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

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Date:   Thu, 9 Jun 2022 09:24:14 +0200
From:   Dario Binacchi <dario.binacchi@...rulasolutions.com>
To:     Marc Kleine-Budde <mkl@...gutronix.de>
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

Hi Marc,

On Thu, Jun 9, 2022 at 8:38 AM Marc Kleine-Budde <mkl@...gutronix.de> wrote:
>
> On 08.06.2022 18:33:08, Dario Binacchi wrote:
> > Hi Marc,
> >
> > On Tue, Jun 7, 2022 at 12:52 PM Marc Kleine-Budde <mkl@...gutronix.de> wrote:
> > >
> > > On 07.06.2022 11:47:50, Dario Binacchi wrote:
> > > > This patch adds a private flag to the slcan driver to switch the
> > > > "err-rst-on-open" setting on and off.
> > > >
> > > > "err-rst-on-open" on  - Reset error states on opening command
> > > >
> > > > "err-rst-on-open" off - Don't reset error states on opening command
> > > >                         (default)
> > > >
> > > > The setting can only be changed if the interface is down:
> > > >
> > > >     ip link set dev can0 down
> > > >     ethtool --set-priv-flags can0 err-rst-on-open {off|on}
> > > >     ip link set dev can0 up
> > > >
> > > > Signed-off-by: Dario Binacchi <dario.binacchi@...rulasolutions.com>
> > >
> > > 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 error states reset is done by 'f <subcmd>' command, that is not
managed by slcan_attach/slcand.

        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;
        }


Thanks and regards,
Dario

>
> regards,
> 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@...rulasolutions.com

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