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From:   Dario Binacchi <dario.binacchi@amarulasolutions.com>
Date:   Wed, 27 Jul 2022 19:28:45 +0200
Message-ID: <CABGWkvqF4HSKVrO8W8oyDPCMfx_B2xQZ_EWET11RZb6k8Kmb=w@mail.gmail.com>
Subject: Re: [RFC PATCH v3 8/9] can: slcan: add support to set bit time
 register (btr)
To:     Marc Kleine-Budde <mkl@pengutronix.de>
Cc:     linux-kernel@vger.kernel.org, linux-can@vger.kernel.org,
        Oliver Hartkopp <socketcan@hartkopp.net>,
        michael@amarulasolutions.com,
        Amarula patchwork <linux-amarula@amarulasolutions.com>,
        Jeroen Hofstee <jhofstee@victronenergy.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Wolfgang Grandegger <wg@grandegger.com>,
        netdev@vger.kernel.org,
        Vincent Mailhol <mailhol.vincent@wanadoo.fr>,
        Max Staudt <max@enpas.org>
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On Wed, Jul 27, 2022 at 7:21 PM Marc Kleine-Budde <mkl@pengutronix.de> wrote:
>
> On 27.07.2022 17:55:10, Dario Binacchi wrote:
> > Hello Marc,
> >
> > On Wed, Jul 27, 2022 at 1:31 PM Marc Kleine-Budde <mkl@pengutronix.de> wrote:
> > >
> > > On 26.07.2022 23:02:16, Dario Binacchi wrote:
> > > > It allows to set the bit time register with tunable values.
> > > > The setting can only be changed if the interface is down:
> > > >
> > > > ip link set dev can0 down
> > > > ethtool --set-tunable can0 can-btr 0x31c
> > > > ip link set dev can0 up
> > >
> > > As far as I understand, setting the btr is an alternative way to set the
> > > bitrate, right?
> >
> > I thought of a non-standard bitrate or, in addition to the bitrate, the
> > possibility of enabling some specific CAN controller options. Maybe Oliver
> > could help us come up with the right answer.
> >
> > This is the the slcan source code:
> > https://github.com/linux-can/can-utils/blob/cad1cecf1ca19277b5f5db39f8ef6f8ae426191d/slcand.c#L331
> > btr case cames after speed but they don't seem to be considered alternative.
> >
> > > I don't like the idea of poking arbitrary values into a
> > > hardware from user space.
> >
> > However this is already possible through the slcand and slcan_attach
> > applications.
> > Furthermore, the driver implements the LAWICEL ASCII protocol for CAN
> > frame transport over serial lines,
> > and this is one of the supported commands.
> >
> > >
> > > Do you have a use case for this?
> >
> > I use the applications slcand and slcan_attach as a reference, I try to make the
> > driver independent from them for what concerns the CAN setup. And the bit time
> > register setting is the last dependency.
>
> Ok - We avoided writing bit timing registers from user space into the
> hardware for all existing drivers. If there isn't a specific use case,
> let's skip this patch. If someone comes up with a use case we can think
> of a proper solution.

Ok. So do I also remove the 7/9 "ethtool: add support to get/set CAN
bit time register"
patch ?

Thanks and regards,
Dario

>
> Marc
>
> --
> Pengutronix e.K.                 | Marc Kleine-Budde           |
> Embedded Linux                   | https://www.pengutronix.de  |
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> Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |


-- 

Dario Binacchi

Embedded Linux Developer

dario.binacchi@amarulasolutions.com

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