linux-kernel - Re: [PATCH 1/2] can: dummy_can: add CAN termination support

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Message-ID: <20260112174356.10358-1-rakuram.e96@gmail.com>
Date: Mon, 12 Jan 2026 23:13:55 +0530
From: Rakuram Eswaran <rakuram.e96@...il.com>
To: mailhol@...nel.org
Cc: corbet@....net,
	davem@...emloft.net,
	edumazet@...gle.com,
	horms@...nel.org,
	kuba@...nel.org,
	linux-can@...r.kernel.org,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	mkl@...gutronix.de,
	netdev@...r.kernel.org,
	pabeni@...hat.com,
	rakuram.e96@...il.com,
	socketcan@...tkopp.net
Subject: Re: [PATCH 1/2] can: dummy_can: add CAN termination support

On Thu, 1 Jan 2026 at 17:42, Vincent Mailhol <mailhol@...nel.org> wrote:
>
> On 31/12/2025 at 19:13, Rakuram Eswaran wrote:
> > Add support for configuring bus termination in the dummy_can driver.
> > This allows users to emulate a properly terminated CAN bus when
> > setting up virtual test environments.
> >
> > Signed-off-by: Rakuram Eswaran <rakuram.e96@...il.com>
> > ---
> > Tested the termination setting using below iproute commands:
> >
> >   ip link set can0 type can termination 120
> >   ip link set can0 type can termination off
> >   ip link set can0 type can termination potato
> >   ip link set can0 type can termination 10000
> >  
> >  drivers/net/can/dummy_can.c | 25 +++++++++++++++++++++++--
> >  1 file changed, 23 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/can/dummy_can.c b/drivers/net/can/dummy_can.c
> > index 41953655e3d3c9187d6574710e6aa90fc01c92a7..418d9e25bfca1c7af924ad451c8dd8ae1bca78a3 100644
> > --- a/drivers/net/can/dummy_can.c
> > +++ b/drivers/net/can/dummy_can.c
> > @@ -86,6 +86,11 @@ static const struct can_pwm_const dummy_can_pwm_const = {
> >       .pwmo_max = 16,
> >  };
> >
> > +static const u16 dummy_can_termination_const[] = {
> > +     CAN_TERMINATION_DISABLED,       /* 0 = off */
> > +     120,                            /* 120 Ohms */
>
> Nitpick: no need to explain that disabled means "off", the first comment
> can be removed. Also, to be consistent with how the can.bitrate_max and
> can.clock.freq are declared, you can add the unit just next to the value.
>
>         static const u16 dummy_can_termination_const[] = {
>                 CAN_TERMINATION_DISABLED,
>                 120 /* Ohms */,
>         };
>
> (above comment is notwithstanding).
>

Yes, this looks better. 

> > +};
> > +
> >  static void dummy_can_print_bittiming(struct net_device *dev,
> >                                     struct can_bittiming *bt)
> >  {
> > @@ -179,6 +184,16 @@ static void dummy_can_print_bittiming_info(struct net_device *dev)
> >       netdev_dbg(dev, "\n");
> >  }
> >
> > +static int dummy_can_set_termination(struct net_device *dev, u16 term)
> > +{
> > +     struct dummy_can *priv = netdev_priv(dev);
> > +
> > +     netdev_dbg(dev, "set termination to %u Ohms\n", term);
> > +     priv->can.termination = term;
> > +
> > +     return 0;
> > +}
> > +
> >  static int dummy_can_netdev_open(struct net_device *dev)
> >  {
> >       int ret;
> > @@ -243,17 +258,23 @@ static int __init dummy_can_init(void)
> >       dev->ethtool_ops = &dummy_can_ethtool_ops;
> >       priv = netdev_priv(dev);
> >       priv->can.bittiming_const = &dummy_can_bittiming_const;
> > -     priv->can.bitrate_max = 20 * MEGA /* BPS */;
> > -     priv->can.clock.freq = 160 * MEGA /* Hz */;
>
> Don't add unrelated changes to your patch. Your patch should do one
> thing (here: add the resistance termination). If you want to reorder the
> existing lines, that should go in a separate clean-up patch. But here,
> there is no need to touch those lines, so just drop this reorder.
>

Ack. I will revert these unrelated changes.

> >       priv->can.fd.data_bittiming_const = &dummy_can_fd_databittiming_const;
> >       priv->can.fd.tdc_const = &dummy_can_fd_tdc_const;
> >       priv->can.xl.data_bittiming_const = &dummy_can_xl_databittiming_const;
> >       priv->can.xl.tdc_const = &dummy_can_xl_tdc_const;
> >       priv->can.xl.pwm_const = &dummy_can_pwm_const;
> > +     priv->can.bitrate_max = 20 * MEGA /* BPS */;
> > +     priv->can.clock.freq = 160 * MEGA /* Hz */;
> > +     priv->can.termination_const_cnt = ARRAY_SIZE(dummy_can_termination_const);
> > +     priv->can.termination_const = dummy_can_termination_const;
> > +
> >       priv->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY |
> >               CAN_CTRLMODE_FD | CAN_CTRLMODE_TDC_AUTO |
> >               CAN_CTRLMODE_RESTRICTED | CAN_CTRLMODE_XL |
> >               CAN_CTRLMODE_XL_TDC_AUTO | CAN_CTRLMODE_XL_TMS;
> > +
> > +     priv->can.do_set_termination = dummy_can_set_termination;
> > +
> >       priv->dev = dev;
> >
> >       ret = register_candev(priv->dev);
>
> Aside from the above remark this is OK. Please send a v2 with that last
> remark addressed. You can also add my review tag:
>
> Reviewed-by: Vincent Mailhol <mailhol@...nel.org>
>

Thanks, Vincent. I will make the change as mentioned above and send v2.

Best Regards,
Rakuram