netdev - Re: [PATCH v4 05/12] can: slcan: use CAN network device driver API

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Message-ID: <20220628092833.uo66jbnwhh5af6je@pengutronix.de>
Date:   Tue, 28 Jun 2022 11:28:33 +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>,
        Oliver Hartkopp <socketcan@...tkopp.net>,
        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: [PATCH v4 05/12] can: slcan: use CAN network device driver API

On 14.06.2022 14:28:14, Dario Binacchi wrote:
> As suggested by commit [1], now the driver uses the functions and the
> data structures provided by the CAN network device driver interface.
> 
> Currently the driver doesn't implement a way to set bitrate for SLCAN
> based devices via ip tool, so you'll have to do this by slcand or
> slcan_attach invocation through the -sX parameter:
> 
> - slcan_attach -f -s6 -o /dev/ttyACM0
> - slcand -f -s8 -o /dev/ttyUSB0
> 
> where -s6 in will set adapter's bitrate to 500 Kbit/s and -s8 to
> 1Mbit/s.
> See the table below for further CAN bitrates:
> - s0 ->   10 Kbit/s
> - s1 ->   20 Kbit/s
> - s2 ->   50 Kbit/s
> - s3 ->  100 Kbit/s
> - s4 ->  125 Kbit/s
> - s5 ->  250 Kbit/s
> - s6 ->  500 Kbit/s
> - s7 ->  800 Kbit/s
> - s8 -> 1000 Kbit/s
> 
> In doing so, the struct can_priv::bittiming.bitrate of the driver is not
> set and since the open_candev() checks that the bitrate has been set, it
> must be a non-zero value, the bitrate is set to a fake value (-1U)
> before it is called.
> 
> The patch also changes the slcan_devs locking from rtnl to spin_lock. The
> change was tested with a kernel with the CONFIG_PROVE_LOCKING option
> enabled that did not show any errors.

You're not allowed to call alloc_candev() with a spin_lock held. See
today's kernel test robot mail:

| https://lore.kernel.org/all/YrpqO5jepAvv4zkf@xsang-OptiPlex-9020

I think it's best to keep the rtnl for now.

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 |

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