linux-kernel - Re: [RFC PATCH 04/13] can: slcan: use CAN network device driver API

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Date:   Thu, 9 Jun 2022 09:07:49 +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 04/13] can: slcan: use CAN network device driver API

On 08.06.2022 18:42:09, Dario Binacchi wrote:
> > > 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 (-1) before
> > > it is called.
> >
> > What does
> >
> > | ip --details -s -s link show
> >
> > show as the bit rate?
> 
> # ip --details -s -s link show dev can0

This is the bitrate configured with "ip"?

>  can0: <NOARP,UP,LOWER_UP> mtu 16 qdisc pfifo_fast state UP mode
> DEFAULT group default qlen 10
>     link/can  promiscuity 0 minmtu 0 maxmtu 0
>     can state ERROR-ACTIVE restart-ms 0
>   bitrate 500000 sample-point 0.875
>   tq 41 prop-seg 20 phase-seg1 21 phase-seg2 6 sjw 1
>   slcan: tseg1 2..256 tseg2 1..128 sjw 1..128 brp 1..256 brp-inc 1
>   clock 24000000
>   re-started bus-errors arbit-lost error-warn error-pass bus-off
>   0          0          0          0          0          0
> numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535
>     RX: bytes  packets  errors  dropped overrun mcast
>     292        75       0       0       0       0
>     RX errors: length   crc     frame   fifo    missed
>                0        0       0       0       0
>     TX: bytes  packets  errors  dropped carrier collsns
>     0          0        0       0       0       0
>     TX errors: aborted  fifo   window heartbeat transns
>                0        0       0       0       1
> 
> And after applying your suggestions about using the CAN framework
> support for setting the fixed bit rates (you'll
> find it in V2), this is the output instead:

This looks good.

> # ip --details -s -s link show dev can0
> 5: can0: <NOARP,UP,LOWER_UP> mtu 16 qdisc pfifo_fast state UP mode
> DEFAULT group default qlen 10
>     link/can  promiscuity 0 minmtu 0 maxmtu 0
>     can state ERROR-ACTIVE restart-ms 0
>   bitrate 500000
>      [   10000,    20000,    50000,   100000,   125000,   250000,
>         500000,   800000,  1000000 ]
>   clock 0
>   re-started bus-errors arbit-lost error-warn error-pass bus-off
>   0          0          0          0          0          0
> numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535
>     RX: bytes  packets  errors  dropped overrun mcast
>     37307      4789     0       0       0       0
>     RX errors: length   crc     frame   fifo    missed
>                0        0       0       0       0
>     TX: bytes  packets  errors  dropped carrier collsns
>     7276       988      0       0       0       0
>     TX errors: aborted  fifo   window heartbeat transns
>                0        0       0       0       1

Can you configure the bitrate with slcand and show the output of "ip
--details -s -s link show dev can0". I fear it will show 4294967295 as
the bitrate, which I don't like.

A hack would be to replace the -1 by 0 in the CAN netlink code.

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
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