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

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Message-ID: <CABGWkvotv4Ebm7OSbp=oQ7vwHhR_=sXfAAEkngjLm2faYrUFPw@mail.gmail.com>
Date:   Wed, 8 Jun 2022 18:42:09 +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>,
        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

Hi Marc,

On Tue, Jun 7, 2022 at 1:13 PM Marc Kleine-Budde <mkl@...gutronix.de> wrote:
>
> On 07.06.2022 11:47:43, 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.
> >
> > There is no way to set bitrate for SLCAN based devices via ip tool, so
>   ^^^^^^^^^^^^^^^
> Currently the driver doesn't implement a way

Ok, I'll do it.

>
> > you'll have to do this by slcand/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 (-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
 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:

# 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

Thanks and regards,
Dario

>
> 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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