netdev - Re: [RFC PATCH 11/13] can: slcan: add ethtool support to reset adapter errors

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Message-ID: <20220609080112.24bw2764ov767pqc@pengutronix.de>
Date:   Thu, 9 Jun 2022 10:01:12 +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>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Vincent Mailhol <mailhol.vincent@...adoo.fr>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        linux-can@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [RFC PATCH 11/13] can: slcan: add ethtool support to reset
 adapter errors

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.

[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?

>         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  |
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