   Dario Binacchi <dario.binacchi@amarulasolutions.com>
Date:   Thu, 9 Jun 2022 10:52:03 +0200
Message-ID: <CABGWkvq2nbfYRww0KWB1YxLQ92hjsWjfV9+nT-cKzc5FPF=DzA@mail.gmail.com>
Subject: Re: [RFC PATCH 11/13] can: slcan: add ethtool support to reset
 adapter errors
To:     Marc Kleine-Budde <mkl@pengutronix.de>
Cc:     linux-kernel@vger.kernel.org,
        Amarula patchwork <linux-amarula@amarulasolutions.com>,
        michael@amarulasolutions.com,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Vincent Mailhol <mailhol.vincent@wanadoo.fr>,
        Wolfgang Grandegger <wg@grandegger.com>,
        linux-can@vger.kernel.org, netdev@vger.kernel.org
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Precedence: bulk

Hi Marc,

On Thu, Jun 9, 2022 at 10:01 AM Marc Kleine-Budde <mkl@pengutronix.de> wrote:
>
> On 09.06.2022 09:24:14, Dario Binacchi wrote:
> > > > > I'm a big fan of bringing the device into a well known good state during
> > > > > ifup. What would be the reasons/use cases to not reset the device?
> > > >
> > > > Because by default either slcand and slcan_attach don't reset the
> > > > error states, but you must use the `-f' option to do so. So, I
> > > > followed this use case.
> > >
> > > Is this a CAN bus error state, like Bus Off or some controller (i.e. non
> > > CAN related) error?
> >
> > The help option of slcan_attach and slcand prints " -f (read status
> > flags with 'F\\r' to reset error states)\n" I looked at the sources of
> > the adapter I am using (USBtin, which uses the mcp2515 controller).
> > The 'F' command reads the EFLG register (0x2d) without resetting the
> > RX0OVR and RX1OVR overrun bits.
>
> The Lawicel doc [1] says 'F' is to read the status flags not to clear
> it. However commit 7ef581fec029 ("slcan_attach: added '-f' commandline
> option to read status flags") [2] suggests that there are some adapters
> that the reading of the status flag clears the errors. IMHO the 'F'
> command should be send unconditionally during open.

When in doubt I would follow the slcand / slcan_attach approach, that don't
send the 'F \ r' command by default. We would be more backward compatible
as regards the sequence of commands to be sent to the controller.

>
> [1] http://www.can232.com/docs/can232_v3.pdf
> [2] https://github.com/linux-can/can-utils/commit/7ef581fec0298a228baa71372ea5667874fb4a56
>
> > The error states reset is done by 'f <subcmd>' command, that is not
> > managed by slcan_attach/slcand.
>
> Is the 'f' command is non-standard?

It's possible.

Thanks and regards,
Dario

>
> >         switch (subcmd) {
> >             case 0x0: // Disable status reporting
> >                 mcp2515_write_register(MCP2515_REG_CANINTE, 0x00);
> >                 return CR;
> >             case 0x1: // Enable status reporting
> >                 mcp2515_write_register(MCP2515_REG_CANINTE, 0x20); //
> > ERRIE interrupt to INT pin
> >                 return CR;
> >             case 0x2: // Clear overrun errors
> >                 mcp2515_write_register(MCP2515_REG_EFLG, 0x00);
> >                 return CR;
> >             case 0x3: // Reinit/reset MCP2515 to clear all errors
> >                 if (state == STATE_CONFIG) {
> >                     mcp2515_init();
> >                     return CR;
> >                 }
> >                 break;
> >         }
>
> 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 |


-- 

Dario Binacchi

Embedded Linux Developer

dario.binacchi@amarulasolutions.com

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